Technical - Alternator or Inverter charging?

[weldted]

Hi we have an 2012 Elddis Aspire, 300 watts solar, 2 100 amp batteries. We also have a 2000 watt inverter which runs of the engine battery. Taking into account the low sun at this time of the year would I get any benifit when driving to switch on the inverter to power the onboard charger against just relying on the alternator to top up the leisure batteries. How the inverter is connected to the vans electrics as follows.

The output lead from the inverter has the 16 amp blue trailing socket and is plugged into the vans ehu socket, that way there is no possibility of having the inverter and mains both live at the same time, no switching over etc. Normaly if the inverter is used the mains charger is off and the aes fridge is on gas.

This system has worked fine for over four years and had the same set up on previous vans.

[aandncaravan]

What an interesting concept.

 

In theory the Alternator should be able to charge the habitation batteries at the maximum charge rate commensurate with optimum life.

However, some Motorhome manufacturers installations of Alternator charging are woeful.

 

 

So while what you propose won't be efficient, up to 40% loss in the Inverter and another 20% in the mains charger, it could still result in quite a bit of a boost compared to the normal Elddis Alternator charging.

 

But that will depend on how good the mains charger is, some of the early BCA units are not great chargers as they output only 13.8v when you really want 14.4v?

 

If your existing mains charger isn't up to it and you want to pursue this approach, a Sargent PX300 mains charger connected straight to the Habitation area batteries would be a cost effective option. On ebay and Amazon at about £95?

 

 

 

[weldted]

Just the man I wanted to hear from, when I first plug in ehu the voltage on the panel shows 14.4, depending on the state of the batteries this will then fall to 13.4. I belive the mains charger is rated at 20 amps max.

I have 300 watts of Solar panels with a blue point mttp controller which you have advised me on before.

It was just a query as to if I would gain more although not the most efficient way to charge the batteries amps is amps.

[aandncaravan]

Then you have a good charger.

 

When I say it is less efficient, it will just make the Alternator work that tiny bit harder, not a big deal.

 

Give it a go and report what back you see, as for some it might be a better way to boost Habitation battery charging on the move than an Intelligent Alternator powered charger?

 

Remember it must be a decent Inverter, suitable for powering sensitive electronics.

 

[Tracker]

Interesting concept?

 

Weldted says, unless I have misunderstood, that the inverter powers the hab electrics via the external ehu point, in which case driving with the inverter plugged into an external socket via a trailing lead would not appeal to me?

 

Many vans switch off or disable the hab electrics when the engine is running which might, or might not, include the built in charger?

 

How about using a free standing charger powered internally from the aternator driven inverter but I wonder if using the inverter and the alternator to charge the same batteries at the same time, however you do it, might throw up other complications and incompatibilities?

 

Alan often warns us of asking the alternator to do too much and I wonder if asking it to charge three batteries is risking overload?

 

It all seems a bit overly complicated to me, but good luck with it if it does work!

[Brian Kirby]

aandncaravan - 2017-12-15 2:26 PM..........................So while what you propose won't be efficient, up to 40% loss in the Inverter and another 20% in the mains charger, it could still result in quite a bit of a boost compared to the normal Elddis Alternator charging...............................

Are you sure about this, Allan? Apart from Tracker's reservation about driving the inverter via an external trailing lead inserted into the EHU plug (which I share), what is the actual source of the electrical power that will be fed to the inverter?

 

There is (if 2 x 100Ah batteries are operated to 50% DoD), 100Ah of battery capacity to replace. Surely the alternator (which appears to me to be the only source of 12V power to the inverter), will charge the leisure batteries more efficiently than taking its output up to 230V of simulated A/C via the inverter (but is the battery charger sensitive to sine or square wave A/C?), feed it into a battery charger, rectify it, and then feed the result back to the leisure batteries at 13 - 14 Volts?

 

It just seems a bit like scratching one' left ear with one's right hand to me, with considerable efficiency losses to boot. If the charging wiring to the 2 x 100Ah batteries is limiting the direct input from the alternator, wouldn't it be neater, and more efficient, to just beef up or duplicate that wiring to get the best the alternator can supply, rather than going via the step-up, step-down, inefficiencies?

[weldted]

I thought this might result in some mixed opinions, on my van the input socket for the 240 supply is in a locker which has room for the trailing lead from the inverter so nothing is mounted on the outside or the van. When the engine is running the 12 volt supply in disconnected to the van except the 12 volt for the ses fridge and the Alde heating allowing it to be used on the move ( with a securimotion regulator) no 240 supplies are disabled. The hab battery cabling is 12 mm, the cabling from the starter battery to pure sine wave inverter is 16 mm with a 50cm run. I have a 125 amp alternator. I would think the loading is not much greater than a B2B charger.

[Alanb]

I suppose that the attraction of the proposed method of charging is that the inverter is already installed, however in general I agree with Brian that it would be rather inefficient. My preference would be to resize the charging cables and split charge relay, so as to increase the charging current without adding unnecessary load to the alternator. In support of this approach may I quote Allan of A and N Caravans, in a concurrent thread relating to B2Bs. Allan is in turn quoting Velotron from an earlier thread relating to B2Bs.

 

The expense of a voltage sensitive relay, as used by Velotron is not essential, as a high current relay operated from the 12V fridge element supply would suffice, however the inclusion of a VCR keeps the charging circuit simple.

 

 

" One of the last posts was from the highly respected Velotron, who wrote

 

"Lots of marketing BS on the Sterling power website re B2B's!"

 

and

 

"A far cheaper option to the B2B for poorly wired vans is a length of 4AWG welding cable and a voltage sensitive relay. Just wire this in via a fuse direct from the van battery to your LB's (remembering to disable the vans built in charging system), and you will see 90% of the benefits of the B2B with none of the negatives and save yourself a pile of cash. With the new van, if I did not already have the B2B then I suspect this would have been my route. When I sold the old van, this is exactly the system that I put in it in place of the sterling B2B".

 

 

He has fitted better cabling and relays, just as we suggest, and quotes 90% of the benefits of a B2B with very low outlay.

 

Those figures show just how far off the mark the claims of even 2 times faster charging for a B2B are on a well set up system."

 

 

Alan

[Tracker]

Like so many, the bane of our lives in non ehu winter camping was always keeping leisure batteries topped up so any new or inovative and cost effective ways of doing this would have always been welcomed.

 

Sitting in the dark because the hab lights are disabled whilst the engine is running trying to whack some charge back into the hab battery soon loses it's appeal, especially given the abysmally low charge rate that the wiring allows through from the alternator to the hab battery!

 

If a battery is charged from two sources simultaneously, like solar and alternator, or solar and mains charger, or alternator and mains charger does the target battery get the benefit of both charge currents in full or does a voltage sensor somewhere sense the raised voltage from two sources and cut back the amps charged?

[Brian Kirby]

I will conjecture that charging from two sources, where one source is an alternator, needs detailed knowledge of both sources. If I remember, the greatest flaw of alternators, but also their greatest strength, is that they have the capacity to generate increasing current until they burn out. This tendency is controlled by restricting the current in the field coil. They generate more electricity than dynamos, at lower revs, but if the control module fails the output can run away. The control module varies the alternator output according to the connected load, so with zero load connected the alternator essentially produces nothing, and with a load rising to its maximum output, or more, its output will rise progressively to 100% of its potential. So, feeding its output to a discharged battery allows it to charge the battery at a relatively high rate initially, falling as the battery gains charge and its resistance rises.

 

I have no idea how pairing that charge with another, from a completely independent, but inevitably also controlled, source might work, but having two independent sets of controls acting on a single system can result in a "fight" between the two control systems, as each tries to read the system, varying its output accordingly, while the other does the opposite. Strange, and unpredictable, effects can result!

 

I'm not remotely expert in this field, so only speak from vicarious experience gained while working with systems engineers before I retired. I know it can be done, but both control systems must be compatible with each other. Tread with caution, I think, at least until expert advice is available.

[aandncaravan]

Brian Tracker and AlanB, Many people already have multiple chargers working at any one time with Solar and Alternator, Solar and Mains, etc.

The impact one has on the other will depend on the chargers involved.

 

But as it's already a potential issue for Weldted it shouldn't be considered a block to trying something, different.

 

 

As for inefficiency, the difference in amps consumed by using an Inverter is tiny, as I acknowledge above.

 

If you assume Weldted's battery bank normally takes 20amps from the Alternator to charge the habitation battery, throwing in to the mix a 60% efficiency rating for the Inverter and 20% loss in the mains charger, is still a small 'additional' draw in amps from the Alternator.

Probably no more than 10amps peak extra draw which isn't going to be noticed anywhere on a 125amp Alternator.

 

 

The mains charger is likely to deliver a full 14.4v directly to the batteries, that voltage and current is likely to be close to or higher than modified Elddis Alternator wiring will deliver. And without the hassle of carrying it out.

 

Plus it will drop to 13.5v and almost zero draw on the Inverter when the batteries are up to charge, not carry on at 14.4v for an entire journey like an Alternator does.

Few Alternators drop to 13.8v, once the battery is fully charged.

 

 

Weldted has a quality, neat install already in place, it might be unorthodox, but I can't see he has anything to lose by testing it out.

Praise to him for thinking outside the box.

 

Only potential issue might be with an AES Fridge deciding it would rather operate on the Inverters 230v rather than the vehicles 12v, dependent on it's priority algorithm?

But then again we are only talking 25amps'ish the Inverter will draw from the Alternator which won't be that different to the normal 14 amps/12v of the usual Alternator drain.

 

At least on 230v the Thermostat will be brought in to play on most Fridges. It might actually end up more efficient overall as the Thermostat may cause the Fridge to 'Off' for 50% of the time when it reaches it's set temperature?

 

 

AlanB, we would suggest the uprating of Alternator charging is done via the guidance on our webpage we publish in that thread, not via a VSR or Fridge relay driver.

We suggest the original relay should be used to drive the uprated 100amp relay, for the reasons specified in the text on the webpage : http://www.aandncaravanservices.co.uk/add-a-second-battery.php

 

 

 

[weldted]

My first trial will involve the ses fridge manually selected to 240 volt to allow the temperature control to operate so given the time of year reduce the demand for cooling, against the 12 volt running continuously.

Then switch to gas when parked up. Although I have the 130 engine, I have fitted the heavier duty 160 starter battery, I also have a system in place to measure the in and output of amps from the battery.

 

Many thanks again for your posts will update as I go.

[Brian Kirby]

Thanks for that further explanation, Allan. Sounds as though Ted has a good scheme up his sleeve! Since the fridge is MES he can choose the inverter output, as he says, so should benefit from the thermostatic control of its relatively modest consumption. He'll just have to remember to turn the kettle off before he hits the road! :-D

[Tracker]

Brian Kirby - 2017-12-16 10:13 AM

 

He'll just have to remember to turn the kettle off before he hits the road!

 

 

And make the big decision whether to turn the gas off too!

[thomsonjuk]

I would love to know how welted managed to get 2 110a batteries in a 2012 elddis did you remove the existing battery box and replace with something else?

[weldted]

Fitted LPG tank under the bathroom floor, freed up the gas locker, made up a vented box for battery in there, locker now holds 2nd hab battery, ramps, ehu lead, jumper leads, and all the must have extras.

Ran 12mm cables across to 1st battery in original locker with the + supply to no 1 battery and the - supply to no 2 battery. This balances the charge. If + & - are connected to the first battery and then cables just run to second battery uneven charge may result. Hope I explained that right?

 

Early test today with batteries around 80% showed engine charge at 1000 rpm at 7.3 amps switched on inverter rose to 11.1 amp going into battery,

[Brian Kirby]

Tracker - 2017-12-16 10:49 AM............. And make the big decision whether to turn the gas off too!

Bum! :-D

[Brian Kirby]

weldted - 2017-12-16 3:49 PM.......................Early test today with batteries around 80% showed engine charge at 1000 rpm at 7.3 amps switched on inverter rose to 11.1 amp going into battery,

Sounds even more as though you have a good scheme up your sleeve! :-)

[Tracker]

Brian Kirby - 2017-12-16 5:53 PM

 

weldted - 2017-12-16 3:49 PM.......................Early test today with batteries around 80% showed engine charge at 1000 rpm at 7.3 amps switched on inverter rose to 11.1 amp going into battery,

Sounds even more as though you have a good scheme up your sleeve! :-)

 

Having the knowledge and ability to figure it out and overcome all the little challenges one finds along the way must help - good luck Ted - hope it all works for you.

[weldted]

Next test. Van on drive not plugged into ehu for 48 hrs, lights, tv, Alde heating left on for 24 hrs.

Overcast and rain input from 300 watt solar minimal, batteries show 48% Engine started run up to 1000 rpm,

Input to batteries 16.4 amps, switched on inverter charge into batteries 23.7 amps, revs dropped a little perhaps but recovered, after 20 mins charging rate into batteries dropped to 20.1 amps, then began slowly to fall steadied at 18 amps after 60 mins down to 14.3 amps battery state shows 73%. Turned everything off. No discernible heat from wiring, batteries cold to touch. Voltage showing 13.1 volts after a further hour of rest. During this test ses fridge was off. Increasing revs made no difference to charging rate.

 

Next test will be a 6 hour run down to Homps, Aude.

[aandncaravan]

That sounds to me like you have a winning system set-up that is also more flexibly than a conventional B2B, especially with regard to Fridge running.

 

 

Can we suggest you don't regularly take the batteries to 48% Depth of Discharge (DOD) as it will shorten their life significantly.

 

The chart below from Exide on their 80Ah Gel range has over 1,000 cycles when discharged only 25% DOD, 750 cycles at 50% DOD and a measly 460 cycles at 80% DOD.

In other words, half the cycle life if deeply discharged, on a battery that is designed to discharge deeply!!!.

 

A budget battery will suffer to a greater proportion.

 

 

 

 

 

 

[weldted]

Hi, I appreciate the comment re the battery discharge, I do not normally allow this it was only done to get a better reading of what could be achieved with a battery discharged to 50%. Further test was a run around for approx 90 minutes, which brought them up to 94% charged. Charging rate had fallen to 4.3 amps from engine 6.7 with inverter on with engine running, 3.7 engine stopped and inverter still running. Controller is set to cut out at 30 amps charge or in excess of 14.7 volts. So not allowing more than around 15% charge of the batteries capacity, or prolonged higher voltage to avoid gassing. In reality I doubt either of these ranges would be achieved. I turned the ses fridge to mains voltage at the end of the test, with engine at 1,000 revs, engine revs again dropped slightly but recovered, charging rate increased slightly. I would probably not run the fridge on the inverter if the batteries were less than 80% so not to put too higher load on the alternator

But quite happily do so above this as the output seems well within the capability of my system. Only time will tell,

[weldted]

Oops!! Engine at 1000rpm not 100

 

(Edited: WeldTed, I have edited your original post, but for future reference you can edit your own posts within 30 minutes of posting. Keithl.)

[weldted]

Sorry? What needed editing and thank you for doing it

[Keithl]

weldted - 2017-12-19 10:34 PM

 

Sorry? What needed editing and thank you for doing it

 

weldted - 2017-12-18 4:04 PM

 

Oops!! Engine at 1000rpm not 100

 

All I was saying was that as you had spotted your mistake within the 30 minute editing window you could have gone back and changed your original post rather than add a second post pointing out your error.

 

Keith.