b2b charger

[Wherearewenow]

hi all just trying to work out which b2b charger i will need ,there seems to be diffrent ones. victron do one but which amp one will i need to charge 2 x 110 ah batterys from main starter battery.thanks .i have a 90 ah as main starter battery ...thanks again ,

 

[paddymcc]

It really depends on how quickly you want to recharge. A 30A B2B will provide 30Ah if the engine is run for 1 hour, a 50A one will provide 50Ah. So you need to decide based on how much driving you do and how often against how much you use the LB. The starter battery size is irrelevant.
Also you need to look at the wiring in your system to decide if that needs replacing with bigger wires.

 

[Steve and Denise]

I have recently had this very conversation with a battery supplier after ordering a 300ah lithium, at the moment the std charging system will deliver 50ah to our leisure batteries via 16mm sq cable according to the display but the supplier suggests a 30ah B2B as not to overheat the 150amp alternator.
My last B2B was a sterling 45amp and I had no problems but that was on lead acid 330ah

 

[Wherearewenow]

lots of great advice on here ,thank you

 

[Kannon Fodda]

What is the charge rate that the batteries will support? That, and the capability of your alternator sets the upper limit. Below that is how long you want to be driving.

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[Carpmart]

It’s an interesting question. Judging by the Bluetooth stats I get 80A delivered to the lithium batteries with the motor running. Whilst on EHU or with the Gennie running I get 60A from the mains charger. Both seems to be working very well with just over 400A of lithium batteries.

I went for the ‘drop into existing set up’ approach when installing the lithium batteries, so I have not bothered looking at what is delivering the 80A with the motor running. Is the alternator up to delivering that (?)…. again no idea, but it’s working at the moment.

 

[autorouter]

hi all just trying to work out which b2b charger i will need ,there seems to be diffrent ones. victron do one but which amp one will i need to charge 2 x 110 ah batterys from main starter battery.thanks .i have a 90 ah as main starter battery ...thanks again ,

If they are not lithium batteries, the usual rule for maximum amps is Battery Capacity/5, so your 220Ah lot can take 220/5 = 44 amps.

All the batteries - leisure and starter - are charged from the alternator when the engine is running. A B2B will have some method of ensuring it only turns on when the engine is running and the alternator is charging. The B2B doesn't charge the starter battery, which charges direct from the alternator, so there's no need to take that into account.

 

[Steve and Denise]

Careful - Alternator Charging Lithium - Victron Energy

Charging lithium batteries from an alternator, be that in a boat or vehicle, presents some challenges when compared to the straightforward nature of charging lead based batteries. The video in this blog highlights these lithium challenges and shows you what can happen when things go wrong –...

www.victronenergy.com

Found this on the Victron site it would appear large lithium batteries can draw to much if not regulated

 

[Steve and Denise]

It’s an interesting question. Judging by the Bluetooth stats I get 80A delivered to the lithium batteries with the motor running. Whilst on EHU or with the Gennie running I get 60A from the mains charger. Both seems to be working very well with just over 400A of lithium batteries.

I went for the ‘drop into existing set up’ approach when installing the lithium batteries, so I have not bothered looking at what is delivering the 80A with the motor running. Is the alternator up to delivering that (?)…. again no idea, but it’s working at the moment.

Take a look at the Victron video I have an IR temp reader might pay to check at Lincoln this weekend.

 

[steveh57]

I have recently had this very conversation with a battery supplier after ordering a 300ah lithium, at the moment the std charging system will deliver 50ah to our leisure batteries via 16mm sq cable according to the display but the supplier suggests a 30ah B2B as not to overheat the 150amp alternator.
My last B2B was a sterling 45amp and I had no problems but that was on lead acid 330ah

Steve and Denise . Did your supplier suggest why the alternator would overheat on your existing circuit? If you have one 30a B2B and lose say 10-12A for the fridge whilst driving, it doesn't leave a lot leftover to re charge your Lithium, I'm just wondering for myself whether I can safely add another 30A B2B i.e 60A total without troubling the Alternator.

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[cmcardle75]

It’s an interesting question. Judging by the Bluetooth stats I get 80A delivered to the lithium batteries with the motor running.

Your 300Ah Lithium will be fine with that. Your alternator might not be, especially if sitting at the traffic lights with no airflow and potentially other drains also in evidence. Also, it might be over the split charge relay's rating.

 

[Steve and Denise]

Steve and Denise . Did your supplier suggest why the alternator would overheat on your existing circuit? If you have one 30a B2B and lose say 10-12A for the fridge whilst driving, it doesn't leave a lot leftover to re charge your Lithium, I'm just wondering for myself whether I can safely add another 30A B2B i.e 60A total without troubling the Alternator.

He said the lithium will take what it can if unregulated as I say 16sq mm cable fused at 50amp I think the fridge on auto takes its feed from the engine battery when the engine is running so would leave a full 30amp charge but I may get corrected still exploring options

 

[EuroTrotters]

What B2B for a 110ah alternator?

 

[DBK]

I have 2 * 95Ah batteries and fitted a Sterling 60A B2B. Knowing what I do now a 30A model might have been a wiser choice but its been in nearly three years now and nothing has blown up yet.

 

[Steve and Denise]

I have 2 * 95Ah batteries and fitted a Sterling 60A B2B. Knowing what I do now a 30A model might have been a wiser choice but its been in nearly three years now and nothing has blown up yet.

I would agree with you possibly ott for 190ah LA

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[autorouter]

I have a 70A B2B for my inverter lithium batteries (290Ah equivalent), and the fridge power is 14A in addition. The alternator is whatever Hymer put on a Fiat 2.8 engine, and it's worked fine so far. I usually drive with the headlamps on as well, even in daytime, and that's another 12A.

 

[Carpmart]

Take a look at the Victron video I have an IR temp reader might pay to check at Lincoln this weekend.

A good video (to a point) but it just sounds like they are pushing various Victron supplied products to solve the ‘problem’.

Fan generated airflow is only one aspect of cooling making this simulation fit specifically the purpose Victron wish to convey….would be interesting to see this test with simulated 55mph airflow on the alternator, if that creates ‘enough’ cooling at a representative cruising speed of 2000 RPM.

The only condition that concerns me having watched this is me starting the engine after a week off grid and idling for 20 mins whilst completing ‘pre flight checks’ etc where the batteries could overwork the alternator a ‘bit’!

 

[Steve and Denise]

Good point!

 

[gerry mcg]

What size of B2B Should I consider for 100-200Ah Lithium? 60A?
(Compressor fridge)

 

[Jamesh]

It really depends on how quickly you want to recharge. A 30A B2B will provide 30Ah if the engine is run for 1 hour, a 50A one will provide 50Ah. So you need to decide based on how much driving you do and how often against how much you use the LB. The starter battery size is irrelevant.
Also you need to look at the wiring in your system to decide if that needs replacing with bigger wires.

But the actual ah the battery charges at will be less due to energy conversion perhaps as much as 50%

Cheers James

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[paddymcc]

But the actual ah the battery charges at will be less due to energy conversion perhaps as much as 50%

Cheers James

Yes I should have said that is the theoretical maximum rate but in reality it will be less. Lead acid can't take as fast a charge as lithium for example - one of the advantages of lithium. It also depends on the state of charge of the battery, a nearly full LA will also take less than a lithium at the equivalent state of charge.

 

[autorouter]

But the actual ah the battery charges at will be less due to energy conversion perhaps as much as 50%

Actually the amps and hours when charging and discharging are about the same, even though the 'round trip' of fully charging and discharging is only about 70 to 80% efficient. Lead-acid batteries charge at about 14.5V, and discharge at about 12.5V, so a lot of the inefficiency is taken up by the voltage difference. The amp-hours is about the same for charging and discharging. There is some difference, but not as much as you might think.

Lithium are much more energy efficient, so the amp-hours in and out are about equal.

The only condition that concerns me having watched this is me starting the engine after a week off grid and idling for 20 mins whilst completing ‘pre flight checks’ etc where the batteries could overwork the alternator a ‘bit’!

Or what happened to me - starting off, then running straight into a traffic jam, stop-start for an hour in the mid-day heat. Definitely no 55mph airflow.

 

[Bolti]

How is a b2b wired?
One end on the leisure batteries obviously.
Is the other end connected to the alternator or starter battery or both?

 

[Carpmart]

How is a b2b wired?
One end on the leisure batteries obviously.
Is the other end connected to the alternator or starter battery or both?

 

[Bolti]

Thank you Carpmart.
Sorry but I am a bit dense, I see on the schematic that the positive wire travels straight across does this mean it needs to be on the same terminal as the alternator or can I use any of the connections on the positive plate?

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[Steve and Denise]

Any connection on the battery positive but must be fused

 

[EuroTrotters]

I have a 70A B2B for my inverter lithium batteries (290Ah equivalent), and the fridge power is 14A in addition. The alternator is whatever Hymer put on a Fiat 2.8 engine, and it's worked fine so far. I usually drive with the headlamps on as well, even in daytime, and that's another 12A.

I wish everyone drove with them on

 

[Steve and Denise]

Part of the attraction with lithium is the quick recharge time so I would prefer 50 or 60 amps rather than 30 amps if a 150 amp alternator will cope with that 300 by 30 = 10 hours 300 by 60 = 5 hours driving time if that’s correct

 

[autorouter]

Sorry but I am a bit dense, I see on the schematic that the positive wire travels straight across

This schematic is a bit oversimplified. The alternator to starter battery is a vital link, that causes all sorts of problems if it is ever disconnected. If there is a fuse on it, it is never combined with a fuse for other devices. Your B2B connection will go from the starter battery terminal plate. It needs its own fuse of a suitable size.

The B2B will have a method for only turning on when the alternator is charging, so it won't drain the starter battery. The alternator will be powering the B2B and also charging the starter battery if it needs it.