12volt battery charging from a 48volt battery bank

[FloridaSun]

I'll propose that ANY MPPT controller with 60VDC solar input, would be fine to charge a 12V battery with. You must match the charger size to the battery & load size. PWM controllers "short" the input to the output, and a 48V battery has no inherent current limit that a PV panel has, so I would only expect the PWM controller to work for a few minutes before it fries something.
Sorry Naptown, I disagree with you here.

I was wondering about Naptown's response after reading this from the Tristar manual;

6.4.5 Minimum Diversion Load
The diversion load must be large enough to divert all the current produced by the
source (wind, hydro, etc.). This value is the maximum battery voltage times the
maximum source current.
For example, if a hydro source can generate up to 30 amps of current in a
nominal 48 volt system (60V maximum), the minimum diversion load size =
60V x 30A = 1,800 watts (for loads rated at 60 volts).

The diversion load must be large enough to divert ALL the current produced? Indeed that could tend to overload a 12V battery at times.

[Mike90250]

I'll propose that ANY MPPT controller with 60VDC solar input, would be fine to charge a 12V battery with. You must match the charger size to the battery & load size. PWM controllers "short" the input to the output, and a 48V battery has no inherent current limit that a PV panel has, so I would only expect the PWM controller to work for a few minutes before it fries something.
Sorry Naptown, I disagree with you here.

[dkpro1]

12 volt

Thanks - will do.

on my RV I run a 24 volt 1.2 kw system for main ac power
and a 120 watt to a 12 volt with a Sun saver duo keeps house battery and start battery
in good shape

[johngalt]

Look at the Morningstar tristar (not mppt)
You may be able to use this as a diversion controller to charge the 12V battery. Check with them on precisely how to configure this.

Thanks - will do.

[Naptown]

Look at the Morningstar tristar (not mppt)
You may be able to use this as a diversion controller to charge the 12V battery. Check with them on precisely how to configure this.

[johngalt]

How would one charge a 12 volt battery from a 48volt battery bank?

Rather than discharge my good batteries at night just to run some LED lights I thought it might be better to keep a 12 volt battery charged on the side and let that one cycle instead. All my heavy work, when needed, would be done during the day when the sun is out.. Clothes washer, dish washer, etc. If my 48volt bank is topped off and I have no work to do, and there is still sun available, how can I use that power to charge a 12volt battery to run some LED lights at night?

I know I could down convert the 48v to 12v but I was trying to figure out a way to bypass the 48v all together for this purpose.

Is this possible, stupid concept, etc.?