PWM questions

**stoichiometry** · July 30th, 2011, 16:19 PDT

Hello there!

Since my last post ive put up my panels, wired the cabin and am making ice cubes!!! It's fantastic!

I've a question on batteries and PWM.

So, I've got 220ah 6 volt batteries. 2 strings of 4 (two 24 volt banks)
I'm using a PWM and using 29.2 as PWM voltage.... And I see PWM 10 to 99 percent displayed but I never quite get to float... Why might this be? I've been really careful to make sure all wires are of equal length in the battery bank. Could my PWM voltage be too high or too low? I hear H2 and O2 being made...

Thanks,
M

**waynefromnscanada** · July 30th, 2011, 16:23 PDT

Do you have the link to your last post? And does that last post list what you have for batteries, controller, panels etc? Would help to know that info.

**stoichiometry** · July 30th, 2011, 16:34 PDT

Originally Posted by waynefromnscanada

Do you have the link to your last post? And does that last post list what you have for batteries, controller, panels etc? Would help to know that info.

So-- I'm doing this on a budget, so please don't make fun of my choice in components. It's sort of an experiment in progress-- I'm building a wind turbine too.

Anyway. I've got 6 evergreen Panels. (205watts wired in pairs or 3 strings @ 24 nominal volts and 11.5ish amp max)

8 - gc2 batteries, morningstar pwm60

Does this help?
M

**Cariboocoot** · July 30th, 2011, 16:37 PDT

In addition to what Wayne asked (I actually looked through previous posts but did not find a definitive equipment list other than Evergreen panels);

Got array? About 1650 Watts worth?
Got hydrometer? Nothing beats an SG reading for indicating SOC.
Normal Absorb charge Voltage (PWM is a type of controller, not a charge stage) is 28.8 Volts for FLA batteries. Some (Trojan & Interstate) manufacturers recommend higher.

Without the details no one can be more specific.

**Cariboocoot** · July 30th, 2011, 16:42 PDT

Second post showed up while I was posting.

A little shy on array size at 1230 Watts. Probably takes a while to get through Bulk (depending on how much your using of your 440 Amp hour capacity) and you're running out of daylight before you finish Absorb.

Take one string of the batteries off line for a day and see what happens. Your 11 Amps peak is 2.5% of your battery bank; far below the recommended 5% minimum.

What do I always say? (All together:) "You need more panels for that battery bank!"

**stoichiometry** · July 30th, 2011, 16:59 PDT

Originally Posted by Cariboocoot

Second post showed up while I was posting.

A little shy on array size at 1230 Watts. Probably takes a while to get through Bulk (depending on how much your using of your 440 Amp hour capacity) and you're running out of daylight before you finish Absorb.

Take one string of the batteries off line for a day and see what happens. Your 11 Amps peak is 2.5% of your battery bank; far below the recommended 5% minimum.

What do I always say? (All together:) "You need more panels for that battery bank!"

Thanks- I get through bulk very quickly... My fridge and radio don't draw much ( less than 1000 watts per day). After bulk I get to PWM and the amps slowly drop but it rarely gets o float. It did yesterday ... But didn't today. Perhaps, I'll try a PWM voltage of 28.8 instead of 29.2 ...?

I'll look into getting sg readings tomorrow. (I've got hydrolysis of water.. Fwiw)

Best,
M

More soon,
M

**BB.** · July 30th, 2011, 17:08 PDT

For flooded cell battteries, 29.2 volts is not bad. I would not back down on the voltage setting.

Have to look strong later, but there have been some complaints about morning star controllers set to other than default charging settings not regulating voltages properly... Not sure what models may be affected.

I am posting from my phone so can't search for details at the moment.

-Bill

**RCinFLA** · July 30th, 2011, 17:18 PDT

Six 205 watt panels wired as three parallel strings should yield about 33 amps at max sun.

**stoichiometry** · July 30th, 2011, 17:22 PDT

Originally Posted by BB.

For flooded cell battteries, 29.2 volts is not bad. I would not back down on the voltage setting.

Have to look strong later, but there have been some complaints about morning star controllers set to other than default charging settings not regulating voltages properly... Not sure what models may be affected.

I am posting from my phone so can't search for details at the moment.

-Bill

Bill,

I too am posting from my phone... Hence the brevity of my messages. I wonder if it is because even at idle my inverter draws a bit of current and this is "sensed by the charge controller as a "depleted" battery? I got thru bulk by 9:30 this morning but PWM and various percentages were being displayed all day. I just switched to one of the "standard" programs and will see why happens tomorrow.

Ccboot- I know I'm a bit low on the number of panels. I agree - i would like to have more panels... I figure it's incentive to get my turbine up and running.

Best,
M

**stoichiometry** · July 30th, 2011, 17:25 PDT

Originally Posted by RCinFLA

Six 205 watt panels wired as three parallel strings should yield about 33 amps at max sun.

It certainly does! I get almost 1000 watts in the morning during bulk when there is still dew in the lawn. I just never get completed thru the PWM absorption stage.... Or maybe I do, but Maybe the charge controller or the way I have the inverter connected is causing *funny* readings?!? Dunno?!