48v battery to 12v battery?

Brock

Ok, I am going to setup our system and was laying everything out. The place I hit a roadblock is running 12v loads. I use max 10 ah a day from a 12v battery for these small loads (AA battery chargers, cell phone chargers, cordless phone power, emergency lighting). Since I am switching to a 48v bank I am trying to think of the best way to go.

1. I could setup a dedicated small panel and charge controller and a 12v deep cycle battery. Seems expensive, but maybe less then #2?

2. I could charge the deep cycle from the 48v bank (not sure the best way to do that). I see solar converters makes a 48v to 12v 2A converters, but they are in the $150 range.

3. I could use a small battery maintainer from the 48v inverter’s output to trickle charge the deep cycle battery.

4. I could just use wall warts for all these loads. It makes me cringe to think of that...

Thoughts?

BB.

Re: 48v battery to 12v battery?

In some ways, between the losses trying to convert from 48 to 12 volts, the losses to maintain a 12 volt battery (in some scenarios), and the distribution issues of trying to get 12 volts to go a long distance to where the loads may be located.

I just keep coming back to getting a good AC inverter and running the loads at 120 VAC devices... You can send power longer distances, use lighter gauge wire, send more power, and the volt sag issues are much less (drop 2 volts out of 12--system dead... Drop 2 volts out of 120 VAC, not even a discussion point).

And the losses going from 48 VDC to 120 VAC with a small modern inverter is probably just about the same as using a DC to DC converter and dropping to 12 volts DC + losses charging the battery.

About the only question is what are the inverter standby losses and do you manually switch it's DC input or just let it idle (or load search mode--may not work with small devices like cell phone chargers)...

Today, I would only "generate/convert" to 12 volt DC if, and only if, there are loads that are only available as 12 volt DC devices.

My 0.00000002 cents worth of advice.

-Bill

For the AC loads--of course, using switch outlets to kill the phantom loads when the devices are not running (no cell phone to charge, etc.).

crewzer

Re: 48v battery to 12v battery?

Brock,

I also like the idea of a separate dedicated 48 VDC inverter to power “odd” loads. For example, the Exeltech XP250, 600, and 1100 TSW inverters are remote switchable, so it would be easy to switch one on for a couple of hours, charge things up, and then switch it off.

Another consideration might be to use run a small/medium inverter (250 W? 600 W?) full-time to power small/moderate regular and/or part-time loads throughout your home. This way, the “big” inverter(s) could be set to standby and only engage when there’s a big enough load. This configuration might reduce your tare load a bit.

Finally, the small inverter might also serve as a backup unit.

HTH,
Jim / crewzer

Brock

Re: 48v battery to 12v battery?

I don't think I explained myself correctly. My new inverter will really be acting more as grid tie but with battery backup, an XW6048 and I have a bunch of smaller 12v loads I would like to run off 12v. Almost all do come with wall warts or supply's, but in the past I had just run them from my old 12v bank. It was nice to just leave those loads on the battery and not on 120vac, and it gave me a backup to an inverter failing along with dedicated 12v emergency lighting I had around the house.

So I will have some small 12v loads, and they are all very short runs or the loads are so small I won't get any voltage drop. A cell phone takes what 100mA max? on even #14 wire that drop won't be noticeable. The biggest load would be if the grid went out and the inverter failed and the emergency lighting came on. I plan to have three 10w 12v cf's (might go with LED’s) in key places around the house. I know redundancy on redundancy, but it makes me feel better.

So that gets me back to how I charge this small 12v system, 48vdc-12vdc or 120vac to 12vdc float charger or small solar panel & charge controller.

Solar Guppy

Re: 48v battery to 12v battery?

Its not worth the effort or efficiency to have a seperate 12V system. You got the XW, so just use the wallwarts when needed to charge things ( don't leave them on 24/7 ) and for the CFL's run them off the XW again when needed.

Runnning deciated low-voltage wiring is not a win, no matter how you look at it.

niel

Re: 48v battery to 12v battery?

i think i'd go with the seperate little pv system, but that's just me. the converter will not stop operating when the battery is charged if it can charge the battery at all, wasting power and the same with the inverter being on and wasting power. a seperate system keeps waste down and gives you more control over it. you could backup that seperate system with inverter power as in standard battery charger or use a converter if you have one already for backup. you can go with or without a 12v battery too.
guppy's idea is ok if you are running the inverter all of the time anyway. it may be a thing like 6 of one and a half dozen of the other as it really doesn't matter. your choice.

Brock

Re: 48v battery to 12v battery?

Thanks, this is all helpful and I might just ditch the 12v system all together. Maybe I just needed reassurance I was over doing it. I do have most everything else on switched outlets or plug strips and they are turned on and off as needed, so I might just continue that way, I am sure my wife would prefer that

H2SO4_guy

Re: 48v battery to 12v battery?

I use 48 VDC and purchased a device off of Ebay for not too much that converts 48 VDC to 12 VDC. I think that mine will do 40 amps @ 12 VDC if you use a heat sink. I don't use that much and put a switch on it so it is not a 48 VDC phantom load. Works Great.

Skip

P.S. There are lots of things that run on 48 VDC like nice 6" muffin fans and such from the phone companies that they are not using anymore. I do a search for 48 volts and 48 VDC every so often. Have Fun!