B2B

[WildThingsKev]

I've had the Votronic 45A b2b charger installed in our Rapido for 5 or 6 years now. It is activated by the D+ signal and charges 2 110Ah Victron gel batteries. I previously had a solar panel installed but when fitting the b2b I added a relay to isolate the solar output from the batteries to avoid them competing. In fact, I often manually isolate the solar from the batteries the night before moving so the b2b gets the true picture when it starts up for the morning drive. This is especially important for gel batteries where the "surface charge" can be quite different to the real state of charge because of the thicker plates.



With our use pattern I wouldn't bother with a solar panel again. We are in the alps for the next 2 months and even though today is bluebird the 80w panel would probably have output less than10Ah all day as the sun disappears behind a mountain at 3pm.

I wired in the b2b with new thick wires between both batteries for optimum charging and it always knocks out the full 45A for an hour or two after several days in the cold.

Ps, never even heard the cooling fan running.

 

[hairydog]

there are different models. the LV is the usual one for the latest smart alternators. the standard version is the one for 'normal' alternators.

That's true, but you can use the LV with a standard alternator. You set it up so that it only runs when the ignition is on. You can get an LV one about £100 cheaper.

 

[hairydog]

The cabling between your alternator and the engine battery should be fine. On some motorhomes the cabling to the leisure system is suspect. On my Hymer there is a good sized cable running to the leisure system from the engine one, protected with a 50A fuse. Some peple say that it is British manufacturers that use lower rated cables but I can’t say one way or another. Adding a B2B will not overcome undersized cables if that is the problem.

On vehicles with SCR or VSR charging, something has to limit the current that runs between the batteries when the relay cuts in. A decent length of not-too-fat cable is ideal. Fit thicker cable and you will get burned out terminals, melted fuse holders and perhaps ruined batteries.

 

[Okta]

On vehicles with SCR or VSR charging, something has to limit the current that runs between the batteries when the relay cuts in. A decent length of not-too-fat cable is ideal. Fit thicker cable and you will get burned out terminals, melted fuse holders and perhaps ruined batteries.

On my Votronic BtoB I can set a limit on the input current as well as the output current, which I have set to be within the limits of the wiring relays and fuses. I would have thought that relying on the resistance in the cables would produce heat in them and that sounds a bit risky to me. However I am always ready to learn something new.

 

[hairydog]

On my Votronic BtoB I can set a limit on the input current as well as the output current, which I have set to be within the limits of the wiring relays and fuses. I would have thought that relying on the resistance in the cables would produce heat in them and that sounds a bit risky to me. However I am always ready to learn something new.

The cable resistance is indeed used to limit maximum current, and overheating isn't an issue: the heat is dissipated over a long length of cable.
With a B2B charger, the problem doesn't arise: this is only an issue when a relay joins the starter battery and alternator to the leisure bank, which will inevitably have a different state of charge. Huge inrush currents could result.