Do I need a B2B or can alternator cope?

[SteveandSueJ]

Currently have 110ah AGM hab battery. Considering going lithium, 100ah. Only off grid usually when travelling. CBE charger has gel setting so that is ok I believe. Victron solar charger for my 120w panel also ok. But do I really need a B2B or can my alternator handle charging when engine on. Have 3way fridge, 2009 fiat, 3ltr comformatic, 110ah van battery. Would current setup suffice? if not pls explain why I need B2B as struggling to understand... Thanks...

 

[Lenny HB]

You should always fit a B2B with Lithium not only does it give the correct charge profile for the battery it also protects the alternator.

Some CBE chargers have an automatic desulphation phase if yours has t's not suitable for Lithium.
Also if using EHU for more than the odd few night it is best to fit a mains charger with a Lithium profile.

 

[SteveandSueJ]

You should always fit a B2B with Lithium not only does it give the correct charge profile for the battery it also protects the alternator.

Some CBE chargers have an automatic desulphation phase if yours has t's not suitable for Lithium.
Also if using EHU for more than the odd few night it is best to fit a mains charger with a Lithium profile.

Thx Lenny. My CBE mains charger is the version that does not desulphate on gel setting. Would I damage the alternator if no B2B?

 

[Lenny HB]

Would I damage the alternator if no B2B?

Always a possibility I'd be more concerned about damaging the battery, if you are going to fit Lithium it's worth doing the job properly.

 

[MichaelT]

We had 200a lithium in our 2019 dethleffs that didn't have a B2B we just used gel setting and it worked absolutely fine, got about 18 to 20 amps. Now we have smart alternator we fitted a B2B. Gel is fine to charge on EHU for the odd day or so won't do any harm. Remember even with a B2B it's the alternator that charges/supplies power not the B2B!

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[MichaelT]

Always a possibility I'd be more concerned about damaging the battery, if you are going to fit Lithium it's worth doing the job properly.

Or save 500 quid.

 

[Just smiffy]

Just get two exide gels and double your capacity with no extra costs, your system is all ready…

 

[SteveandSueJ]

Or save 500 quid.

Well, tbh that is my concern if I have to fit a B2B. I can replace the AGM hab battery for 150 odd... Just watching the spend on what is an old van, but ticks all our boxes, apart from the hab battery limitation...

 

[MichaelT]

Well, tbh that is my concern if I have to fit a B2B. I can replace the AGM hab battery for 150 odd... Just watching the spend on what is an old van, but ticks all our boxes, apart from the hab battery limitation...

I've got a brand new 85a gel if interested

 

[Lenny HB]

My last van I got by with 3 x 80ah Gels, but the new van I decided to kit it out properly but I wouldn't spend what I've just spent (over £3k) on an older van.

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[SteveandSueJ]

I've got a brand new 85a gel if interested

Thx but need more AH. Current AGM is 110ah. But with inverter use charging ebikes and an odd day off grid has seen it drop to 12v so that has made me think I need most of 100ah from lithium or gotta buy 2 non lithium.... The B2B need could swing it one way or other. Rapido 4500kg so weight is fine...

 

[SteveandSueJ]

but I wouldn't spend what I've just spent (over £3k) on an older van.

Yep.... Gotta get the cost balance right.... Thx for advice, always appreciated...

 

[MichaelT]

Thx but need more AH. Current AGM is 110ah. But with inverter use charging ebikes and an odd day off grid has seen it drop to 12v so that has made me think I need most of 100ah from lithium or gotta buy 2 non lithium.... The B2B need could swing it one way or other. Rapido 4500kg so weight is fine...

Lithium then with good BMS and you should be fine. Fogstar got a sale on but other cheaper ones out there.

 

[Just smiffy]

Thx but need more AH. Current AGM is 110ah. But with inverter use charging ebikes and an odd day off grid has seen it drop to 12v so that has made me think I need most of 100ah from lithium or gotta buy 2 non lithium.... The B2B need could swing it one way or other. Rapido 4500kg so weight is fine...

An 85a gel will give you more useable amps then a 110a agm…

 

[SteveandSueJ]

An 85a gel will give you more useable amps then a 110a agm…

?? Sorry, how is that??? I thought AGM was better suited to hab usage...? Could you explain please?

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[Lenny HB]

?? Sorry, how is that??? I thought AGM was better suited to hab usage...? Could you explain please?

Don't really want to discharge an AGM below 59% a Gel can be discharged to 20%.
Also AGM are about the worst possible type of battery for habitation use.

 

[Just smiffy]

?? Sorry, how is that??? I thought AGM was better suited to hab usage...? Could you explain please?

As above….

 

[SteveandSueJ]

AHH, I see... That makes sense then... Thx for explaining.

 

[autorouter]

On the other hand, Gels are not the best for short high current loads like inverters. Ordinary flooded lead-acid (dual use starter/leisure batteries) can be better for that. Depends on your inverter use, do you charge two ebikes at the same time, or just one at a time? What wattage is your inverter?

 

[OldAgeTravellers]

We have a 2012 Hymer that suits us perfectly. Have looked about and just don’t like the newer vans with their problems, euro 6 etc. So, when the three Gels were not behaving as they did although they checked out ok I decided to study the Lithium upgrade. A lot will depend on how good at DIY you are and your ability to understand new technology, I am not trying to be condescending but there is a lot of techniques to learn which for some are second nature.
I fitted two 280Ah Fogstars, A Victron XS and a Victron 1200 VA Inverter. And built myself a RasPI GX. I also replaced the Hymer high curent cables and fitted appropriate High Current cables and fuses. I already had a Victron shunt. And I fitted a relay so as to keep the use of the Hymer panel above the door.
It wasn’t cheap, probably 2 to 3 times as much as changing the gels but I now have four times the capacity for less than half the weight. With the large Inverter they take up the same space. But the experience is fantastic, the wife loves them (tick) and the experience with our recent three months away was fantastic. They should last at least ten years probably 15 so that will see me to 90 years old. If I ever change the van it can all easily be removed and moved to the new van.
Use a good supplier like RogerIvy at Offgrid Solutions who you can trust and will help and advise with all the parts and read the many posts on here and elsewhere on the subject.
For us, very much worth the money and much cheaper than changing the motorhome.

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[AdrianChen]

Thx Lenny. My CBE mains charger is the version that does not desulphate on gel setting. Would I damage the alternator if no B2B?

It might get a bit hot if sitting at low engine speeds with a big draw from the Lithium, plus all of the vehicles demands (lights wipers radio etc), but I don't know what size alternator you have - low speeds mean less air passing through the engine compartment and alternator fans allowing the heat to build a bit more. The existing wiring from the alternator to the leisure battery would need to be checked, ours was 16mm, which would have been ok I guess albeit with a bit of voltage drop at higher amps, our existing CBE Split Charge Relay was a 70amp.

I wasn't sure what our Lithiums (460AH) would draw through the alternator and wiring when charging and how long it would take, so fitted a B2B to control it all.

 

[SteveandSueJ]

On the other hand, Gels are not the best for short high current loads like inverters. Ordinary flooded lead-acid (dual use starter/leisure batteries) can be better for that. Depends on your inverter use, do you charge two ebikes at the same time, or just one at a time? What wattage is your inverter?

Inverter is 1000w pure. Ebike chargers are fine, 400w each and both will run at same time (drains my agm 110ah battery quickly) but I charge them seperately for this reason. My usage is not large, but agm battery is old, did run low last time off grid so thinking to change it, may as well be lithium. Rapido owners group has some older vans like mine, 2009 3ltr, just dropped 100ah lithium in, cbe charger on gel is ok, I have victron mppt 15/75, 120w solar, and alternator charges fine as apparently, the cbe does have a b2b management element that is sufficient. This group are highly respected so thought to check in case I have missed something...

 

[dunnah01]

A second AGM if room is where my money would be. If you move around when touring the alternator and solar will be fine. If money is no object then go lithium but not really necessary. A B2B will mean you will have an extra comfort factor over alternator alone but probably not essential. It would work out at about 20 year break even fitting £3k worth of lithium rather than replacing AGM every couple of years

 

[OldAgeTravellers]

It would work out at about 20 year break even

Why do people always look at break even? Will you ever break even on your motorhome purchase? We fitted Expensive “In Roof” Solar panels & battery. I get a 10% return on my investment. I count that as good, better than most places and if electric prices go up I rub my hands with glee. If I survive 10 years then I am making money.
My Lithium system just works, we can quickly boil an electric kettle & make a toasted sandwich and the batteries are quickly recharged if on a journey. This saves a lot of gas so money but better is the convenience. If I count days away as hotel nights saved then my motorhome has made vast amounts of money but would I have booked 3 months in hotels in Scandinavia? I doubt it, I would have had a couple of weeks on a beach in wherever.
My Lithium system just works and no concerns about using power. We have just spent 90 days off grid except plugging in one night after two months because the solar regulator had been switching the the fridge to battery and we had not been motoring at all but the batteries had only got down to 20%.
My lithium system cost me about £2,000 and a bit of time, would I switch back to my three big heavy gels? No way. Plus the inverter which without the lithium I wouldn’t have dared to have.

 

[MichaelT]

A B2B will mean you will have an extra comfort factor over alternator alone but probably not essential.

The alternator powers the B2B and only benefit would be higher charge rate.

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[Tombola]

A B2B will mean you will have an extra comfort factor over alternator alone but probably not essential.

The alternator powers the B2B and only benefit would be higher charge rate.

Higher charge rate is good when you are talking lithium
aswell as

optimized charging for the lithium battery via the cab battery, by managing the power input from the vehicle's alternator, extending the battery life by ensuring proper charging cycles, maximizing power usage while driving for smart and non smart alternators and preventing potential damage to the alternator by regulating the charging current; its particularly important for lithium batteries which can be sensitive to improper charging patterns.
there there is bluetooth monitoring, remote switching etc etc

 

[Lenny HB]

The alternator powers the B2B and only benefit would be higher charge rate.

It regulates the power supplied to the battery, Lithium batteries can charge at 100 to 200 amps or more without a B2B you are in danger of over loading the alternator particularly with the engine on tickover when the alternator is not getting enough cooling.

 

[dunnah01]

I get the Lithium thing but not for just charging ebikes on a non dpf Moho where if your batteries are below about 40% and you really need to go for a bike ride you can just run the engine for a little while

 

[Lenny HB]

you can just run the engine for a little while

Last thing you want to do with a modern diesel unless you like very expensive repair bills.

 

[MichaelT]

It regulates the power supplied to the battery, Lithium batteries can charge at 100 to 200 amps or more without a B2B you are in danger of over loading the alternator particularly with the engine on tickover when the alternator is not getting enough cooling.

If your set up can only give out 18 or 20a then no danger of the battery pulling 100 or 200 is there? And unless you're on the M25 its unlikely you'll be sitting idling for long?

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