Baby, It’s Cold Outside

(I wrote this in December and somehow it did not get posted until April!)

This morning it was about 50 degrees. Tomorrow morning we are expecting 28. The constant temperature swings make it difficult to dress. Layering is the key.

Temperature changes affect your solar power system, too, particularly in battery charging. Is there any action you need to take? Depends.

Lead acid batteries, sealed or flooded, need a higher charge voltage in cold weather. If your charge controller or inverter/charger has a temperature sensor that sticks or bolts to your battery, you’re maybe ok. And when I say battery, I mean the total pile of cells, not just one casing holding one or more cells. Ideally, they are all behaving the same and have about the same temperature. You won’t have a sensor for each one. It doesn’t hurt to spot check them all with an infrared thermometer once in a while to be sure.

Only one of my many charge controllers has temperature compensation, so I have to do a little manual intervention as the weather changes. It takes a while for tons of lead to cool down. Longer if you have an insulated battery box or cabinet. I don’t.

I go out to my Man Cave/Control Room most evenings to watch movies, read or work on projects, so I keep up with the meters. Lately they have been running a little low. I have a temperature chart for my batteries and it shows my settings are a little low. I just bumped up the charge voltage to 59.9 volts for the highest setting, maintaining the float at 54.4. At some point, my inverter complains of too much voltage, so I go with the minimum settings. I can hear the golf car batteries sizzling in the jalopy in the afternoon, but the main bank is holding higher at night, keeping my hand away from the grid switch.

It is a delicate balancing act. If I boil the AGM bank I will kill them. If I run them too low, I shorten their lives. If I switch to the grid, what’s the point in having solar?

The system is getting an upgrade. I recently acquired my own mobile solar generator trailer, similar to the one in the Turbo Beast blog. It has been interesting to explore its wonders and integrating its components into my home system will be a big upgrade. The mobile system has a Midnite Solar MPPT charge controller, a pretty nice charger, but the real star and boss of operations is a pair of 6048 Sunny Island inverters.

It appears that all charging runs through the SI pair. It keeps up with State of Charge and controls an automatic diesel generator. The other night I forced the battery down with heavy loads. The generator started and before it was over the battery voltage had soared to 62 volts! A previous run had gone to 60.8 volts. The difference was the temperature. These are flooded forklift batteries on the trailer and have different needs than the AGMs in the Solar Shed. I will have to change the settings when the Sunny Islands and the Kubota genset are attached to the Shed, but then it will all be automatic.

I do not offer any settings or charts for you, here, because batteries are not all the same. These days you can find detailed data sheets online for most batteries. If you can’t find one for your particular battery, try another brand of similar type. For example, a generic golf car battery like the Sun 230 has specs similar to a Trojan T105 or Energizer GC2. My big AGMs were marketed for standby use and had no specs for cyclical use, so I had to borrow data from another brand.

I do not recommend mixing battery types, but I do it myself. I am evaluating a big pile of AGMs for the Solar Yacht project, I have flooded batteries in my electric farm vehicles and, soon, I will add the 2 tons of forklift batteries from the mobile unit. In this case, the AGMs are the fussiest and most expensive, so I will go with their settings and pull the flooded batteries off to the side from time to time to give them a desulphating charge that would kill the AGMs.

If you put your own system together you should know if you have temperature compensation built in. If not, ask your installer or do a little snooping. A temperature sensor cable usually plugs in or screws to a terminal block marked something like “temp.” All that I have seen have used a thin round wire or flat cable, similar to “modular” cable used on real telephones. Remember those? At the battery end the sensor will be embedded in a piece of plastic that sticks to the battery or in a ring terminal that connects with the battery cable.

Yes, the shorter days and winter gloom could be hurting the performance of your system, but it could also be something as easy to change as a charge setting. When in doubt, read the manual!–Neal

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