12v from 24v Battery Bank ?

Nope. Just thought of it :) Anyway with 24v charging on a 24v battery is everything the same as 12s except half the amps? Same charging profile, SOC vs time etc?

If so it would be easy to compare results. With my 230w panel and MPPT I was getting 15.5a in the Spring and 13.5a in the Summer. With PWM I should expect 14.5a all the time based on my 130w having 8.2 Isc. (which I got)

However, the Isc of the 230w panel is 8.3 and in the summer I often saw 8.4 or so. (Isc goes up with heat) So since I get Isc with a 12v panel I should get Isc with the 24v? and is 8.3a worth 16.6a in 24v language?

I notice that the 230w and the 130w have about the same Isc, so it is not twice really. Confusing.

I would take the 16.6 worth instead of 13.5 if that is how it works.

Hells Bells BFL13,

I thought that was what you were trying to accomplish from post #1. I.E. get a pwm to harvest well from a high voltage panel.

BFL13 wrote:
Now I am wondering if my summer problem with MPPT and panel heating reducing the amps I get compared with PWM could be got around by charging the batts with PWM in 24v. Not sure how I could check that out as a field test this summer. Have to work on that.

The 12/24 PWM controllers I have used do not list their Voc limits like the MPPT controllers do, so that remains a gamble. I did try the $15 RJ Special I had with the 230w panel to see if it would just run it to its Isc. I didn't mind risking the $15. :)

The controller's little red lights (several of them) all flashed rapidly and no amps got to the battery. I figured it was fried, but then tried it on a 130w panel and it worked properly.

I have not tried that with the Solar30 controller so it remains a mystery if it would run the 230w or not on 12v batts, and fry or not.

I have tried the 230w in panel- direct as a test, and it did that ok.

Now I am wondering if my summer problem with MPPT and panel heating reducing the amps I get compared with PWM could be got around by charging the batts with PWM in 24v. Not sure how I could check that out as a field test this summer. Have to work on that.

There should be no problem using the 24 volt panel with a PWM controller on a 12 volt battery bank if the controller can handle the open circuit voltage of about 38 volts. The panel voltage will be pulled down to equal the battery voltage. This will cut your watts in half. Your 230 watt panel will produce only 115 watts. Your current will not exceed the short circuit amperage rating of the panel.

One possibility that this might not work is if the controller detects the large difference between voltage in and voltage out and shuts down.

Another option would be to eliminate the controller and hook the panel directly to your battery bank. You would have to monitor your battery voltage closely to prevent over-charging.

You guys are gona make me dig my old Heathkit out

Heathkit and Eico! omg

Electricity can be fun too. Twist the secondary windings of a power transformer together, then plug the primary into the wall. Things get hot, real fast.

Also, some electrolytic capacitors act just like firecrackers when 120vac is applied.

I don't think any of that was included in the Heathkit instruction manual.

Mex, I don't want to take Grade 8 "Electricity" again as part of "Industrial Arts" in 1955. It would be as lost on me now as it was then.

I vaguely recall mention of Kierchoff's Law (however spelt) while the instructor passed around those big Ouiji board/Chinese Checker monster things with wires all over the place. Forget what they those boards were called, but I know they were important. (I was such a waste of classroom space. Oh well.) Edit: Wheatstone Bridge ? Incomprehensible! :(

It didn't help that the Electricity instructor would sometimes burst into tears and rush out of the classroom. Then another teacher would come in and say, "Don't mind Mr X, he saw some terrible things during the war. He will be back shortly." Which he was. ( A little touch of reality about going to war like that sort of put a damper on all us Grade 8 kids who wanted to be John Wayne at least)

Electricity was ok, but not as much fun as "Metal Work" where we got to play with giant soldering guns that you stuck in these blocks of paste for maximum smoke. The kid that made the most smoke won! :)

Google Kierchoff's Law the amperage throughout a simple series circuit remains EQUAL from begging to end. Wanna see a 12-battery try to get to 17-volts?

THIRD battery fed by pair of independently wired DC to DC high converters. They are cheap enough and a pair will give you 30-amps potential set to whatever voltage you team the pots to. This is a permanent DC/DC charger. The 3rd battery allows high surge draws.

If you have to spend $100 or so on a DC/DC converter, you might as well spend that going to MPPT from PWM and get the buck converter that comes with the MPPT. (for a long term set-up using 24v)

I was just looking at what you could do with the tools at hand if you were caught with a suddenly dead MPPT controller and have a 24v panel and only a 12/24 PWM controller lying around as a spare. Also when your battery bank is able to become 24v with a wiring change.

Another reason to have two 12v panels instead of one big 24. You can still be 24 but could go 12. However the price of 12s is becoming a problem. :(