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Over-engineering on the electrics?
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userStuartO
Posted: 5 January 2019 12:33 PM
Subject: Over-engineering on the electrics?
 
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I'm a bit of a sucker for gadgets and I have probably gone too far (and added unnecessary weight) by over-egging things. For example I fitted a low voltage cut-off device to an accessory circuit which served only a single usb socket; the aim was to save the leisure battery from deep discharge - but the demand current was well under 3 amps and the leakage draw merely one small LED indicator, so it was very much into the realms of fancy waistcoats and I have since taken the device out.

But one of my fancy ideas (based on ideas put forward on this forum) was to optimise the service life of my leisure batteries by switching off the solar panels when in storage (to avoid unnecessary daily recharging) and instead to connect an EHU on a timer, to charge for a 12 hour period once per fortnight. This EHU arrangement results in discharge of the leisure batteries between charging periods of about 15 ampere hours, so I am shallow cycling the batteries by this amount as opposed to applying a charging voltage of about 14.3 for a few hours each day.

So which of these options is best for the service life of the batteries? Daily application of 14.3 volts on most days for a short period (usually very short or sometimes not at all in winter) but never discharging the batteries significantly, or applying and EHU charge once per fortnight, thereby subjecting the batteries to a recharge of around 15 ampere hours? The batteries are by the way a pair of varta LFD 90s.
useraandncaravan
Posted: 5 January 2019 2:32 PM
Subject: RE: Over-engineering on the electrics?
 
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Location: Conwy, North Wales


StuartO - 2019-01-05 12:33 PM

I'm a bit of a sucker for gadgets and I have probably gone too far (and added unnecessary weight) by over-egging things. For example I fitted a low voltage cut-off device to an accessory circuit which served only a single usb socket; the aim was to save the leisure battery from deep discharge - but the demand current was well under 3 amps and the leakage draw merely one small LED indicator, so it was very much into the realms of fancy waistcoats and I have since taken the device out.

But one of my fancy ideas (based on ideas put forward on this forum) was to optimise the service life of my leisure batteries by switching off the solar panels when in storage (to avoid unnecessary daily recharging) and instead to connect an EHU on a timer, to charge for a 12 hour period once per fortnight. This EHU arrangement results in discharge of the leisure batteries between charging periods of about 15 ampere hours, so I am shallow cycling the batteries by this amount as opposed to applying a charging voltage of about 14.3 for a few hours each day.

So which of these options is best for the service life of the batteries? Daily application of 14.3 volts on most days for a short period (usually very short or sometimes not at all in winter) but never discharging the batteries significantly, or applying and EHU charge once per fortnight, thereby subjecting the batteries to a recharge of around 15 ampere hours? The batteries are by the way a pair of varta LFD 90s.


A lot will depend on the battery temperature, as when the batteries are cold they will take a higher voltage.
This time of year a 100w, well set up Solar panel will struggle to deliver more than about 4Ah a day so it just doesn't have the power to do much damage. Probably doesn't even have enough power to keep the batteries topped up. Even if it can reach 14.4v

In mid June/July it will be a very different picture.as not only will the batteries be warmer but the days much, much longer and the Sun higher in the sky.


Clearly using EHU and replacing 15Ah per 2 weeks (is that 7.5 ah from each battery?) isn't going to use up much cycle life, but does suggest that you maybe want to shorten the charging interval to one week?.


I wonder if the ideal in your case might be to isolate the batteries?
Healthy Varta LFD90's that have had their battery clamps removed, stay charged for up to 6 months, but a 3 month charge is a good idea.



Stuart has gone to a lot of trouble to look after his batteries.
The owner of the battery below didn't.
Just left his on unattended long term EHU and the charger faulted, see the photo of his exploded battery below.

The owner has just bought, literally today, an Elektroblock EBL 220 because the old one was destroyed by the Acid, as were a lot of surrounding things..
He has a lot of time and expense ahead of him cleaning up the acid mess and replacing all that is beyond restoration.


Edit -
I can't resize the photo, for some reason my editing software won't work, sorry. I have temporarily added it to the top of our battery FAQ page : http://www.aandncaravanservices.co.uk/general-battery-faq.php



Edited by aandncaravan 2019-01-05 2:58 PM




(Varta battery exploded small.JPG)



Attachments
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Attachments Varta battery exploded small.JPG (52KB - 46 downloads)
userStuartO
Posted: 5 January 2019 2:48 PM
Subject: RE: Over-engineering on the electrics?
 
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I have in the past, with a pair of Exide Gel leisure batteries, simply left an EHU connected all winter when in storage - and the batteries lasted over 10 years and were by no means completely knackered when I decidied it was time to change them. But the MH was then in a garage so I didn't get any solar output; maybe that would have had an impact if the MH was parked outdoors.

Now that I have to store outdoors and have witnessed the 15 ah per fortnight drain which needs replacing, might I not just as well leave the EHU continuously connected? Is the charger in an EBL101 going to be troubled by that? Will a pair of Varta LFD90s really be at risk ofexploding if I do?
userCharles
Posted: 5 January 2019 3:05 PM
Subject: RE: Over-engineering on the electrics?
 
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My Elddis charger is switched off. The leisure battery is on an optimate 2 maintainer 24hrs a day. It tops up the battery periodically at a nice safe 800ma
useraandncaravan
Posted: 5 January 2019 3:10 PM
Subject: RE: Over-engineering on the electrics?
 
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Stuart, The EBL101 won't be troubled by that and the Varta is particularly resilient when it comes to higher charge voltages, but what if the charger faults and doesn't 'step down' to it's 13.8v float charge, or worse does what has been seen last year with the Sargent Solar controllers where they start charging at 16v?

The customer, whose varta battery I just managed to post above, believes his charging system faulted, and he wasn't there to stop the damage being done.

There are two issues, one is about the damage to the batteries, the other is what happens if things go wrong?



Charles, the Optimate isn't just good because of the very low current, but because it spends half it's time asleep and testing the battery to ensure it delivers what is perfect for a battery on long term maintenance storage mode.
We wish all manufacturers would include a Optimate style safe 'Storage' float mode in all chargers.
The problem is that leaving batteries on charge when they don't need charging is a very British thing and the best charger manufacturers are in Holland, Germany, Italy, etc. and don't understand what an issue it is for the UK.
Only Victron have so far catered for it in their chargers.









Edited by aandncaravan 2019-01-05 3:24 PM
userplwsm2000
Posted: 5 January 2019 5:34 PM
Subject: RE: Over-engineering on the electrics?
 
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I considered a few options for long term EHU.

I looked at the Optimate 2, but it didn't meet all of my needs for 2 reasons - 1) It only maintains 1 battery so need another one for the starter battery. 2) My van is on my drive and we often just pop in to get something or use the fridge for extra storage etc. 800mA is a bit too low for this and I think 2Amp would have been more suitable for this scenario.

I also considered unplugging the solar panels and use a spare laptop power supply (giving about 19V at 3A) as a feed for the solar controller (Votronic duo). The EBL charger would also be unplugged. The Votronic can be set to give a lower trickle charge voltage around 13.3V and will trickle charge the starter battery too. It would also cope with the occasional 2-3 Amp demand without draining the battery. I wasn't able to get an answer from Votronic about running it with a continuous supply (rather than powering down each night).

I ended up by designing my own power supply/trickle charger that can give out 3A maximum. It also has a separate overvoltage protection in case something goes wrong (I sometimes have too much time on my hands ).

It would be great if there was more control on the EBL trickle voltage. I would also be slightly anxious at leaving the EBL charger on for months on end / year after year. I haven't looked inside an EBL but I would not be surprised to see electrolytic capacitors inside. In my experience, these have a tendency to "dry up" after prolonged periods of use (several years).

Edited by plwsm2000 2019-01-05 5:37 PM
userStuartO
Posted: 6 January 2019 9:35 AM
Subject: RE: Over-engineering on the electrics?
 
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I've put my MH back on to continuous EHU, so I will be relying on the Electroblock to settle back to a maintenance charge at 13.8 volts but I have also left the solar panels switched off, so that will prevent the applied voltage rising to 14.3 when the sun strikes the solar panels.

Ideally, following current best practice, in order to achieve the desireable maintenance voltage of 13.2 rather than 13.8 volts I suppose I would get the EBL101 modified to change its end-of-charge voltage - would that be possible? Would it simply require changing the value of a resistor or is the programming of the final voltage buried inside an integrated circuit device?

Edited by StuartO 2019-01-06 9:35 AM
useraandncaravan
Posted: 6 January 2019 12:19 PM
Subject: RE: Over-engineering on the electrics?
 
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Stuart, it is easy to modify the Schaudt chargers to have a lower Float charge voltage of 13.2v.
However, that would impact 'normal' charging enormously.

Most quality motorhome chargers use 'Timers' for the duration they charge at the higher 14.4v.
They do not work like Car chargers where the battery is charged for hours and hours at 14.4v until the battery 'tells' the charger it is 'full'.

A motorhome charges at 14.4v for a set time, typically 4 hours, before dropping to 13.8v to put in the rest of the charge, regardless of whether the battery is full or not.

So on a single 80Ah battery that is discharged to 50% DOD (40ah taken out) a typical charger will be able to put in an average 13 amps per hour, or a potential 52AH, before dropping to a slower 'trickle' charge to apply the rest of the charge.
Obviously for your 2 x 90Ah battery bank discharged to 50%DOD (90Ah taken out) much of the charge will be done at the lower 'trickle'/'Float' rate.
If you drop this to 13.2v a big battery setup probably won't ever get charged fully.


Why is it done this way?
On a multi stage Car charger it 'boost' charges at 14.4v until the current being taken by the battery drops below about 1 amp, at which point the charger drops down to 13.8v Float.
The problem is that if the battery is 'faulty' it may continue to draw more than 1 amp so never drop to the safer 13.8v Float.
Obviously charging a failing battery at 14.4v continuously for days is going to end in disaster. Which is why Car battery chargers almost always warn not to charge a battery unattended.

But also think about an overlarge battery bank on a Car style charger. If the charger was relying on the current draw to be below 2 amps as it's trigger to drop to 13.8v and each battery still draws 1 amp when 'full', that will be a total of 4 amps being taken from the charger which will never, ever drop to 13.8v.

By employing a 'safety' 4 hour, or whatever, Timer a Motorhome specific charger ensures that no matter the circumstances it will drop to the lower, safer 13.8v.


The above also demonstrates why/how mains chargers have a limit of the battery bank size then can effectively support, as 4 x 100Ah batteries on a 4 hour timer charger will take weeks to charge.
Probably never get fully charged, Sulphate prematurely and expire.


I suspect that your EBL might be one of the older ones that only had a 1 hour Timer for Wet batteries.


The best Solar chargers also often employ Timers for the same safety reasons : Starting the day at 14.4v for 1 - 4 hours then dropping down to 13.8v regardless of the battery charge state.
You will hear some people report that their Solar charger has replaced the overnight discharge by 'mid morning', when what they mean is the Solar charger has dropped to 13.8v by mid morning.
The battery could still be half full, but because they are applying Car Battery charging methodology to the Solar regulator, they think 13.8v means 'full'.


The newer CTEK's employ timers for safety, forcing the next stage in the multi stages, but they also have a final stage that 'tests' the battery and if it isn't charged fully, it starts the whole cycle again to have another go at exploding the battery.
If you have a CTEK, we suggest you treat it as you would a conventional Car charger and don't leave a battery unattended for long.
The most damage from a battery explosion we have ever seen was caused by a CTEK 'looking after' two motorhome batteries.
Because most of them are designed for single Car battery banks of about 80Ah, their 'Smart' capability doesn't always work as expected when hitched to 2 x 110Ah tired budget batteries.


Sorry Stuart, I know you are aware of most of this, just gone into it a bit more for other readers.







Edited by aandncaravan 2019-01-06 12:29 PM
userStuartO
Posted: 6 January 2019 1:12 PM
Subject: RE: Over-engineering on the electrics?
 
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aandncaravan - 2019-01-06 12:19 PM

Stuart, it is easy to modify the Schaudt chargers to have a lower Float charge voltage of 13.2v.
However, that would impact 'normal' charging enormously. ....

Sorry Stuart, I know you are aware of most of this, just gone into it a bit more for other readers.


No apology needed; I enjoyed reading what was a very useful tutorial and it explains a lot.

So for MH owners whose charging system is as good a Schaudt Electroblok, even an old one like mine, leaving it on EHU continuously while in storage will be best for service life as long as 13.8 volts won't damage the type of leisure batteries you have (which with Varta LFDs it won't?) but if you also have solar panels they should be switched off or disconnected, to avoid the potentially adverse effect of unnecessary applications of 14.3 volts.
userBruceM
Posted: 6 January 2019 2:49 PM
Subject: RE: Over-engineering on the electrics?
 
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StuartO - 2019-01-06 1:12 PM

. . . but if you also have solar panels they should be switched off or disconnected, to avoid the potentially adverse effect of unnecessary applications of 14.3 volts.


Unless we're using a votronic solar regulator??
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