Looking for feedback

System

Am new to the forum, and see alot of good advice so I thought I'd throw my puzzle out there..
I have a 2- 130w panel system going into a 35a diversion controller that goes into either the battery bank ( 3- 12v batteries), or the resistive dump load.

Ive ripped the system apart, and tried every possible idea or replacement. No matter what, I can only get 10a of charge current into the batterys.
** During dump load it gives 14a. **
Tried a different controller, even took the controller out and tried the panels to battery direct, but no difference...
Also tried 1 battery - charged at 10a
also tried 2 batteries- charged at 10a
" " 3 batteries- charged at 10a
tried taxing the system with 30a load while charging, no change

Why are the batterys limiting the charge current to 10a when 14a is available???

BB.

Re: Looking for feedback

Can you tell us more about your charge controller setup?

Generally a charge controller is setup for in line charger OR as a diversion mode controller. It sounds like your controller is setup for both modes at the same time.

-Bill

System2

Re: Looking for feedback

BB. wrote: »

Can you tell us more about your charge controller setup?

Generally a charge controller is setup for in line charger OR as a diversion mode controller. It sounds like your controller is setup for both modes at the same time.

-Bill

Im not really following you.
controller is a GF-1235 controller, and very simplistic.
http://www.green-first.com/controllers.shtml

personally Im not the happiest with the controller and plan on changing but it was a great starting point.
At one point during troubleshooting, i took the controller completely out and wired the panels direct to the batterys.. And still only got the 10a charge to batterys.
then disconnected batterys and wired up a resistive load in their place which got 14a.

mike95490

Re: Looking for feedback

if th batteries are full, they won't take much of a charge. Throw a couple loads on them for a few minutes, then hook up the PV.

BB.

Re: Looking for feedback

Interesting controller...

Do you have an accurate voltage on the battery bank before charging and during the 10 amp charge?

Also, what are the brand/model or Vmp/Imp of the solar panels you are using?

Assuming they are around 17.5 volts Vmp, and a PWM charge controller:

• (130+130 watts) * 1/17.5 volts * 0.77 derating = 10.12 amps

All in all, that seems to be pretty close to what I would expect all things being equal (average sunny days, not too hot, average PWM controller charging a battery bank that is below 90-80% state of charge at ~14.4 volts or so...

Solar panels tend to be rated by marketing numbers which are, for the most part, only apply to very cool / clear days... (standard test conditions are with the panel at 70 or 77F and 1,000 watts/sq.meter for a few seconds--Panels tend to run much hotter--can be as much as ~65F hotter than ambient--which depresses their Vmp output voltage).

-Bill

System2

Re: Looking for feedback

mike90045 wrote: »

if th batteries are full, they won't take much of a charge. Throw a couple loads on them for a few minutes, then hook up the PV.

thanks Mike & BB,

I did NOT dump the batterys down before my troubleshooting/experimenting of trying to charge them back up..
But when i put a 30a load on them while charging from the panels, i was still only getting 10a charge current. A 30a load should draw any remainder power available from the panels.
Actually come to think of it... i did notice a small solar charging current change while varying the load up to 30a.. first i thought it was clouds passing.. but it did vary from 9.1a (no load on batts) charging up to the 10a (30a load on batts). thought that was odd, so I double checked it a couple times to make sure..

Also it baffles me why a single battery would take 10a, 2 batterys took 10a, and 3 batterys took 10a..

heading out of town now, but am going to stop in on the panels on the way thru. Hopefully will have good news when i come back.

System2

Re: Looking for feedback

BB. wrote: »

Interesting controller...

Do you have an accurate voltage on the battery bank before charging and during the 10 amp charge?

Also, what are the brand/model or Vmp/Imp of the solar panels you are using?

Assuming they are around 17.5 volts Vmp, and a PWM charge controller:

• (130+130 watts) * 1/17.5 volts * 0.77 derating = 10.12 amps

All in all, that seems to be pretty close to what I would expect all things being equal (average sunny days, not too hot, average PWM controller charging a battery bank that is below 90-80% state of charge at ~14.4 volts or so...

Solar panels tend to be rated by marketing numbers which are, for the most part, only apply to very cool / clear days... (standard test conditions are with the panel at 70 or 77F and 1,000 watts/sq.meter for a few seconds--Panels tend to run much hotter--can be as much as ~65F hotter than ambient--which depresses their Vmp output voltage).

-Bill

Wow. i never would have thought that 10.12 would be right, but your math works.

One of the panels is a kyrocera, and the other a new off-brand off e-bay. Dont recall numbers off the top of my head, but 17.1v to 17.5v sounds right. Max current - 7a to 7.1a each

Yes, have a voltmeter hardwired in. Battery voltage varied abit while charging. Also ran 3 seperate ammeters during testing, all were close enough within a hundredth.

RE: operating during cool days

I understand Jan & Feb being more optimal conditions,
this set-up is on my fish house (cabin). which i live in on the ice during Jan & Feb. Last winter, i could swear i was getting 7a charging from 1 panel.. Now just this summer, i installed the second panel.. this is why i was also expecting 14a. (7a x 2)
even so, this doesnt explain why when i disconnected everything. and went straight from the panels to the dump load, i was getting approx 14a.

gotta run, going to the boundary waters canoeing for the weekend.

BB.

Re: Looking for feedback

Part of that may be due to the voltage when powering the load directly...

For an approximation, the output current of a solar panel is fixed by the level of sunlight (power) on the front of the panel.

If you drop the panel voltage down because of the load, your current will be closer to Isc (short circuit current) which is 10% or so higher than Imp.

You do not have a charge controller with its own current meter--but many solar charge controllers over estimate output by 5-10% (or even upwards of 30% at times)... It is not that these are "bad" charge controllers--It is just accurate current measurement is worth them spending extra money for more exacting measurements. And what customer would be unhappy that his system is performing better than expected.8)

Using an external Amp Meter (or current shunt) for accurate measurements--like you are doing--can be important to understand what is really happening to the system.

-Bill