Is my solar PV panel open circuit voltage too high?

[veloman]

I am wondering if my 4110 fet controller would be okay with charging my 70v battery, while connected to controller, with a solar panel of 105v open circuit / 87.5v peak at amp max, but RATED at 60v.

I am using 5 "12v panels" in series.

I know the circuit voltage will drop to match the battery voltage, which is safe for the controller. But will there be an instant before that drop in voltage that could harm the controller?

 

[heathyoung]

Nope, not unless your battery is disconnected. If it worries you greatly, put a zener across it.

VOC is also dependent on temperature - the colder it gets, the higher it gets.

 

[e-beach]

I am wondering if my 4110 fet controller would be okay with charging my 70v battery, while connected to controller, with a solar panel of 105v open circuit / 87.5v peak at amp max, but RATED at 60v. I am using 5 "12v panels" in series. I know the circuit voltage will drop to match the battery voltage, which is safe for the controller. But will there be an instant before that drop in voltage that could harm the controller?

Hummmmm.....at what voltage does your controller state is the maximum voltage and/or amperage? What kind of a battery charger are you using and what are it's specs?

I am only asking this because it is possible to put fuses in-line, maybe something like this (http://www.wiringproducts.com/contents/en-us/p4022.html) but if we have a bit more info on your exact controller / charger then it would be easier to say.

 

[amberwolf]

If your pack has a BMS on it that disconnects the pack from the controller at end of charge, and there's no other load on the panels then the controller oculd see that full OCV.

Whether it's too high or not depends on the parts inside. If they are rated at 100V (caps, FETs, etc) then that 5V might be ok, or it might be enough to push them over the edge. Or mabye just enought o degrade them a little each time. Dunno--unfortunaely the only way to find out is to test the theory, and I don't reocmmend that.

 

[veloman]

Here's some more details. My '70v pack' is a 50v a123 in series with 6s Headways (so 22s lifepo4, or 70.4v nominal).

The BMS on the a123 pack does not cut charge anytime other than hitting LVC. No BMS on the Headways. So my circuit will typically have 72-79v going through it, to the controller. The controller is rated to 72v nominal. (cellman 4110 EB312)

My plan was to put a charge plug on the two leads that connect to the controller. (one end is the positive for the a123, the other end is the negative for the headway pack). This is physically closer to the controller than the cells. That's why I was a little worried.

 

[Lebowski]

you just got waaaaay to much sunshine writen from gray skyed Zurich, tiny slowflakes coming down,
my fingers froze solid this morning on the bike man I hate the cold. And then to remember I could
have accepted that job and moved to Austin back in early 2004

 

[Holocene]

Hi, the usual way to work with solar charging is to use a maximum power point tracker (MPPT) in series with your panels. But you've got sorta an oddball battery voltage to work with there, so it might be hard to find the MPPT you need. 48 volts is a common spec since it's used in the Telecom industry to charge their banks of 48v SLAs which power various telco equipment.

Could you split your batteries into two packs by chemistry? That might get you to a pack voltage that you can use with a 48v MPPT. Use as many of the solar cells in series as you need to get max power from each. Have fun!

More on MPPTs here:
http://en.wikipedia.org/wiki/Mppt

Cheers,
Holocene

 

[veloman]

Thanks for the info on the mppt.

I've been charging my bike for 3 days now with my panel, and the controller still works fine. Just have to make sure the battery is plugged into the controller before I plug in the panel.


I could use the 48v mppt on my main battery which is 50v nominal.

 

[John in CR]

What do you have for protection against over-charging your batteries?

 

[veloman]

Nothing at the moment. But I have been at least 5 hours of pure sunlight away from getting near fully charged. It's only 0.3amps max so it's a very slow charger.

I looked into the fetcher limited board, but the seller doesn't seem to have any. I'd like to buy a complete one....

 

[megacycle]

Panels were made to charge multiples of SLA's, eg if you look at the panel it might have 12 in its code.
12V sla solar charging still has some kind of charge control.
So you've got a setup to charge 60V SLA,s @70 V.
Your lifepo4 pack should be hitting the wall at 22x3.4 about 75V.
Lifepo4 is so good for SLA replacement as 4S is approx 12V sla, about 14V charged. 14x5 for 70V.
With 2 over with 22 cells though don't know, it also depends on a lot pack variables different to the SLA anyway.
A Mppt tracker is there to try to keep you at pmax.
As soon as you get close to charged and current is backing off panel volts will head off toward your Voc @100V if you have good clean panels 90 degrees onto full sun on a pleasent to cold day and some cells will end up well over 4V expect if they're anything like A123 im use to.
Like Heath said a zener, guessing for 75V would be good and of course cell balancing.

 

[veloman]

Well, I don't plan to use the panels near the end of my charge, so I'm too worried about the exact voltage. My original question in this topic has been answered.

Though it wouldn't be a bad idea to have HVC to be safe, if I get distracted some day.

 

[megacycle]

Dont know if you have come across cellogs from Hobbyking if you just need alarm when your first cell hits HVC, they are extremely accurate and cost less than a packet of smokes here

 

[veloman]

i have one celllog, though the bike is outside when solar charging.