Battery Maintainer: Temperature Compensation

I bought Victron Energy's Blue Smart IP65 12v charger for its ability to monitor the charge session using a phone (Bluetooth connection), but it is a very well built unit and specifically says about its feature about temperature compensated charging. I think the CTEK also has a specific model CTEK Polar for very cold climate charging, but I don't know about the temperature compensation feature.

Blue Smart IP65 Charger (120V and 230V) - Victron Energy

 

I got my 5A Victron charger for $75 which is cheaper than CTEK Polar.

http://www.amazon.com/gp/product/B07TLCT7X7/

 

Oh, rats. You are in Canada. Yeah, the price can be drastically different across the border. I once purchased a charge port cover from a seller in Canada on eBay. The price of the item was not bad, but the cost of shipping was high, considering it was just driving distance from where I live. BTW, from what I understand, Victron is a Dutch company with international markets. There may be some retail stores near you that may offer a better price.

 

You're just maintaining a 12V battery. You don't need perfect temperature compensation because you don't need to maximize capacity of the battery. It just has to be enough to start the car and keep the battery from being damaged from prolonged low SOC.

I have the non-polar version of the Ctek 4.3, and I like it. It has a snowflake mode that just bumps the voltage up a bit in cold weather. I've never used that mode because it doesn't get that cold here.

The non-polar version lists the output voltage as 14.4/14.7/15.8. I assume that's the max voltage for normal/snowflake/recondition. The polar lists 14.4/15.0/15.8. So the snowflake mode is good for lower temperatures on the polar version. But 15.0V sounds plenty high no matter how cold it gets. I'm sure even charging to standard 14.4 is a lot better than nothing no matter how cold it is.

If you have a block heater (or even if you don't), you could add a heating pad on the 12V battery. I think the ideal setup would be to run a block heater, battery heater, any other heaters, and a battery charger to one junction box, then run a single wire to a block heater plug in the bumper.

Also, note that inanimate objects don't care about wind chill. No matter how windy it is, things sitting outside won't get colder than the air temperature. It matters for people because your body will (hopefully) never reach -30 degrees, so you're always losing heat and you lose heat faster when it's windy, which feels the same as colder air.

 

Oh, that was you. Yeah, thank you for letting me know about the product. I did not have the problem of the weak magnet, I think you mentioned in the thread. The EV Port Cover performed very well under the snow, ice, and freezing rain with very strong winds in my climate.

Fort what it worth, the Victron charger I mentioned above has fully customizable charge settings via a phone app. I have never used the feature for it warns that the built-in battery presets work well. But for expert users, the max current, the charge voltage setting, as well as temperature compensation coefficient, can be changed to user values on the fly.

 

In the manual it recommends to use the snowflake option as a rule, for spiral wound batteries Absorbent Glass Mat’s, like the Optima Yellow Top and a few others. IIRC it charges at slightly higher voltage. If manual is missing you can download PDF to verify.

 

It's more accurately AGM/winter mode. It should be used all the time for AGM batteries. But it can also be used for standard flooded batteries when they are very cold.

"the charge voltage should be reduced by 3mV per cell for every degree above 25°C and increased by 3mV per cell for every degree below 25°C. If this is not possible, it is better to choose a lower voltage for safety reasons."

Charging Information For Lead Acid Batteries – Battery University.

So if 14.4V is ideal at 25C, 14.7V ideal at around 8 degrees C, and 15.0 is ideal at -8 degrees C. But it's always safe to go a little lower in voltage. Based on this formula, charging to 15V at -42C is equivalent to charging to 13.8V at 25C. A little low, but you're still charging.

I think temperature compensation would be important in an application like an off grid battery bank where you need to maximize cycle life and capacity. For cars you just want to get the voltage somewhat close without going too high. If you charge to 14.7 or 15V, that's higher than the car will ever do because I'm pretty sure cars don't have any temperature compensation in the charging circuit.

 

My point is you don't need to get to precisely 14.4V, or whatever the equivalent is at a colder temperature. That's ideal, if it's a little lower the battery will still charge, just not to 100%.

 

No it isn't.
It is an unnecessary complication.

Assuming that the tender was working properly before the cold snap and the battery was fully charged,
at a VERY low temperature the battery requires MUCH less current to keep it charged.
At the temp's you mentioned, very near to zero actually.

Temp compensation can become more important at very HIGH temps but even then it's not that big a deal with a well designed tender.

 

It's not that it won't accept ANY current but that it will be less and will take longer to charge.
AND.....it will appear not to be fully charged because it won't put OUT as much current at that temp, no matter how fully charged it is.

I am glad that you are happy with your "temperature compensated" charger.
I bet that there are a lot of people in similar situations who get by just fine with a model that does not have that feature.