extra battery
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wildebus
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This is where a B2B can be very good for limiting the load on the alternator even when the leisure battries are low (or if you have Lithium, which will take a high current even when just a little down).
I run the Ablemail AMC 60A B2B which is good as internally it is a dual 30A unit and you can configure each half differently. I have one half only coming on initially and the other half once the alternator voltage increases a bit more to help straining the alternator at tickover speeds.
trevskoda
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Any link to the ablemail current regulator, sounds like a good cure.
wildebus
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Link on my shop is here - https://www.wildebus.com/product/ablemail-b2b-chargers/ .
Datasheet PDF is here - https://www.ablemail.co.uk/sites/default/files/specs/AMC12-12-60E DATA SHEET.pdf
Not a cheap option but very robust. I tested the 30A version on a 50% depleted 400Ah Lead Bank and it ran at full power continuously for around 4 hours (unlike some other brands that throttle back after a short time).
For people who like Victron kit, the Smart-Tr B2B is available at upto 30A, but these can be connected in Parallel and you could also configure them differently so one turns on after the other with a higher voltage. Not sure if any other makes support paralleling?
Derekoak
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Whether you have an alternator overload problem with adding a other battery to an extent depends on the thickness and length of the wiring.
I have 2x100ah lithium and an 120a alternator and 16mm wiring 3m long, return by chassis. This is with a victron cyrix lict battery combiner. I have never as yet seen more than 40ah instantly on bms switch on to one battery only dropping quickly to 35 and only 66a into both together. My fiat alternator seems to respond to double batteries by charging more but by no means not double charge. It is much quicker to charge my batteries this way than my previous 30 amp b2b, which charged at 30 for a short while then dropped away to a long tail. But a lot of that is the response of lead acid compared to lithium.
wildebus
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This might be of interest .... Difference in Charging profile between using a B2B Smart Charger and a simple Relay.
The batteries are the same (400Ah of Lead Acid depleted to 50% at the start of each run) and the supply is the same (120A set voltage supply acting as an alternator).
First a 30A B2B
BT - Ablemail V_C by David, on Flickr
And a HC Cargo (Bosch) VSR
BT - VSR V_C by David, on Flickr
The batteries are the same (400Ah of Lead Acid depleted to 50% at the start of each run) and the supply is the same (120A set voltage supply acting as an alternator).
First a 30A B2B
BT - Ablemail V_C by David, on Flickr
And a HC Cargo (Bosch) VSR
BT - VSR V_C by David, on Flickr
wildebus
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The most likely issue Compo would have in his scenario is not with the cabling, but the actual charging unit. A battery bank of that size is much larger than the recommended maximum and the charger could overheat as it would be running at its (very low) maximum for so long.
trevskoda
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Two things with my van is first, the alt is an old 75/90ah I think, second thing is its the old thin v belt where as the later iveco engines run the flat ribbed belt giving a better grip and with a 120ah alt, what happened is the mot chaps switched the batteries in and wore out the belt at tickover only to snap a few days later, me I don't switch them in until I'm well under way and at 2500rpm, I have never had a problem in 9 years to the dipstick got hold of it.
wildebus
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Sounds like a plan.
My B2B is voltage sensing as mentioned, but the sensing is not on the main supply cable like most VSRs or B2Bs, but on a voltage sense wire. I have that sense wire going though a switch by the dash like your switch is, and can have it switched on (so purely voltage sensing), ignition (so stops it kicking in if I am charging the starter battery from mains), or off so an override like you have.
Belts and Braces with the different programming, but I think it is a good idea to provide protect the original electrics which were not designed to have a big constant load stuffed on while also having charging on the go.
Derekoak
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I was suggesting that the cabling could be part of the solution to overuse of the alternator. I did not see it as the problem.
I would dispute that a modern alternator works in a more intelligent way than a 120a set voltage supply, so that your vsr test is not real world? For example if you repeated my test, one 100ah battery then a 2nd at the same Soc surely with a your voltage supply the current would nearly double restricted only by the cabling resistance. My alternator only allowed 50%?
Just Maybe a vsr works better with lithium. I certainly have a very fast recharge now, seemingly within safe limits, that would have cost me much more with a b2b.
My system reaches my full charge cut off point still at around 12a charge rate per battery.
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wildebus
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Derek, my reply is regarding the OPs question primarily. Hence my posting of charging profiles of Lead-Acid of a similar size back to that proposed - again,of Lead Acid batteries, if if he were to bypass the current charging setup. Not talking lithium.
I also never said an alternator works in a more intelligent way than a set power supply (what exactly have I said that has resulting is you disputing that claim? Where is that claim?).
Is it a real-world test? It is. I did the test and I am in the real-world. Is it a representative test of when driving? That is another matter - alternator outputs vary significantly. When driving especially. On a boat less so as they chug along at a constant speed often for hours unlike vehicles so it could be very representative of that.
Back to the OP question... It was actually specifically about using the existing charger and if it would cope with the extra battery. Cabling is not relevant as the output is so low to start with, the existing dual 4mm2 cable will be more than enough. Upgrading the cabling will do nothing as that is not the bottleneck in the system as it stands, the charger is.
Derekoak
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It was your graph that showed exactly what I think you would get if your 120a set voltage power supply . I do not think a real world alternator would give that result. So Compo does not have a set voltage power supply, he has whatever alternator in his vehicle. I suggest that is a significant difference and suggested that my results 1 battery then 2, not giving double current shows that your power supply acts differently than an alternator. So lithium in my case or not the relevancy is Compos setup.
About cabling the tone of the discussion was about overloading the alternator. I do not see that. I was saying that Compos cabling would control excess current. Certainly if his cabling is only 4mm it will surely? I was not suggesting upgrading cabling, that would increase strain on the alternator.
About cabling the tone of the discussion was about overloading the alternator. I do not see that. I was saying that Compos cabling would control excess current. Certainly if his cabling is only 4mm it will surely? I was not suggesting upgrading cabling, that would increase strain on the alternator.
Derekoak
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OK Compo did not say what his system was. I certainly would not add another lead to such a system myself.
It sounds to me that he should first remove the Sargent, then if his alternator is acceptable add a victron cyrix ct (lithium or not )depending on what he decides to do to uprate his batteries..
On 2nd thoughts I am not sure that a split charge relay is good for lead. Lead needs to be fully recharged ASAP and split charge relays do not do that reliably. Lithium is more forgiving in that way as it charges so easily. Perhaps vsrs are best with lithium.
I copied Phil with my new lithium system and there were many detractors saying that only a b2b system would work without destroying the alternator. Phil assured us that most modern alternators could easily cope. Having done my conversion I am pleased with what Phil suggested.
It sounds to me that he should first remove the Sargent, then if his alternator is acceptable add a victron cyrix ct (lithium or not )depending on what he decides to do to uprate his batteries..
On 2nd thoughts I am not sure that a split charge relay is good for lead. Lead needs to be fully recharged ASAP and split charge relays do not do that reliably. Lithium is more forgiving in that way as it charges so easily. Perhaps vsrs are best with lithium.
I copied Phil with my new lithium system and there were many detractors saying that only a b2b system would work without destroying the alternator. Phil assured us that most modern alternators could easily cope. Having done my conversion I am pleased with what Phil suggested.
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wildebus
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Nope. It is a self-contained unit which is really designed for caravans but been adopted by many British Motorhome manufacturers. I think the EBL was designed up-front as a more versatile unit.
The Sargent ECs are a good looking and tidy system but in most cases with very limited charging ability. When I check the output of my Sargent EC325, it peaked at 10A output - and at a set voltage which is not the best for long-term battery health.
I've kept the unit in place in my own. Motorhome for a number of reasons -
* It's 12V distribution and control I quite like, and it also controls distribution of the various 240V circuits,
* It provides the fresh and waste tank level info
If someone decided to just remove their Sargent, it would be a fairly complex thing to do as they would need to install a 12V distribution fusebox, together with a switch panel to turn various features (awning light, water pump, etc) on and off; a 240V consumer unit; and a tank monitoring setup as well. And then a new Mains charger and a split-charge setup. All of that is certainly doable for sure but little point while you have something in place that does most of it well.
I have bypassed both it's split-charge and AC leisure battery charging systems (very easy to do) - and it does still provide starter battery charging from EHU which can be handy sometimes.
trevskoda
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On 2nd thoughts I am not sure that a split charge relay is good for lead. Lead needs to be fully recharged ASAP and split charge relays do not do that reliably
How did you work that out, I can assure you my 200amp relay and a thick starter battery cable between starter batts and 2 less batts charges very fast, and with all connected together it acts as a big emergency engine start or jump start for helping others with a flat starter battery.
My van has still got the factory diode block in place which limits charging to 13.7 but once I flick the bypass relay switch I'm at 14.4 full welly.
How did you work that out, I can assure you my 200amp relay and a thick starter battery cable between starter batts and 2 less batts charges very fast, and with all connected together it acts as a big emergency engine start or jump start for helping others with a flat starter battery.
My van has still got the factory diode block in place which limits charging to 13.7 but once I flick the bypass relay switch I'm at 14.4 full welly.