AGM batteries damaging Motorhome chargers

[aandncaravan]

Just in case anyone thought it had stopped happening, chargers are still regularly being damaged by AGM batteries once the AGM batteries get past about 18 months old.

Had 6 this month, and reports of two today, this request has just come in and is typical :

 

"Hymer Exsis i504 2015, Schaudt Elektroblock EBL29, Varta AGM LA95 12v 95Ah Battery.

Leisure battery not charging on EHU charger but fine from alternator. Display panel not showing EHU symbol but Mains power sockets working OK.

Live in mid Wales and can visit at short notice.

Call back would be appreciated".

 

 

The AGM battery page has been heavily revised recently with additional supporting evidence as to why we think they are unsuited to Motorhome use : .http://www.aandncaravanservices.co.uk/agm-batteries.php

 

 

[Gerry McG]

Just clarifying...

Are your observations re. AGM batteries and MH use principally related to MH with older EBL that don't have a specific AGM charging profile?

e.g. Our new MH has a Schaudt EBL 119, with a specific AGM charging profile, so am I correct in thinking that the issues you describe are of less relevance in this situation?

[aandncaravan]

The EBL 119 helps, but not yet seen a Motorhome with a 14.8v Alternator, and these days that seems to be a more primary charge method.

 

The charging is only part of the story. Motorhome 12v 'Power consumption' has changed dramatically in the last 5 years. Far more 12v is used, and in big chunks of current, than ever before. That is usage that AGM batteries do not take to. Especially so if done in a warm clime, like sunny Spain and more people than ever are heading South.

 

 

A perfect example today of how AGM batteries are being mis-sold :

 

I got a call mid morning : "Help the Caravan is stuck on the road, I can't get it up the drive because the MotorMover has failed".

 

I am supposed to be resting prior to my Operation next Tuesday but he was local and it didn't sound like it was going to be hard work, so I went out.

 

It was easy to sort because the battery was absolutely destroyed. An AGM battery just 7 months old. So I just fitted a replacement supplied by the customer which he sourced down the road.

 

Now bear with because this is very relevant to AGM's in a Motorhome.

 

Because of the way the Caravan is used, an AGM could not have been a worse choice, as it is for most Motor Mover equipped Caravans.

 

The owner gave me a perfect demonstration of just why :

 

This gentleman is not physically able to manhandle his caravan even on the flat, and won't/can't use the car to reverse with it on the Tow hitch. The storage space next to the house is up a long sloping drive, the start of which is quite a sharp turn. He didn't want me to go until he got it parked up.

 

To manoeuvre the Caravan from the road up the drive and into position took about 15 - 20 minutes.

 

The battery terminals of the replacement Varta LFD 90 were very warm to the touch by the time the Caravan was in place. The casing was cooler but still warmer than ambient, about 35 degrees?

 

The owner remarked how 'fantastic' the new battery was, "normally it slows right down before I get halfway to the top of the slope. This new battery kept it moving more sprightly and right to the top. Never had that with any other battery. I believe you now, it is different!!".

 

The Varta LFD90 is tolerant of even dessert temperatures but is clearly going to struggle if used like this. However a Gel or AGM is going to be roasted because the Acid is in such an immobile form, either a thick Gel or absorbed in Glass Fibre Matt.

 

In a Wet Acid battery like a Varta LFD90 the acid is liquid and very mobile. As it warms it rises by convection not only carrying the heat away from the Plates but brings cooler, and crucially, fresh acid from below.

 

Clearly a Gel or absorbed matt acid is going to transfer heat more slowly. But, just as significantly, fresh acid is not going to be able to quickly replace the acid at the Plate surface which is being exhausted by the chemical reaction.

As a result, the chemical reaction will slow with power production reducing, exactly as was witnessed on the original AGM battery with the Caravan 'slowing down' the further it got up the slope.

 

That suggests that the acid at the plates had become 'exhausted' in the AGM half way into the vans journey, by which time the temperature at the plates must have also been high. If prolonged chemical reaction that resulted in drop off, must have also generated a lot of heat as a by product?

 

The AGM's Plate temperature by the time it reached the top of the slope must have been damagingly high.

 

 

The owner wouldn't give permission to cut open the old AGM battery as he wanted it to go back to the supplier for a refund on the grounds it was not fit for purpose.

The supplier had specifically directed him towards this particular 'twice the cost' battery as being the most suitable for a Motor Mover equipped Caravan.

 

I argued that if we cut the battery open the retailer would not be able to argue with the damage that I was pretty sure we would see inside.

I was desperate to see inside this one, but I understood his stance, so didn't argue

 

This battery was so young the only damage inside would have to be pure Heat degradation which would have been nice to have compared to those AGM's we have opened after what we think was 'charging degradation'.

 

 

An AGM battery can tolerate high current discharges for a few seconds without any harm, because little heat will be generated as the power will come from the 'Plates Surface', not so much by chemical reaction.

 

But any use that raises the Plate temperature, like the 150amps from a 1,600watt Inverter for even minutes, will massively shorten the batteries life.

 

This is especially so if the ambient temperature is higher than 30degrees, as any significant use at these sort of temperatures will cause harm, either charging or discharging.

 

One very clued up battery manufacturer states for it's AGM's:

 

"The charge current should preferably not exceed 20 A for a 100 Ah battery, otherwise the temperature of a battery will increase by more than 10°C"

 

They then go on to present a chart that shows how temperature affects an AGM/Gels life.

Their chart below shows how an AGM battery drops from a 7 - 10 year life, right down to a paltry 2 years AT JUST 40 DEGREES Float Service!! And these are ultra expensive high quality AGM batteries.

See chart below.

 

The Yuasa website states that a constant, continuous charge, just like a constant continuous current draw, is not suitable for some batteries. The ONLY battery technology they highlight to being 'weak' in this situation as AGM technology. They write :

 

"1. CONSTANT CURRENT CHARGERS -

These maintain a fixed, constant, preset current throughout the charging period irrespective of the battery on-charge voltage. Do NOT charge AGM batteries on a constant current charger."

 

So taking out or putting in continuous current on an AGM, not necessarily a high current either, is an issue according to Yuasa. An issue that is not relevant to any other battery technology.

 

We think this all helps explain why an AGM lasts such a short time in a Motorhome, like in the very first post above.

This isn't just about the charging voltage, however we think that has a big impact in 50% of most degraded Motorhome batteries.

 

 

If your holidays take place in the Artic Circle, you may find an AGM does the trick for you.

But if you like to holiday in Spain in 30 degrees, then you can see from the chart, your AGM/Gel will already be off to a poor start.

 

AGM batteries are being promoted as better for Deep Discharge situations, which can be the case, but ONLY if both the Current in and out, plus temperatures are low.

 

When the average Power draw in a Motorhome is rising, Gel and AGM batteries, just can't compete with the best Wet batteries which operate well in even Dessert temperature conditions.

 

There is more supporting evidence to 'our theory' on the website AGM page : http://www.aandncaravanservices.co.uk/agm-batteries.php

 

 

 

 

[colin]

So can I assume that because my appliances are all low powered this is why my AGM battery of 6 years old is still soldiering on, whilst my wet cab battery is knackered?

[aandncaravan]

Thank you Colin, more supporting evidence?

AGM batteries cost close on £200 a time and are promoted as ultra heavy duty long life batteries, so one should expect close on 8 year life. But there are only a handful that we know of that have made it past 3 years.

 

 

Maybe your Cab battery has expired because it is sharing the 14.8v charge with the AGM?

 

Probably not in reality, but it is an issue we have come across before that when you set the mains charger for one technology, both batteries are treated the same.

 

 

Far better to have the same wet battery technology as Starter and Habitation and set the charger to 'Wet', which is what the EBL 119 was designed for, but 'rush' modified at a later date to cater for AGM.

 

 

 

To answer the question about the EBL 119 in a different way - we have repaired more AGM optimised chargers, like the EBL 30 and EBL 119, this year than ever before. Maybe that answers your question more directly?

 

 

 

[kevina]

NEW AGM BATTERY FROM VICTRON

 

A new AGM battery: the AGM Super Cycle battery A truly innovative battery The AGM Super Cycle batteries are the result of recent battery electrochemistry developments. The paste of the positive plates is less sensitive to softening, even in case of repeated 100% discharge of the battery, and new additives to the electrolyte reduce sulfation in case of deep discharge. Exceptional 100% depth of discharge (DoD) performance Tests have shown that the Super Cycle battery does withstand at least three hundred 100% DoD cycles. The tests consist of a daily discharge to 10,8V with I = 0,2C20, followed by approximately two hours rest in discharged condition, and then a recharge with I = 0,2C20. The two hours rest period in discharged condition will damage most batteries within 100 cycles, but not the Super Cycle battery. We recommend the Super Cycle battery for applications where an occasional discharge to 100% DoD, or frequent discharge to 60-80% DoD is expected. Smaller and lighter An additional advantage of the new chemistry is a slightly smaller size and less weight compared to our standard deep cycle AGM batteries. Low internal resistance The internal resistance is also slightly lower compared to our standard deep cycle AGM batteries.

[aandncaravan]

kevina - 2017-07-15 2:39 PM

 

NEW AGM BATTERY FROM VICTRON

 

A new AGM battery: the AGM Super Cycle battery A truly innovative battery The AGM Super Cycle batteries are the result of recent battery electrochemistry developments. The paste of the positive plates is less sensitive to softening, even in case of repeated 100% discharge of the battery, and new additives to the electrolyte reduce sulfation in case of deep discharge. Exceptional 100% depth of discharge (DoD) performance Tests have shown that the Super Cycle battery does withstand at least three hundred 100% DoD cycles. The tests consist of a daily discharge to 10,8V with I = 0,2C20, followed by approximately two hours rest in discharged condition, and then a recharge with I = 0,2C20. The two hours rest period in discharged condition will damage most batteries within 100 cycles, but not the Super Cycle battery. We recommend the Super Cycle battery for applications where an occasional discharge to 100% DoD, or frequent discharge to 60-80% DoD is expected. Smaller and lighter An additional advantage of the new chemistry is a slightly smaller size and less weight compared to our standard deep cycle AGM batteries. Low internal resistance The internal resistance is also slightly lower compared to our standard deep cycle AGM batteries.

 

 

We repeatedly say on the webpages that Victron Energy are one of the most clued up manufacturers in the World because they design and manufacture battery Chargers as well as batteries resulting in some of the best chargers and batteries in the World.

Hence us using their charts and their figures to show how the immobile acid absorbed in glass fibre will suffer from Heat build up of the Plates.

 

 

You will note that this 'Super' battery still talks about low 20a per100Ah battery(C20) recharge currents, which also means low discharge currents for optimum life.

 

You will also see above that we don't dispute the ability of an AGM to deep discharge better than a wet battery. So long as that discharge and recharge is done at low currents to prevent heat build up.

 

The very nature of an AGM's construction, deliberately making the Acid 'immobile', means it will suffer from heat build up and battery destruction, unless efforts are made to limit that current AND temperature.

 

Just changing the composition of the Paste won't alter that.

Well it might have done IF the description talked of how the new Paste was resistant to Heat degradation from high charge/discharge currents and excelled at high temperatures. But it doesn't.

 

The same limitations that cause issues during Motorhome use are still an inherent part of the design.

 

 

We would not dispute this is a great battery, but the average modern Motorhome, will see the battery deteriorate from heat degradation (and additionally inappropriate charging) way before that cyclic capability is used up.

 

 

And that is using Victron Energy's own charts and figures.

 

 

100% Deep cycle batteries are great, but this is one mega expensive battery.

I would suggest two Varta LFD90's at half the cost and discharged to 50% would not be far off the same performance in the real World in real Motorhome usage?

 

 

[colin]

aandncaravan - 2017-07-15 3:51 PM

 

 

We would not dispute this is a great battery, but the average modern Motorhome, will see the battery deteriorate from heat degradation (and additionally inappropriate charging) way before that cyclic capability is used up.

 

[/qUOTE]

 

It would be much better if a figure was put on charging/discharging currents instead of a blanket 'average modern motorhome'.

You talk of 20amp for a 100ah battery, as a charging limit, our van has a 90ah battery and a ebl99 which I believe has a 16amp charger on mains (which we very rarely use) so roughly the same proportion, I'm not sure if the ebl limits alternator to 16amp? although much of our charging comes from the solar panel which would be doing well to get to 5amp. our max discharging would have been back when we had an old Viewsonic and converted sky box probably 10amp, nowadays I don't think we can even hit 5amp.

I'm guessing people using invertors for microwaves, hairdryiers will be well caning the batteries, and then b2b for charging will also mess them up?

[aandncaravan]

colin - 2017-07-15 5:15 PM

 

aandncaravan - 2017-07-15 3:51 PM

 

 

We would not dispute this is a great battery, but the average modern Motorhome, will see the battery deteriorate from heat degradation (and additionally inappropriate charging) way before that cyclic capability is used up.

 

[/qUOTE]

 

It would be much better if a figure was put on charging/discharging currents instead of a blanket 'average modern motorhome'.

You talk of 20amp for a 100ah battery, as a charging limit, our van has a 90ah battery and a ebl99 which I believe has a 16amp charger on mains (which we very rarely use) so roughly the same proportion, I'm not sure if the ebl limits alternator to 16amp? although much of our charging comes from the solar panel which would be doing well to get to 5amp. our max discharging would have been back when we had an old Viewsonic and converted sky box probably 10amp, nowadays I don't think we can even hit 5amp.

I'm guessing people using invertors for microwaves, hairdryiers will be well caning the batteries, and then b2b for charging will also mess them up?

 

 

Colin, The EBL range do not limit the Alternator current, the current passing will be down to the Alternator and the Battery.

 

 

I would love to be exact in suggesting a discharge/charge figure that might be safe, or otherwise, but ambient temperature plays a big part.

 

Yuasa don't even say the charge current has to be high, They just say it mustn't be constant, for there to be an issue with AGM, and only AGM batteries.

 

According to the Victron charts, just drawing 5 amps, or charging at 4 amps, in 40 degree temperatures might have a life shortening effect on an AGM battery.

 

The technology and manufacturer of the battery will also have an impact.

Some of the budget AGM batteries hitting the market now, probably won't have even 25% of a Victron Energy batteries life.

 

There are so many variables, it isn't possible to talk figures.

All I can do is present 'my theory', the evidence from Victron Energy, Yuasa and broken Battery Chargers to flag there is an issue with AGM batteries.

 

 

One very key difference between AGM battery use in Cars, Helicopters, etc and Motorhomes is that ONLY Motrohomes discharge an AGM battery to 50% or below then drive 500 miles down to the South of France charging them up on the Alternator for hour after hour.

 

Or connecting to EHU for hours after running them down, etc.

 

That happens over and over when some evidence suggests it shouldn't?

That is irrespective of any loads we suggest might be placed on them by Inverters, etc.

 

[aandncaravan]

The owner of the Hymer Exsis that started this post, originally questioned our guess that the battery will have died therefore be the cause of the failure. But has emailed this morning saying,

 

"Never nice to hear that an expensive EBL has been busted by what I took to be an quality battery that is not old!! I checked the battery again and without anything drawing power it has fallen from fully charged to 12.2v in 2 weeks whereas previously it always held charge between trips".

 

So to come back to the original post, regardless of the reason, this owners AGM, like so many others, has died prematurely and knocked out the charger.

 

 

We therefore suggest that if anyone has AGM's fitted, you consider replacement of the habitation battery before 2 years are up.

 

 

[lennyhb]

If you want confirmation of what Alan says just search the German Motorhome forums. Although Hymer group changed from the crap Banner batteries they were fitting to Varta AGM's and the Elektroblocks were updated with an AGM charge cycle, the AGM's are still failing. I didn't want AGM's in my new Hymer after my experience with them in the last Hymer, I fitted 3 x Gel's and they are performing brilliantly.

[david lloyd]

lennyhb - 2017-07-17 11:28 AM

 

If you want confirmation of what Alan says just search the German Motorhome forums. Although Hymer group changed from the crap Banner batteries they were fitting to Varta AGM's and the Elektroblocks were updated with an AGM charge cycle, the AGM's are still failing. I didn't want AGM's in my new Hymer after my experience with them in the last Hymer, I fitted 3 x Gel's and they are performing brilliantly.

 

That's a little worrying Lenny, I eventually managed to sort out the solar charging arrangements on our 2015 Hymer B544 by removing the Visionplus regulator and replacing it with a proper one - the Votronic 165 - and wired it through the EBL29 instead of it being wired direct to the leisure battery with a battery master attached. I also fitted the optional temperature probe. I had thought the arrangement was working much better but I am concerned that the Electroblock has only two positions - wet lead acid or gel/AGM - and that the latter aren't really the same. The Hymer has two Varta AGM95's fitted and, given everything that has been written so far on this and other threads I would certainly replace them with Varta LFD90's or perhaps gel when they are no longer serviceable- but I wouldn't want them to have ruined the EBL before that happens.

 

From Myers crossed.

 

David

[Robbo]

Thanks Allan for initiating this thread - very interesting.

 

This is probably a hypothetical question BUT if I didn't have solar, didn't use EHU (when touring) and just relied on my battery bank - would the alternator be able to provide the correct charging regime to keep my AGM batteries topped up to a reasonable level.

 

As I understand it, the standard alternator is regulated to provide an output of 14.4v or thereabouts. This keeps wet acid/gel batteries happy.

 

When using AGM batteries, does the alternator have to be designed specifically for the higher voltages expected by AGM batteries or do they just adjust the alternator regulator settings.

 

AND if the alternator is AGM specific, does this mimic the AGM charging regime from a 230v mains charger.

 

From "tad confused.com" :-D

[lennyhb]

Robbo - 2017-07-17 4:12 PM

 

Thanks Allan for initiating this thread - very interesting.

 

This is probably a hypothetical question BUT if I didn't have solar, didn't use EHU (when touring) and just relied on my battery bank - would the alternator be able to provide the correct charging regime to keep my AGM batteries topped up to a reasonable level.

 

As I understand it, the standard alternator is regulated to provide an output of 14.4v or thereabouts. This keeps wet acid/gel batteries happy.

 

When using AGM batteries, does the alternator have to be designed specifically for the higher voltages expected by AGM batteries or do they just adjust the alternator regulator settings.

 

AND if the alternator is AGM specific, does this mimic the AGM charging regime from a 230v mains charger.

 

From "tad confused.com" :-D

Some of the latest alternators have the higher output voltage for AGM as most Stop/Start cars use AGM batteries. They don't mimic a proper charging curve as the use is of a starter battery is considerably different to a leisure battery and it's not really necessary in a car environment.

[lennyhb]

david lloyd - 2017-07-17 3:04 PM

 

lennyhb - 2017-07-17 11:28 AM

 

If you want confirmation of what Alan says just search the German Motorhome forums. Although Hymer group changed from the crap Banner batteries they were fitting to Varta AGM's and the Elektroblocks were updated with an AGM charge cycle, the AGM's are still failing. I didn't want AGM's in my new Hymer after my experience with them in the last Hymer, I fitted 3 x Gel's and they are performing brilliantly.

 

That's a little worrying Lenny, I eventually managed to sort out the solar charging arrangements on our 2015 Hymer B544 by removing the Visionplus regulator and replacing it with a proper one - the Votronic 165 - and wired it through the EBL29 instead of it being wired direct to the leisure battery with a battery master attached. I also fitted the optional temperature probe. I had thought the arrangement was working much better but I am concerned that the Electroblock has only two positions - wet lead acid or gel/AGM - and that the latter aren't really the same. The Hymer has two Varta AGM95's fitted and, given everything that has been written so far on this and other threads I would certainly replace them with Varta LFD90's or perhaps gel when they are no longer serviceable- but I wouldn't want them to have ruined the EBL before that happens.

 

From Myers crossed.

 

David

It depends on how the batteries fail if it's bad enough to overload the EBL then you have got problems. If like me you rarely use EHU you will be well aware of them failing long before then.

The most worrying problem is you probably won't get them changed under warranty. The batteries they fit are dual purpose so when they fail and are not good enough for leisure use the will only accept a CCA test that is a cranking test for starter batteries.

When my Banners failed after 18 months on my 2014 Hymer both batteries were only giving 10a/h before the EBL shut down due to low volts, they CCA test they passed at 79% so they wouldn't change them.

On the new van (2017 Hymer) as we were trading and my 2 Gel's were only just over a year old I got the dealer swap my Gels over to the new van and I then fitted a 3rd Gel.

[kevina]

Robbo - 2017-07-17 4:12 PM

 

Thanks Allan for initiating this thread - very interesting.

 

This is probably a hypothetical question BUT if I didn't have solar, didn't use EHU (when touring) and just relied on my battery bank - would the alternator be able to provide the correct charging regime to keep my AGM batteries topped up to a reasonable level.

 

As I understand it, the standard alternator is regulated to provide an output of 14.4v or thereabouts. This keeps wet acid/gel batteries happy.

 

When using AGM batteries, does the alternator have to be designed specifically for the higher voltages expected by AGM batteries or do they just adjust the alternator regulator settings.

 

AND if the alternator is AGM specific, does this mimic the AGM charging regime from a 230v mains charger.

 

From "tad confused.com" :-D

 

Your best bet would be to fit a, properly installed, battery to battery charger. Your batteries would then get a controlled AGM specific charge.

[aandncaravan]

Robbo - 2017-07-17 4:12 PM

 

Thanks Allan for initiating this thread - very interesting.

 

This is probably a hypothetical question BUT if I didn't have solar, didn't use EHU (when touring) and just relied on my battery bank - would the alternator be able to provide the correct charging regime to keep my AGM batteries topped up to a reasonable level.

 

As I understand it, the standard alternator is regulated to provide an output of 14.4v or thereabouts. This keeps wet acid/gel batteries happy.

 

When using AGM batteries, does the alternator have to be designed specifically for the higher voltages expected by AGM batteries or do they just adjust the alternator regulator settings.

 

AND if the alternator is AGM specific, does this mimic the AGM charging regime from a 230v mains charger.

 

From "tad confused.com" :-D

 

 

It is the regulator that determines the output voltage in a conventional Alternator. So in theory you could fit a 14.8v regulator to a '14'4v' Alternator. Obviously someone doing this needs to make sure the Starter Battery is 14.8v capable.

 

 

However most Cars fitted with AGM batteries employ an ECU controlled Alternator

Where the ECU not only decides the Alternator charging voltage, which can be anything from 13.2v to 15v, but also the charging current rate.

When an AGM battery needs charging it will get full current and 14.8v, if the battery is full, the current drops and so does the voltage, typically to 13.2v - 13.6v, all controlled by the ECU.

So yes an AGM 'specific' Alternator generally mimics a 230v mains charger, as AGM's don't like a high 14.4v float/trickle voltage.

 

 

Ford were one of the biggest early adopters of the ECU controlled Alternator, I think around 2005 and pre Stop/Start. It was fitted on the Focus, Mondeo and Transit and maybe others.

 

This early system would charge the Starter battery, a Special Silver technology battery, at 15+ volts when the battery was cold, dropping to a normal 14.4v once the battery warmed up.

Once the battery was fully charged the Alternator dropped to under 14v to save fuel.

 

While we have seen the system active on Transit vans, never seen it active on a Transit Motorhome, so I assume the factory 'deactivate' the feature within the ECU when a Chassis is designated for 'Conversion'?

 

The special Silver technology batteries, not dissimilar to the Varta Powerframe LFD90, have recorded long lives in this application. However, 'after market' Calcium based batteries are notorious for having very short lives if used on these Alternators.

 

 

But the limitations of an AGM is not just about how fussy they are on the current going in, but prone to degradation when you take it out.

It is only in the last 12 months or so that we have begun to see indications that current and, continuous draw of it, is as big an issue as charging.

 

 

 

 

 

 

[Brian Kirby]

A question. Does this rate of AGM failure point to the general unsuitability of this battery technology for leisure use in motorhomes, or only when the pattern of use involves relatively rapid, deep, discharge (likely to be the case for those who live off grid), with subsequent re-charging (I suspect often to less than a full charge) via a relatively unsophisticated vehicle alternator charge regime?

 

I ask for two reasons:

 

1) because those who use their vans in this way seem to find gel or flooded batteries tolerate their use pattern.

 

2) because those who habitually use EHU, so generally limiting the depth of discharge of the battery, but also generally fully re-charging it via the more sophisticated (even of not AGM specific) regime of the on-board charger, seem not to encounter the same failure rates.

 

It seems we may simply be saying that if you work your battery hard, with repeated, heavy, fairly rapid discharges, and with (at times partial) re-charging via the alternator, you should consider substituting gel or flooded for AGM sooner rather than later, whereas those who give their battery an easy time, generally maintaining it at near full charge via a sophisticated mains charger, have little to worry about.

 

I just wonder if we may be creating a bit of an unnecessary anti-AGM panic, whereas it is the mis-match between AGM technology and certain patterns of use, that we should be our focus. I'm not arguing that AGM batteries are "right" for general supply as motorhome leisure batteries. Clearly they are not, as the seller doesn't know (or ask) how the buyer will use their van, and then supply an appropriate battery. I'm just a bit concerned that some folk may be persuaded to replace their relatively expensive AGM battery with an alternative technology, when they had no real need to do so.

[Robbo]

aandncaravan - 2017-07-17 9:04 PM

 

Robbo - 2017-07-17 4:12 PM

 

Thanks Allan for initiating this thread - very interesting.

 

This is probably a hypothetical question BUT if I didn't have solar, didn't use EHU (when touring) and just relied on my battery bank - would the alternator be able to provide the correct charging regime to keep my AGM batteries topped up to a reasonable level.

 

As I understand it, the standard alternator is regulated to provide an output of 14.4v or thereabouts. This keeps wet acid/gel batteries happy.

 

When using AGM batteries, does the alternator have to be designed specifically for the higher voltages expected by AGM batteries or do they just adjust the alternator regulator settings.

 

AND if the alternator is AGM specific, does this mimic the AGM charging regime from a 230v mains charger.

 

From "tad confused.com" :-D

 

 

It is the regulator that determines the output voltage in a conventional Alternator. So in theory you could fit a 14.8v regulator to a '14'4v' Alternator. Obviously someone doing this needs to make sure the Starter Battery is 14.8v capable.

 

 

However most Cars fitted with AGM batteries employ an ECU controlled Alternator

Where the ECU not only decides the Alternator charging voltage, which can be anything from 13.2v to 15v, but also the charging current rate.

When an AGM battery needs charging it will get full current and 14.8v, if the battery is full, the current drops and so does the voltage, typically to 13.2v - 13.6v, all controlled by the ECU.

So yes an AGM 'specific' Alternator generally mimics a 230v mains charger, as AGM's don't like a high 14.4v float/trickle voltage.

 

 

Ford were one of the biggest early adopters of the ECU controlled Alternator, I think around 2005 and pre Stop/Start. It was fitted on the Focus, Mondeo and Transit and maybe others.

 

This early system would charge the Starter battery, a Special Silver technology battery, at 15+ volts when the battery was cold, dropping to a normal 14.4v once the battery warmed up.

Once the battery was fully charged the Alternator dropped to under 14v to save fuel.

 

While we have seen the system active on Transit vans, never seen it active on a Transit Motorhome, so I assume the factory 'deactivate' the feature within the ECU when a Chassis is designated for 'Conversion'?

 

The special Silver technology batteries, not dissimilar to the Varta Powerframe LFD90, have recorded long lives in this application. However, 'after market' Calcium based batteries are notorious for having very short lives if used on these Alternators.

 

 

But the limitations of an AGM is not just about how fussy they are on the current going in, but prone to degradation when you take it out.

It is only in the last 12 months or so that we have begun to see indications that current and, continuous draw of it, is as big an issue as charging.

 

 

Many thanks Allan for explaining how the alternator functions (or should function) with respect to the charging of AGM batteries.

 

One would like to think that MH converters who supply AGM leisure/starter batteries as original equipment, ensure that an ECU controlled alternator is included in the package.

 

I seem to remember that manufacturers of AGM batteries have warned against the unsuitability of retrofitting these batteries unless both charging systems are compatible.

 

As you mention, Allan, it's just as important to consider what goes out in terms of rate of discharge. Type of use undoubtedly has a significant bearing on longevity, as mentioned by Brian.

 

Interesting times ahead B-)