Temperature Compensation Issues

[Tom in NH]

My Trace C40 controller has the temperature sensor plugged in and that causes automatic temperature compensation in the charging algorithm. The problem is the charge voltage goes up over 15 volts -- enough to give my inverter indigestion and it shuts down until the voltage drops.... and I have to reset my #!*ing clock radio again! Does anybody else have this problem? Is there a solution that will allow me to still give my batteries an extra shot when it's cold outside? --Tom

[jimjjnn]

Try a battery powered clock or self setting one that uses WWV time signals out of Ft Collins, Colorado

[richhagen]

I realize your probably trying to maximize the state of charge in your batteries, but why not just adjust the bulk and or float voltages down to prevent the high voltage conditions using the potentiometers in the C-40?  Rich Hagen

[srnoth]

Hi there,

When reading your post, something seems wrong. Lets say your average float voltage is around 13.7v, and the charger increases the charging voltage to lets say 16v, the voltage at the batteries is never supposed to instantly jump to over 15v. For example, I have a homemade ~20amp battery charger, that will raise the voltage on a small UPS battery to well over 16v in a matter of seconds. However, when I charge a large 85amp/hour deisel truck battery with it, it puts approx 20amps into the battery, but the voltage at the battery takes quite a long time to move from 12v to 13v. Yet, at the 12v contacts on the charger, the voltage is at that point a little over 14v.

So I have two questions:

1. How big is your battery bank because it will take a lot of amps to raise the voltage in a large battery bank to over 15v from a float volage of 13.5?
   
2. Where do you have the inverter connected, at the Charger or at the battery, because due to voltage loss in the connecting wires, the voltage at the charger may be higher than that at the battery bank.
   
   

So, if you connect the inverter at the battery bank, the voltage that the inverter reads will take a long time to go over 15v, even if the charging voltage is more than 15v.

Also, if you go over 15v on a battery bank for very long, it can damage the batteries, not to mention the various devices connected to them like inverters. Is this really how the charge controller was designed to work? Mabye you should disable the temperature compensation?

[ghurd]

Hi Tom

Sounds like the batteries and controller are outside?

How about moving them inside, where the charge voltage won't need to get to 15 volts?

G-

[Chuck]

Hi Tom,

I'm wondering about how you have the c-40 set up. Is it set for charge control and wired for load diversion? Do you have a dump load attached ? If so is it working ?

From experience I know that if you have the c-40 set for diversion and you don't have a diversion load attached, that once it reaches float level it will dump all the incoming power back into your battery. In other words, it won't control at all. Make sure you have it wired properly for charge control mode if you don't have a working dump load attached. It's kind of an odd "feature" of the c-series chargers.

It also may be that your batteries are getting so cold that the temp compensation is just getting the voltage too high for your inverter. To lower it all you have to do is unplug the temp sensor. You'll be back down to (non-compensated) specs in no time.

Chuck

[Tom in NH]

Wow. Thanks everyone for your comments. Yes, the batteries are outside. There are 375 amp hours worth. The overvoltage problem only crops up when the grid charger is nearing the end of a charge cycle, after about 10 hours. Rich, (BTW that was me on ebay) I guess I didn't realize the pots would adjust the voltage when the automatic temperature compensation was in effect. I guess that's worth a try. Smoth, the need for more than 15v is not due to any kind of line drop. I have everything real close. The batteries are right underneath the solar panels and the inverter and switching circuitry are in a separate compartment right next to the batts. The need is apparently entirely due to the C40 temperature compensation scheme. Assuming some figures I got at http://www.uuhome.de/william.darden/carfaq.htm are correct, the C40 is probably looking for 1.58 volts over the bulk voltage when the temp is around zero deg. F., or approximately 16 volts. Another comment in the carfaq site (great place to learn about lead/acid batteries BTW) was, "Cold reduces capacity, heat kills." Maybe I should be more concerned with temperature compensation in the summer heat and less concerned in the winter cold. Here's a pic of my setup if anyone's interested. One cable brings AC into the house. The other brings household current to the backup charger. Soon I will be adding six more panels of about 100 each. They're in the construction stage now.

[ghurd]

If its cold, the V must go up to get the battery charged.

A control V of 13.7 won't do any real charging at 32'F, so the battery will never get full.

It would probably be best to get the batteries inside.

G-

[richhagen]

The pots still adjust with the Temp Comp. in place.  You still need them for example to adjust for the difference in charging voltages between different types of batteries.  Rich Hagen