Leisure battery charging while driving

[Stevierox]

Hi, my leisure battery doesn't seem to get charged when driving! I've checked what i know but has anyone had the same problem with a benimar mileo 201 2020? Many thanks

 

[roadwarrior]

What "appears" to being said here is that the smart alternator can't cope with the load being asked for by the fridge, although I have no idea what offset the load means either, what I will say is my large fridge works excellently during travel,that is one area I'm not concerned about ironically. Previous fridges in previous vans all non smart proved to be not able to maintain temperature on long journeys and was the accepted norm, so I was delighted to discover amidst the charging woes that my big fridge worked perfectly on journeys. Are you saying the fridge takes so much power there is nothing left to charge the batteries? I'm tempted to think otherwise as when my auto electrician visited he showed 3 amps going to the leasure batteries and the fridge wasnt even on.and 14.4 was being sent to the engine battery at the time. A case of feast and famine. As many have said the smart alternator was never intended for motorhoming and it's different needs.

 

[roadwarrior]

Also I'm rather confused over fitment of a b2b being fitted to the starter battery as it's been stated the smart alternator keeps the starter battery with only enough charge to start (around 12.6) does a b2b somehow boost the voltage to 13.6 to the leasure batteries ?

 

[Lenny HB]

does a b2b somehow boost the voltage to 13.6 to the leasure batteries ?

Yes boosts it to 14.4 or whatever is suitable for the type of battery.
I think by doing so it tricks the alternator into working.
autorouter will know.

 

[autorouter]

The smart alternator might decide that the starter battery at 12.5V is charged enough, so it won't increase the voltage above that. It will provide any amount of power, but only at that voltage. So the lights, wipers etc all work fine. And from what you say, the fridge works fine on that voltage too, as it should. But if you connect a leisure battery to it with a standard split charge relay, it will only get charged up to 12.5V.

A B2B charger will take that 12.5V power, and boost it to whatever it thinks the leisure battery needs - 14.4V or 13.4V for example. That's why some kind of B2B is essential for a leisure battery with a smart alternator. It's a good upgrade for a non-smart alternator too.

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[Landy Andy]

It's a good upgrade for a non-smart alternator too

Why if you don’t have a smart alternator?

 

[Lenny HB]

Why if you don’t have a smart alternator?

Increases the charging rate to the leisure battery by a large factor. You can get B2B's with charge rates from 30 amps upto 90 amps.

 

[pete4x4]

A B2B is connected to the starter battery and boosts the voltage to a constant independent of the starter battery. This charges the leisure battery at its desired profile. A smart alternator will detect that the starter battery is losing capacity and will increase charge to the starter battery accordingly.

 

[autorouter]

Why if you don’t have a smart alternator?

What Lenny HB says. Also if the leisure battery is a different type to the starter battery (gel, AGM etc) then it can apply a suitable charging profile at the correct voltage. It's not as good as EHU or solar because it usually isn't sustained for the number of hours that the extended absorption stage of a gel battery requires, but it has a jolly good stab at it.

 

[roadwarrior]

This is gripping stuff...

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[roadwarrior]

Well I turned on my headlights on the m5 and it went up to 13.5 v which is what I found when I stopped the engine a couple of hours later

 

[Reallyretired]

My rapido was pathetic at charging the leisure battery if the fridge was on 12v without a smart alternator. I put it down to too thin wires and the batteries being 8m away from the alternator. The fridge was nearer and worked OK.

 

[Barti Ddu]

I suspect the OP is no longer monitoring this thread, but if he is, and as he has a 2020 Euro 6D Ducato based Benimar then I suspect he may well have a standard alternator rather than a smart one. A lot of Benimars are made by Autotrail (certainly PVCs are), and my 2021 Euro 6D Ducato based Autotrail PVC definitely doesn't have a smart alternator. In which case a lot of the discussion in this thread regarding smart alternators will have been sending him off on an unhelpful wild goose chase.

Thread '2021 Autotrail PVC - smart alternator?' https://www.motorhomefun.co.uk/forum/threads/2021-autotrail-pvc-smart-alternator.257871/

 

[roadwarrior]

I want to see it's not a fluke or coincidence but turning on the headlights did make it knock out 13.5 when I looked at it and the leasure batteries on the van control panel did read 12.9 when I parked up before using the hookup. If it holds true and this simple work round actually works then that is good enough for me - watch this space.

 

[roadwarrior]

i have been reading b2b chargers also have bigger cables going to the aux batteries, and that some feel that the heavier cables actually does most of the work - so where do the cables go from ?

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[autorouter]

have been reading b2b chargers also have bigger cables going to the aux batteries, and that some feel that the heavier cables actually does most of the work - so where do the cables go from ?

The standard method of charging a leisure battery is with a split charge relay. This relay is usually located inside the distribution fusebox. There is a wire from the starter battery to the fusebox, with a big fuse near the starter battery. There is a wire from the fusebox to the leisure battery, with a big fuse near the leisure battery. These two wires are very often a bit under-specified, especially in Brit MHs. They are adequate for safety/overheating, but can have a large voltage drop.

Some have found that simply replacing these wires with thicker ones boosts the amps going into the leisure battery, still using the split charge relay not a B2B. Especially if it's compared to one of the smaller B2Bs, like 30A. May be worth a try, before you buy a B2B.

 

[roadwarrior]

thank you - so now i have to find the fuse box that bridges the two battery types (starter +leasure) im ignoring for the moment i have 2 linked leisure batteries under my passenger seat, im assuming i need 2 cables from starter battery to fusebox and then 2 cables to the leasure battery

 

[Lenny HB]

thank you - so now i have to find the fuse box that bridges the two battery types (starter +leasure) im ignoring for the moment i have 2 linked leisure batteries under my passenger seat, im assuming i need 2 cables from starter battery to fusebox and then 2 cables to the leasure battery

Lesuire batteries will be connected in parallel so only one pair of cables to them.

 

[roadwarrior]

Sorry I meant 2 cables POS and negative from starter to fuse box and from fuse box to leisure

 

[movan]

Since reading this thread, I am panicking. . I don't understand a word of it. Serious question.... do I need to?

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[autorouter]

Since reading this thread, I am panicking. . I don't understand a word of it. Serious question.... do I need to?

No, not really. Most motorhomes charge the leisure battery at a reasonable rate while the engine is running.

If they are not getting charged, then you need to find out why, and fix it. But if it's working fine then no need to do anything.

Someone might add extra batteries, inverter, microwave, coffee machine etc, then wonder why the bigger batteries are not charging up fast enough. They can add a device called a B2B that boosts the charging rate when the engine is running. If you don't have that problem you can safely ignore it.

 

[pete4x4]

I have a Bailey motorhome, when I changed over to Lithium I realised I needed a B2B to charge the Lithium at the correct profile, I also realised that I did not want any of the B2B chage to power the fridge so I deliberatley isolated the lithium battery from the motorhome via a relay controlled by the D+ line.
Works great but what I did discover was that the existing split charge relay which now only powers the fridge when the engine is running had a max voltage of 13.1V when the alternator is putting out 14.1V so a very clear indication that the wire used is not man enough to deliver the current required but also why my lead acid batteries never fully charged whilst driving.

 

[ED O'DARAC]

No solar isn't the only answer or even an answer at all if you want/need big charge current on the road, B2B or charge booster is the way to go, solar is great when parked up especially if the sun shines

Hmm. I have B2B (Schaudt WA Booster) fitted as standard, (2022 Hymer Group van) but I have added 400 watts of solar wired directly to an EcoFlow Delta ('Power Station Lithium/MPPT Reg./2000w sinewave inverter). That is plugged through the 240v circuit so it always has plenty in reserve plus mains at all sockets. The EcoFlow is a game changer as it runs the van's charging system. Very neat and completely removable as it just sits in the garage. Possibly slightly more expensive than separate Lithium batteries plus inverter plus MPPT reg but SO SIMPLE, and it gives me a full second system. (And, I can run the fridge on mains whenever the sun shines) Each to their own, I guess.

 

[funflair]

Hmm. I have B2B (Schaudt WA Booster) fitted as standard, (2022 Hymer Group van) but I have added 400 watts of solar wired directly to an EcoFlow Delta ('Power Station Lithium/MPPT Reg./2000w sinewave inverter). That is plugged through the 240v circuit so it always has plenty in reserve plus mains at all sockets. The EcoFlow is a game changer as it runs the van's charging system. Very neat and completely removable as it just sits in the garage. Possibly slightly more expensive than separate Lithium batteries plus inverter plus MPPT reg but SO SIMPLE, and it gives me a full second system. (And, I can run the fridge on mains whenever the sun shines) Each to their own, I guess.

Interesting and "always more than one way to skin a cat" as they say so do you have the B2B and the solar running the EcoFlow or just solar? I guess you still have habitation batteries as well so are these charged with 240v from the EcoFlow? they look a decent bit of kit, which EcoFlow do you have?

 

[roadwarrior]

ok, so another 3 hour journey home with headlights on and off and watching cigarette lighter voltage ( so of course engine voltage with smart alternator ) to further my curiosity i will also fit a meter to the leasure batteries soon, but i am noticing after a period of time (say 30 mins) it drops to about 12.5/6 but if i put my headlights on after a few seconds it rises to about 13.4. of course if i slow down or brake it goes to about 15.1v. and then drops again to around 13.4. So I am happy about that, and assuming it continues I wont install B2B now as im quite happy to drive with my headlights on and save a few hundred quid . Im very aware this may not happen for everyone and im sure many will agree its not the perfect answer or the right answer, but for now in october as i ponder its usage till march next year its a result for me .

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[roadwarrior]

I want to test my 2x 100 amp lead acid batteries so first some basics please. I am told 12.6v is fully charged yes ?
I don't want to test to distruction,so what voltage do I drain to ? Maybe 11.6 v ?
I am thinking of using the onboard TV as a real world useful drain. Ironically due to trees I wont be able get a signal at home but I don't think that will matter to the TV - it will still consume the same amount of electricity I think and I will wait till it's raining or dark so the solar panel doesn't confuse things. One thing though, I know batteries recover if the drain is removed so I will just test the drain and the time taken and let you clever buggers determine the results.

 

[autorouter]

I prefer the approach of taking out 50% of the battery capacity, and seeing if the voltage settles to the 50% level, or more likely lower than 50%. Then you can calculate what the real capacity is. For that you need a chart showing the resting voltage of your type of battery against the percentage State Of Charge.

For example, a 100Ah, fully charged, with a 5A load for 10 hours (= 50Ah) should in theory be at the 50% level.
The voltage chart might indicate that it is in fact at the 40% level.
That means the 50Ah drain represents 100 - 40 = 60% of the real capacity.
The real capacity is (50 / 60) x 100 = 83 Ah.
So your 100Ah battery has lost capacity, and is behaving like an 83Ah battery.

 

[roadwarrior]

im sure you do but as i have no idea what 50% is or a chart i will go with my idiot test - it either copes or dies, i have a theoretical 200amps at my disposal so i will see what happens when i play a dvd in the tv later after dark.
i just took stock as thr sun is shining and my sargent screen says its 12.9v and is making an amp and draining 0.8 with nothing on (except the sargent) can that be right ?

 

[autorouter]

Here's a typical chart. Google 'battery voltage chart' for more. The exact values depend on the exact battery type, AGM and Gel are slightly higher. Note, this is the 'resting voltage', after a rest of an hour or two at least. Rest = no charge and no load.

 

[roadwarrior]

thank you,
i did a practical battery test today, i put the tv on which is rated at 24w at 10am today, with a starting voltage of 12.3v. The sun was shining but of course its winter sun so not as effective, and went down about 6pm anyway. Nonetheless after 11.5 hours the tv was still running and showing 11.9v and 12v after i turned off the tv. I am satisfied the batteries are ok if nothing else.

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[autorouter]

i did a practical battery test today, i put the tv on which is rated at 24w at 10am today, with a starting voltage of 12.3v. The sun was shining but of course its winter sun so not as effective, and went down about 6pm anyway. Nonetheless after 11.5 hours the tv was still running and showing 11.9v and 12v after i turned off the tv. I am satisfied the batteries are ok if nothing else.

24W from a 12V battery is 2A. 2A for 11.5 hours is 2 x 11.5 = 23 amp-hours. That is 11.5% of your nominal battery capacity of 200Ah.

From the chart, a drop from 12.3V to 12.0V represents a drain from 70% to 50%, ie a loss of 20% of the real capacity

So if 23Ah is 20% of the real capacity, then the real capacity is 23 / 20 x 100 = 115Ah. So your batteries, which were 200Ah capacity when new, are now behaving as if their capacity is only 115Ah.

Obviously this isn't an accurate test. The 2A consumption wasn't measured, it was estimated from the label. The voltages need to be measured more accurately, to two decimal places instead of only 1. And I picked that chart at random from the internet, so it may not be good for your batteries.