48 volt bank to power 12v loads?

Brock

I know there are a couple of ways to do this but I have a 48 volt battery bank. Right now I am using a 120vac switching battery charger (powered from the inverter) to keep a 12v battery topped off that is powering a bunch of 12v loads I have.

I was thinking of switching to a solar converter or something similar, maybe avoiding the 12v battery all together? Or maybe leaving it there to even out the loads? Right now I have about a constant 1.5 amp draw off that battery (routers & switch & modems), but if I load up the NiMH battery chargers and flip on a 12vdc CFL it is up to about a 5 amp load.

Thoughts

Cariboocoot

Re: 48 volt bank to power 12v loads?

This issue has come up before I'm certain.
I also think the way you're handling it now is probably as good as any, if not the best. DC-DC power supplies have some drawbacks, cost being one of them.
There's some loss of efficiency in your DC-AC-DC conversion, but if it's working for you why change it?
Maybe you want to add a panel on the roof and have an entirely separate 12V solar set-up?

BB.

Re: 48 volt bank to power 12v loads?

Search Google for: "dc to dc power converter 48/12 vdc"

And you should find quite a few... One of the best (at least low power paper specs.) seems to be this 15 amp output unit (no price listed--may be scary).

What I like about it is the 65 volt maximum input voltage (and 35 volt low)... Most of the others are 60 volts peak (may be an issue or not for your system)--and others that are only 50 volt peak (not acceptable).

The converters are probably around 85% efficient. Probably beats a good Inverter/12 volt converter combination.

Normally, wholesale pricing should be in the $0.50 per watt; Retail would be 2-4x the cost (for any standard function/quantity production converter).

Vicor is a very good/high quality mfg. of "power bricks/converters"... They where always to expensive for my applications--but perhaps you can track down one for your use (telecom spares, scrap, over-runs, etc.). When I lasted looked at them a couple decades ago--they did not stock product--but built to order (automated line).

Digikey.com has a nice 100W DC to DC converter with the following specs for $180 (even has remote sense for output votlage--very nice option--I wish the solar charge controllers had this too):

Voltage - Input 18 ~ 75VDC
Output 12 VDC @ 8.3A

I wonder if you could take a, for example, a Morning Star 15 amp MPPT charge controller--connect it to the 48 volt bank and throw a storage battery (AGM would be nice) on the output. Seems like it should work OK at a reasonable price (~$260 + batter cost).

-Bill

mike95490

Re: 48 volt bank to power 12v loads?

See this thread also,
http://forum.solar-electric.com/showthread.php?t=5257

That new Vicor VHK100W-Q48-S12 part looks nice, all in one package

Brock

Re: 48 volt bank to power 12v loads?

coot, just after I wrote this up I thought, hummm, what size panel and controller would keep me running 24x7. And for the cost of some of the DC-DC converters you might as well go to a solar panel and cheap controller.

I was wondering what the cheapest solar controller that can accept 60vdc in to 12vdc out? I know I could get the MX-60 to do this, but that would be a really expensive way, which got me to wondering if anyone made an inexpensive charge controller in the 5 to 10 amp range.

Mostly I had been looking at the "solar converter" line, but they seem so expensive...

BB.

Re: 48 volt bank to power 12v loads?

Brock,

What is the intent with the "60 volt" panels and the 12 volt load?

Are you thinking of paralleling a charge controller onto your existing array and running the 12 volt battery off of that?

I don't think you should try paralleling MPPT controllers, and a PWM, if it did work, would just collapse the 60 volts down to 12 volts + change.

Or, are you planning on building a separate "60 volt" array so you can have long cable runs from the array to the battery "shed"?

The smallest MPPT controller with the highest input voltage seems to be the Morning Star MPPT 15 amp unit with 72v Voc max input (as I remember).

-Bill

PS: If you where going to do the whole second 12 volt battery thing--I would really consider the MorningStar MPPT running on your 48 volt battery bank directly (properly fused, of course) charging the 12 volt battery...

I like the idea of one array charging all of your battery banks--allows you to put the power where needed--instead of islands of power (some too much, others too little).

Perhaps Solar Guppy would be the one to answer if this is a safe idea or not (I am sure that MorningStar would answer no!).

-Bill

icarus

Re: 48 volt bank to power 12v loads?

Brock,

My thoughts exactly. A simple Pv, Charge controller and battery just for your 12vdc loads would probably in the net/net be cheapest and most efficient.

Tony

Brock

Re: 48 volt bank to power 12v loads?

Bill I was thinking of connecting the controller to the existing 48vdc battery bank on the solar panels side and the 12v battery on the 12v side side. The advantage as you said there wouldn't be any power wasted, whatever any panels made would feed the 48v bank and then the controller would just feed power as needed to the 12v battery.

I just can't help but think there has to be an easier way. Maybe even the Solar Converter line, 48 vdc to 12 vdc would be the way to go. I only need like 2.5 amps at 12v max, usually like 800 mA and the battery could buffer any short-term larger load.

But then again what Tony said, just a stand alone small system or "island" might be more straight forward...

Brock

Re: 48 volt bank to power 12v loads?

These are the two items I am looking at, but they seem to be custom made. It looks like Wind & Sun carries their line though...

This one looks like a fixed ratio
http://www.solarconverters.com/equal3.htm
that would work and I could even ditch the 12v battery with this one.

Otherwise a small mppt controller
http://www.solarconverters.com/sp48_5.htm

icarus

Re: 48 volt bank to power 12v loads?

Brock,

I was running the numbers for an added Pv and controller set up and I think you have hit upon the best solution. I have the same type converter to run my pump on 24vdc. While adding a separate Pv system would work, it would be more expensive net/net.

Tony

PS I have a source for them if NWAS doesn't sell them,, ~$200 us for 48-12vdc unit.

Cariboocoot

Re: 48 volt bank to power 12v loads?

Budget may be the deciding factor here: which of the several different ways of doing this will cost you the least?

That second link is a CC for a 48 V battery, btw. You'd need the 12 V equivalent, right?

Nice to know there's options.:D

BB.

Re: 48 volt bank to power 12v loads?

Go back and define the loads--steady state, on 24 hours per day, high surge, able to run independent of "main" panels for a time, issue with battery life/replacement costs, electrical noise, etc.

The "Solar Converter Inc." products look interesting too... But they have proportional and regulated output models... And models that could charge a battery.

Lots of choices, but you will narrow down the list by defining your load requirements more closely.

I think you need to look at standby losses closely -- especially if running 24x7. Many devices specify efficiency at some optimum point--and when you operate outside that point, your efficiency can drop (i.e., 5% efficiency at full current of 10 amps, may mean a 0.5 amp minimum internal loss (0.5a*12=6 watt loss with low loads).

-Bill

Brock

Re: 48 volt bank to power 12v loads?

Bill I think you nailed it. What I have now does work, but I don't really need the battery in there. It just ended up being the "capacitor" for the battery charger to work. So I am adding unnecessary loss by having it in the loop. Still when running the charger (has a fan that runs no matter what) pulls about 30w, ignoring initial inverter loss and the 6 separate power cubes pull about 50w, again ignoring initial inverter loss. So I am a bit ahead doing it this way. But the actual load from the battery only measures 1.45 amps at 13vdc or 18w.

I think I need max of 4 or 5 amps and would prefer to avoid a battery all together, which again leads me back towards the solar converter. Coot thanks for pointing out that second one was a 48v cc, I didn't look closely enough at it.

So I think I will see how much the solar converter cost or if in the end I just leave it alone the way it is.

Brock

Re: 48 volt bank to power 12v loads?

Jumping back to this, killed my second 12v battery, both were old car batteries close to death anyway. My thought now is going with a converter like the solar converter line (48/12 at 10 amp) are going to be in the $215 range, for that much money I was thinking of just going with the Morning Star Sunsaver MPPT 15

http://store.solar-electric.com/mosumpsochco.html

Would the recommendation be to hook that in parallel with my existing ~65v array and obviously connect the Sunsaver to a 12v battery or connect the Sun Saver input side directly to the 48v battery bank? I like the idea of connecting it to the 48v battery bank so the smaller 12v battery would not actually cycle, but just draw power from the larger bank as needed.

This also gives me an option of using "some" of my array with a 12v battery and inverter in case my MX-60 or XW6048 failed.

BB.

Re: 48 volt bank to power 12v loads?

If your main array is already running on a MPPT type controller, then you should not connect another MPPT controller in parallel to the same solar array.

Next, the Sun Saver has a maximum of 75 volts on the solar input (as I recall). If you have a Vmp=65 volts array--Voc would probably be too high (cold weather, no load, etc.).

I would check what the "standby current" of the MorningStar 15 amp MPPT controller with the battery bank on standby--it may end up the same or less vs just using a 48/12 converter anyway.

If you decide to place the MorningStar MPPT directly on the 48 volt battery--definitely add some sort of fuse/breaker to protect the controller and wiring:

• 15 volts * 15 amps * 1/42 volts min * 1.25 safety factor = 7 amp or next size up (8-10 amp fuse and wiring). I assume the MorningStar is rated for at least 15 amp continuous when used with solar panels--So 12 awg wire and 15a*1.25=20a maximum fusing for "safe" operation

One other issue to watch for--some MPPT controllers place a shunt resistor in negative side of the solar panel input--so you cannot have a common ground between Vin and Vout for the charge controller (Xantrex XW MPPT controller is the one I recall as having this negative shunt resistor). So for those types of controllers, you will not be able run a common negative ground between the 48 volt and 12 volt battery banks (one of the banks will have to be floating with respect to ground--probably the 12 volt slave bank).

I don't remember the MorningStar as having a negative sense resistor. From the PDF manual it appears that any grounding combination is OK:

NOTE: The SS-MPPT is a negative ground controller. Any combination of negative connections can be earth grounded as required. Grounding is recommended, but not required for correct operation.

One recommendation on grounding--Be careful that you home run the 48 volt grounding separate from 12 volt loads/grounding... You don't want (the probably large) 48 volt return currents going through the MorningStar MPPT solar/battery negative connections.

-Bill

PS: I have never done anything like this type of connection--But Solar Guppy has suggested this configuration before (if I recall correctly)--so hopefully he can confirm/correct my assumptions.

Brock

Re: 48 volt bank to power 12v loads?

Sounds good. I think hooking the Moringstar up to the battery bank sounds like the way to go. I will leave the 12v battery floating and not common ground it since the loads are 12v anyway. Again the cost of a 10 amp converter is $10 less than the Morningstar and the Morningstar will "take care" of the battery rather than a straight conversion from what ever the higher bank was at in the converters case.

Brock

Re: 48 volt bank to power 12v loads?

I got the Morningstar SunSaver MPPT 15 charge controller from Wind & Sun with the usual great pricing and really quick service

I have it hooked up and everything seems to be working great. I have three questions.

I wired the loads through the "load" on the controller, since I am only drawing about 2 amps I should be fine. My question is does the controller somehow keep the voltage lower when it does its auto EQ once a month or should I remove the electronics when this happens or disable the EQ charge? I did remove that flooded jumper.

Secondly, should I just leave it connected 24x7 to the 48v bank? The controller is just sitting there in float mode. I am assuming it stay in float unless it hits its monthly eq? Or should I disconnect it weekly from the main battery bank for some reason? It just seems the controller will never see "night" from the solar input, I don't know if it matters or not?

And lastly with this setup the 12v battery will never really see a load, I am assuming the SunSaver will just supply all the power to the loads from the 48v bank. What would it do if I removed the 12v battery or used 10 or 11 NiMH AA cells in its place, probably not work? I am just thinking of reducing the "float" load of maintaining that 80 amp battery.