12v MPPT and 24v MPPT vs 24v PWM Test

full_mosey wrote:

jrnymn7 wrote:


PWM CHARGE CONTROLLERS can be used with either 12v or 24v panels, provided it's 12v panel to 12v battery, or 24v panel to 24v battery.

PWM controllers pass thru Isc.

Using the panel specs of two particular panels found on 2solar.com...

The 24v 250w panel has an Isc of 8.39a.

Two of the 12v 135w panels, adjusted down to 125w, in series, have an Isc of 7.38a.

8.39/7.38 = 1.1369... that's 113.7% Therefore, the 24v panel would deliver 13.7% more current to the pwm, and 24v battery.

With PWM, what you are saying is that the Isc : Watt ratio of the 250W panel is 6.7% and the 135W panel is 5.9%. Therefore when charging a 24V bank, then 6.7/5.9 is 1.13, or the 250W panel is 13% better.

Conclusion: when using PWM, try to get the most Isc : Watt!

Now with MPPT, you ignore all of that. You want the Vmp to be in excess of charging Volts while the keeping Voc less than the controllers Voc spec.

Conclusion: much more flexibility in choosing panels and assembling panel arrays.

HTH;
John

I hope to prove that this summer. I always got full rated panel Isc in "full sun" from my 12v panels of various wattages I had at the time using various PWM controllers I had at the time. I am hoping to see the same thing with a 24v set-up and PWM.

I stumbled across the higher Isc of the 24v 230w panel compared with 12v panels at some point lately when doing my sums, and hope to exploit that by using PWM in 24v with my 230w panel and not suffer the loss in amps I had last year using MPPT once the panel got too hot and lost power. PWM doesn't care about power. Amps is what am! :)

We'll see.

The more I get into this 24v business, the better I like it. All you need is some way to get 12v to your 12v systems in the rig and there are various ways to do that.

The key then is to have a 24v charger or converter and a 24v inverter (Or two inverters like now with big ones and little ones for the higher and lower watt jobs.)

As it is, with all 12v, I will have to isolate the bank and put it in 24v while running the rig on my spare 12v batt, charge up the bank on 24v and then around suppertime, switch it back to 12v and carry on till next morning after breakfast and swap back to isolated 24v bank again.

So how do I recharge that spare 12v battery? Overnight I plug in my 2 amp charger which is on the 12v batt to my 12v inverter which is already on anyway to run the TV/dvd etc. So that sucks AH from the bank I have to recharge next day but I can do that with the 24v routine.

Is that worth it? Probably not in terms of AH coming and going. The other way is to have some sort of 24-12 converter like oldman does and save a lot of work swapping things everyday, but not any more AH maybe.

I think the whole thing needs more figuring out to be practical, but I see a glimmer there somewhere on the horizon for this 24v business and Rving.