Author Topic: 48 volt to 12 volt controller (Read 3946 times)

velacreations · « **on:** January 24, 2006, 02:19:06 PM »

What sort of controller hould I use to go from a 48 volt solar array to charge a 12 volt battery bank. I know I can just hook them up straight, but I want to take advantage of the extra amps avaiable in the solar panels. They are currently running a solar pump at 48 volts with 4 panels, but I only run it 30 minutes a day, so the rest of the day, I would like to be charging batteries.

Does anyone have any ideas?

johnlm · « **Reply #1 on:** January 24, 2006, 07:27:09 AM »

I would use a DC to DC convertor. 48V in 12V out modules are pretty common. You don't say what your panels are capable of wattage wise so Im ot sure what power rating of DC-DC module you would need.

John

Nando · « **Reply #2 on:** January 24, 2006, 07:30:02 AM »

You did not say the power available form the panel.

To charge the 12 volts from 48 volts, you may use a Xantrex MX60 charger controller, though a bit expensive.

This controller does have a good battery charging profile.

Another way is to use a Voltage converter, all depends on the watts available from the panels.

Nando

crashk6 · « **Reply #3 on:** January 24, 2006, 11:03:54 AM »

Nando,

Don't you mean an Outback MX60? It is indeed capable of buck/boost type convertions. And I agree they are pricey, but if you can afford it they are about the best for solar.

Xantrex makes the C Series controllers, they make a 60 ampere unit, the C60, but it is not capable of voltage conversion... at least not to my knowledge. I have however used the C series (a C40) in conjunction with buck regulators to achieve lower line losses from distant charging sources. I am going to be doing it again charge a 24 volt battery bank. The solar array ran at 60 volts and the hydro ran between 90-120 volts give or take depending on flow. The C40 was used in diversion mode.

--

crashK6

drdongle · « **Reply #4 on:** January 24, 2006, 03:06:53 PM »

http//:www.astrodyne.com has off the shelf DC to DC converters, their SVA15SC48 is a 38-63 V input to 15 V, 3.4 A output efficiency is 82% and cost is $115.00

The ASD50-48S15 is $68.00

danielbergamini · « **Reply #5 on:** January 24, 2006, 03:24:57 PM »

I also highly recommend the OutBack MX-60, but at near $500 it is a pricey option. I used it in a similar configuration that you needed, I'm running my panels at 48V and batteries at 24V. I also found another cheaper option that based on what I've read will allow higher panel voltage then batteries, but I have not confirmed it will actually fit your needs. It's the Morning Star TriStar series. $200 for 60 AMPS, $160 for 45 AMPS. Might be worth checking out.

velacreations · « **Reply #6 on:** January 24, 2006, 07:11:55 PM »

Well,

Each panel is about 7 amps, so right now, they are generating 48 volt at about 7 amps, but I would like to charge the batteries at 12 volt, say 28 amps, so not a whole bunch of power. 400 watts or less.

I would like to stay around $200, so maybe I'll see about Morning Star.

Nando · « **Reply #7 on:** January 24, 2006, 08:41:55 PM »

Heck !!! YES, I meant OUTBACK, I put my four feet in my mouth !!.

Nando

Clifford · « **Reply #8 on:** January 24, 2006, 09:34:05 PM »

Other options...

Why not wire the panels to 12V, then get a 12-48V converter to run the pump? And, you wouldn't even need to have sun to run your pumps.

You could, of course, wire the batts to 48V... Too bad there isn't an auto sensing switch which could pick out the battery with the highest charge to pull 12V out of.

I've been pondering the sensibility of point of use 48/12V converters... thus, if you were running lights, for example, they wouldn't run the converter unless they were actually turned on. Of course, if you are running CFL's... they have a "converter" built in, just need to get the right ones.

velacreations · « **Reply #9 on:** January 25, 2006, 08:01:07 AM »

Well,

The pump is more efficient at 48 volts than 12, and so the panels have been wired that way. I hadn't really though about wiring for 12 and then jumping up. I assume going 48 to 12 is slightly more efficient than going 12 to 48, but maybe I am wrong.

Thanks for all the suggestions.

crashk6 · « **Reply #10 on:** January 25, 2006, 10:11:42 AM »

Sometimes in life we tend to overcomplicate things, so I have another few suggestions that are going to go in mostly the other direction compaired to my last post.

As I was reading in your later posts, the load you primarily wish to power is the pump, correct? The pump is most efficient at 48 volts, and so are the panels to run it. It is currently running solar direct, but now you would like to store that extra power for some as yet unstated pourpose... perhaps running the pump at night?

Well why not just get an inexpensive, strait 48 volt charge controller and setup your bank of batteries at the pump station at.... 48 volts!

Then if you have any additional load you'd like to run you could use a small (cheaper) dc-dc converter to run it, now if it's just that you want to run some lighting from the battery as your additional load you could forget the dc-dc converter and just get CF's ballasted at 48 volts.

It would be so much simpler.

On the other hand if you have some specific and unchangeable reason to be charging a 12 volt battery, maybe you should check out battery backed pump controllers, some can charge lower voltage batteries while leaving the rest of the system (pump and panels) running at the higher voltage. Although others are really just charge controllers that do just what my above suggestion entailed (eg all 48 volt) but tend to offer MPPT on top of the standard PWM charging profile, which will squeeze out some extra power for you.

Check out www.solarconverters.com

They make all sorts of things to solve little problems like this, and might have just the thing for you. If you don't see what you want give them a call for a consult and price quote.

I've had good luck with their stuff, not dirt cheep but I've felt like you get your moneys worth. I like to install something once and not worry about it again, so poor quality anything finds it's way to the bin pretty quick around here.

--

crashK6

wpowokal · « **Reply #11 on:** January 25, 2006, 04:00:01 PM »

I may be totally wrong but could not the 4 panels be wired for 48 or 12v with a few blocking diodes.

I know there will be losses but there also will be with converters.

I have not drawn this out but thought I would throw it in anyway.

allan down under

drdongle · « **Reply #12 on:** January 25, 2006, 06:00:22 PM »

You can't have both at the same time.

Drives · « **Reply #13 on:** January 25, 2006, 07:20:39 PM »

I wish I had a long time for this explanation, but I don't, so here goes.

If your pump motor is PM (two wires), your pump is a centrifugal type, you are pumping to fill a tank, not for pressure, and your head is low....then your pump efficiency will increase if you run the pump at 12vdc vs. 48vdc.

To prove it, take a current reading on your pump draw when you are operating at 48vdc vs. 12vdc. A nice added benefit is you will get a very long life from your motor and pump. Yes, if your DC pump is rated at say 120vdc/1750RPM and you run it at 12vdc/175RPM, you will not harm it. Even though you run it at a reduced speed, and have reduced cooling effect from the fan built into the motor, your load has decreased dramatically, thus no heating effect, just slow, efficient operation, that will last a long time. You may find brushes are used up quicker, due to light loading, but at 2 hours run time a day, I wouldn't worry about checking them every 3 years or so.

If you have a positive displacement pump, or are pumping a pressure tank, or have a high head to pump, this will not work.

Look up the Affinity Laws of centrifugal pumps and fans. It roughly states if you reduce the speed of a pump or fan by 10% your flow is reduced by 10% but your load (amps) decreases by 27%. Meaning flow is proportional to speed, but load (power) is proportional to the speed cubed. (Sound familar?

Wind mills in reverse) Remember speed of a PM DC motor is proportional to voltage applied to the armature.

Your will need to run your pump for 4 times longer (roughly 2 hours) to pump the same amount, but you will be able to configure your batts and solar cells for 12vdc.

All small pumps can handle this usually. Big pumps have special cooling and lubrication issues with running below 25% speed.

This technique has been done in industry, waste water/water treatment, HVAC, etc for years. To slow the speed of an AC motor we use variable frequency drives.

Drives · « **Reply #14 on:** January 25, 2006, 07:25:13 PM »

Wher I said load (amps) decreases by 27%, I was wrong...load is equal to power which is equal to watts, Thus volts times amps = watts. Your amps will go down, but it is your watts that decrease by 27%.

Like I said not enough time, to do the explantion justice.

ghurd · « **Reply #15 on:** January 26, 2006, 06:32:57 AM »

How about a switch? One way 48V for the pump, the other 12V to the batteries.

A 6PDT-CO $witch should do it, maybe 5 or 7 poles?

I figured out 4 panels for 3 voltages (ie. 12/24/48) using a 4PDT and a 2PDT. Same idea should work. Would take a lot of wire unless the switch was near the PVs.

G-

velacreations · « **Reply #16 on:** January 26, 2006, 07:50:55 AM »

Actually, I disagree with the pump being more efficient at 12 volts. First, there is line loss. Second, this is a grunfos pump that is designed to run on 30-240 volts DC, so 12 volt won't cut it. With a higher voltage, the tank fills up in 30 minutes.

I personally think an awesome MPPT controller would do the trick. I have to have to batteries at 12 volt for my camper, and although I could change the battery bank to 48 volts and then convert for appliances, that seems like more money for less. With the MPPT, I should be able to charge the 12 volt bank from the 48 volt panels set without the need for extra components.

Now, it is true, we could wire up for 12 volt, then boost for 48, but it seems like there is more loss in boosting than dropping. Maybe I am wrong, but that's what I see.

Anyway, I think the controller will handle it, and I found a decent one for $200, so with that one component, the whole system can work fine. The pump is only on for 1/2 an hour anyway, the rest of the day, I should be charging batteries.

Drives · « **Reply #17 on:** January 26, 2006, 10:29:32 AM »

Vela:

You may be right about the Grundfos pump and motor not working properly at 12vdc, you did not give the model number for me to investigate.

I don't have a large amount of experience with very small pumps, but anything from 10HP to 2,000HP (1.5 Megawatts), I really shine. I know the principles still apply to all centrifugal pumps.

To prove the point, put 48vdc on the pump and take a current reading, then put 12vdc on the pump and take a reading...would be interesting to see the difference.

Clifford · « **Reply #18 on:** January 26, 2006, 09:41:10 PM »

Hmmmm...

I'm wondering how you will wire it all up.

Too bad I never studied elementary electronics

Anyway, say your pump takes 50% of the power from the panels...

If just attach your pump before the MPPT and then the MPPT to the batteries.

You may find that the MPPT steals too much current and your pump won't work.

If you shut off the MPPT while running the pump, then you will be wasting power, and probably have a less efficient system than using a 12V to 48V converter.

I presume the answer is a well placed resistor between the pump and the MPPT. Preferably you would take the resistor out of the circuit when not running the pump.

Somebody else will have to suggest the size of the resistor though.

Another thing to keep in mind... Most MPPT systems loose efficiency if you are less than 100 Watts Solar input. It may not be a big deal, but your efficiency will probably be similar to coupling a 48 to 12V converter to a "standard" charge controller (except, of course, that the MPPT is an all-in-one unit).

ghurd · « **Reply #19 on:** January 27, 2006, 09:15:15 AM »

Over simple? How about 12V to an inverter, to a 48V regulated DC supply. 30 minutes a day isn't that much.

G-

scottsAI · « **Reply #20 on:** January 28, 2006, 12:06:16 AM »

By gorge I think ghurd has it.

Efficiency is important for what it does longest.

30 min a day is not the important point to be considering.

You have 7 amps * 48 = 336 watts.

48/3 = 16v

Looks like 3 - 100w plus panels.

Not using the panels for the rest of the day is... inefficient.

You are waisting 336 * 5 = >1500 watt hours a day.

If you can rewire to 12v system and get a 400 w 12v charge controller.

Add a big battery. Something > 1500whr Like two golf cart batteries (6v ea at 225ahr)

To run the pump a 400-500w inverter for $30 + 120v to 48v power supply.

Ebay item 7214178280 is a 48v battery charger 8amps $60.

Now you have almost a whole day of sunshine to power everything else.

Have fun,

Scott.

ghurd · « **Reply #21 on:** January 28, 2006, 08:54:33 AM »

I wonder if the 48V even needs to be regulated for a pump.

Maybe just a big (cheap) rectified transformer?

G-

scottsAI · « **Reply #22 on:** January 28, 2006, 01:08:27 PM »

I think your right.

I was looking for 7 amp 48 volt anything.

Charger was the first thing I could find.

Wanted 12 to 48v converter, cost much more than your suggestion.

If the inverter is larger, then maybe can use with other loads.

Or have a dedicated inverter for just this pump, another inverter for other loads.

Only need to turn on the inverter needed.

Have fun,

Scott.

scottsAI · « **Reply #23 on:** January 28, 2006, 11:55:45 PM »

I just realized the pump runs on 30 to 230vdc.

Use the inverter, rectify the AC to DC, add capacitor then to pump.

Forget the charger or other means to get 48v!! Not needed.

Have fun,

Scott.

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Author Topic: 48 volt to 12 volt controller (Read 3946 times)