Selecting the correct product option dc to dc versus BMS CL 12/100

DIY
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1

I have a motorhome with both 12v and 24v alternators.24v are starter and 12 is for house batteries only Presently the house batteries are charged by the alternator, solar array and inverter charger I am switching from lead acid to lithium ,do I need a DC to DC charger from the 12 v alternator [ not connected to a starter battery] or use a BMS CL 12/100. Neither will have a starter battery so how can I wire it and which is the best option.
Can I interrupt the lead from the 12v alternator to the Lithiums 12v using the Victron product.

2

To use both the DC to DC or the BMS CL 12/200 you need to have a lead acid battery on the output of the 12V alternator. The DC to DC or BMS installs between the lead acid and the lithium. Look at the manuals for both these devices and they show a lead acid battery.

There are 2 reasons for this. The alternator needs a battery to act as a buffer to smooth out voltage control. Many people have tried without and report voltage and current cycling as there is nothing to moderate the system if the control systems in the alternator and charge control interact. Secondly, there is an issue called load dump, if the lithium battery is charging at high rate and the BMS disconnects the alternator can not respond quickly enough and the voltage can spike to 70V, blowing the alternator diodes plus other electrical equipment. The lead acid battery would need to be small, say 50Ah.

One way to deal with some of this is an external regulator such as the Wakespeed WS500 or Arco Zeus.

Another issue with the BMS is what voltage the alternator outputs, see BMS and alternator voltage

3

Thanks so much for the information. I was thinking of the Orion XS as a DC to DC until I read your message. To overcome this could I use an Orion 24v to 12v and not use the 12v alternator at all?
Thanks again
Steve

4

Yes, a 24V to 12V would work and it is buffeted by the engine start battery.

You can get alternator to battery chargers that do not need the buffer battery, they are more costly as they have extra circuitry to stop the voltage cycling. I do not know if lithium versions are available. Victron do not sell these.