24 volt Cab

[Mike001]

so I have fitted a 40amp B2B from the 24volt cab battery,
On testing with everything turned on that could be turned on, (simulating driving at night on a cold wet night), the charge voltage is just over 27 volts.
Is this acceptable? with daytime running the charge voltage is around 28volts.

 

[funflair]

I assume that your leisure batteries are 24v as well, is so I would think those voltages are about right as they seem to be basically double of what would be acceptable for 12v B2B.

 

[St3v3]

Have you set the b2b to match your battery type? What are they? What stage of charge are you in?

 

[autorouter]

Is this B2B working from a 24V alternator/cab battery system, charging a 12V leisure battery? When you say it's 40A, is that 40A input (at 24V) or 40A output (at 12V)?

To answer the question, the input voltage of the B2B doesn't really matter, the electronics should take that voltage and boost/reduce it to give an output voltage and current which is exactly what the leisure battery requires. For example a 27V and 21.5A input would be modified to give out a 14.5V output at 40A into the leisure battery.

 

[Mike001]

Sorry, a bit more info.
The house battery is a 12 volt400ah Lithium. Truck battery is 24volt wet. Both batteries fully charged.
Yep the b2b is set to lithium.
My concern is that I am not overloading the truck battery / alternator by dragging down the charge voltage,
The b2b is taking just over 20 amps from the truck (due to overheads). It is definately pushing 40amps the the lithium.
All I am thinking is that if the charge voltage drop is a bit too much with everything on, then I will fit an 80amp relay to switch OFF the b2b when I turn the vehicle lights on.
Would like to avoid that if I can tho.

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[Raul]

Read autorouter’ s post above, the voltage at the imput of the b2b does not matter for the purpose of charging your leisure lithium. The b2b will convert that voltage, and deliver the right voltage set.
When you switch loads on the cab side, it’s normal to have some voltage sag, and if you switch them of then voltage rises, tells you the starter battery it’s full, and voltage climbs.
And it’s not taking charge from the battery, but alternator. Unless the b2b is active with the engine off.

 

[Mike001]

Yep, I understand how the b2b's work.
Just checking that I wasn't overloading the 24volt charging side of things.