solar controller for 24v to 12v sub system

[NEWFISHER]

On a 24v pinz, could you pull current from the 24v battery bank through a mppt 30a solar controller and charge a 12v battery? From the 12v battery, run anything 12v off a sub panel including a winch?
http://vi.raptor.ebaydesc.com/ws/eBayIS ... 8858911441

Or a 60amp version
https://www.google.com/search?q=mppt+so ... oATil5SQBQ

[Jimm391730]

could you pull current from the 24v battery bank through a mppt 30a solar controller and charge a 12v battery?

Probably not. Although it sounds like a good idea, most charge controllers (especially PWM controllers) "short out" the panels as the battery gets close to full charge to limit the energy. This is because it is simpler in circuitry to short out the panels (they have a maximum output current), as the panel short circuit current is known and limited by the panel itself.

If the controller is powered by a battery the possible current is almost unlimited, and the MPPT controller will try to maximize power from the battery source (meaning that the current will attempt to go VERY high). The better the controller, the more likely it is to limit this current, but this is not how the controller was designed to operate. Then when the 12V battery is fully charged it will depend on how the controller is designed as to what it does to slow down or stop the charging energy.

The first link shows "PWM" on the manual, so it is VERY likely to short the panel as the battery gets up to full charge; I'm not as certain about the other, more expensive MPPT controller. If you only consider charging the battery (not ending the charging of the battery) then an MPPT controller might work, but once the battery becomes fully charged then the operation changes and the magic smoke may be released!

[rmel]

The only converter I have found on the market that is designed as a dual function
MPPT/Charger is from the land of Oz -- go figure
https://www.redarc.com.au/products/prod ... arger-40a/

They ain't cheap, I have one, had to import it myself, and that was when the AUS=USD in
exchange rate. More affordable now at 1.4 to 1.0 exchange rate.

The REDARC is intelligent in the sense that it knows what the source is Solar or Battery.
When connected to a 24V battery system it knows not to enable the 12V output charging
unless it detects the Alternators tell-tail full bridge ripple -- you won't crater your 24V
before starting

As Jim points out a plain vanilla MPPT won't work properly.

ron

[NEWFISHER]

The only converter I have found on the market that is designed as a dual function
MPPT/Charger is from the land of Oz -- go figure
https://www.redarc.com.au/products/prod ... arger-40a/

They ain't cheap, I have one, had to import it myself, and that was when the AUS=USD in
exchange rate. More affordable now at 1.4 to 1.0 exchange rate.

The REDARC is intelligent in the sense that it knows what the source is Solar or Battery.
When connected to a 24V battery system it knows not to enable the 12V output charging
unless it detects the Alternators tell-tail full bridge ripple -- you won't crater your 24V
before starting

As Jim points out a plain vanilla MPPT won't work properly.

ron

Good info. Jim," letting out the magic smoke" makes me spray my keyboard with soda.

I have " searched" for the best way or most used way of adding a 12v system to a Pinz, but have come up with:

1) Get a 24v winch and run a 24-12v converter for the small stuff. I will be adding a Webasto/Erbspacher and a fridge also.
2) Fab a mount and run a second mini 12v alternator but be careful of voodoo magic grounding etc.

Anything else that seems better?

[rmel]

There are beefy 24V to 12V converters, 40A or higher.

In rough terms the drain on the 24V side is ~1/2 that or a tad higher than 20A.
I'd go that route over a second alternator. Works great for any electronic/electrical
load, and most converters have a constant ~13V output. Won't work for a significant
inductive load such as a Winch -- way too much current draw for that -- thus the
need for a 12V Battery for a 12V winch.

The other approach is an equalizer, also significant output at 40A. The drawback with
a battery equalizer is that it really looks like a virtual 12V battery. That is, as you take
charge out of the pair of batteries the 12V will drop, if you have voltage sensitive gear
(HAM radios for instance or PC's) it may not play nice unless your alternator is running.
With some gear they say it's 12V when the fine print says 13.6V

Lots of ways to go here, all depends upon what your end game is.

[rmel]

Oh! One positive feature I forgot to mention about an Equalizer is that such a setup can provide large instantaneous current draw (I just
would not recommend using it that way for very HEAVY loads such as a winch). The reason why this setup can provide higher than the
rated output of the equalizer is because the 12V load is directly connected to the bottom battery, as is the output of the Equalizer too.
The equalizer just makes sure that both batteries discharge equally. The IMHO one of the best is from http://www.vanner.com/battery-equalizers/,
the boating guys like them for their robustness.

[NEWFISHER]

Part of my issue is I have several 12v warn winches laying around. I only need a 12v cell charger and 2 ports for fridge and webasto. Lookingncor a simple solution without buying another winch ;(

[krick3tt]

Just have the motor rewound, I have heard that can be done. Got to be cheaper than a new winch although I have no experience with this.

[rmel]

Well then, this should work http://www.vanner.com/manuals/70-60.pdf,
I'd go for the 60A model -- plenty of capacity.

The tech note claims the unit will operate just fine if the bottom battery sees a surge
of current beyond the max. output.

If you have gelcell batteries, lay them on their side and you should be able to squeeze
the converter into the battery box. Run a good hefty wire off the middle terminal with a 400A
fuse for your 12V winch. Run a second lighter duty wire (fused) for your creature comforts.
If it were me I'd put one of your 12V winches up on eBay and get a 24V with a synthetic
rope -- safer and lighter.

ron

[waterdog]

i have this set up.. a solar panel charges a 12V marine battery, when the truck is running the alternator re-charge this battery, turn off the truck, solar panel kicks in.....but is for a fridge, a radio, water pump,air compressor,led lights... not too much amps..i wish a could run a 12v winch....