Thor Forums

[dkoldman]

Originally Posted by dkoldman

I agree modification are a personal choice. I was trying to show that cheap fixed voltage chargers can harm batteries in rare cases. The points you make a valid. For all antimony alloyed flooded batteries here are Trojan's recommendations. As a side note, I went out to exercise the generator this afternoon the ambient 98 F and the sun was shinning on the right side of the coach, The temperature of the two batteries in the compartment was 118 F.

4. How much should I compensate the charge voltage for temperature?
Temperature will affect voltage readings. As temperature increases, voltage decreases. Conversely, as temperature decreases, voltage increases. Here are the relationships:
Trojan recommends using the following: For every 1º F below 77º F add 0.0028 volts per cell or for every 1 C below 25º C add 0.005 volts per cell to the charger voltage setting.
1: A 12 volt battery @ 70º F. The recommended charging voltage at 77º F is 14.8 volts. The adjusted charging voltage is 14.8 + (6 cells * 7 degrees below * 0.0028) = 14.92 volts.
2: A 12 volt battery @ 21º C. The recommended charging voltage at 25º C is 14.8 volts. The adjusted charging voltage is 14.8 + (6 cells * 4 degrees below * 0.005) = 14.92 volts.
For every 1º F above 77º F subtract 0.0028 volts per cell or for every 1º C above 25º C subtract 0.005 volts per cell to the charger voltage setting
1: A 12 volt battery @ 85º F. The recommended charger voltage at 77º F is 14.8 volts. The adjusted charging voltage is 14.8 – (6 cells * 8 degrees above * 0.0028) = 14.67 volts.
2: A 12 volt battery @ 29.5º C. The recommended charger voltage at 25º C is 14.8 volts. The adjusted charging voltage is 14.8 – (6 cells * 4.5 degrees above * 0.005) = 14.67 volts.
5. Is there a maximum temperature for charging my batteries?
When charging lead acid batteries, the temperature should not exceed 120ºF. At this point the battery should be disconnected from all charging sources and loads in order to cool before resuming the charge process.

__________________
Jim & Roy Davis
2016 Hurricane 31S
1961 Rampside in tow

So here is how I am interpreting what Trojan says and what my existing converter can do

Easy first ( max temp). If actual battery temperature exceeds 120F, then no charging should occur. So I can assume if ambient temperatures reaches 110F, then I can make sure the charger is OFF via no shorepower / generator, or flip the breaker for the converter.

Based on above, the concern appears to be around ensure voltage is not to high as temperature increases. It looks as if Trojan uses 14.8vdc as it it's boost voltage? In my case my max voltage is 14.4vdc so for all ambient temperatures less than 110, I never will have voltage too high.

77F seems to be point of distinction between being hot or cold for Trojan? I would love to see the actual algorithm used by temperature controlled chargers, because as I understand it, the colder it gets the more voltage is expected so I fail to follow or understand what would be the issue with the Storage, Normal or Boost charging stages when temperature of actual battery is under 77F?

What am I missing? Right now it seems like as long as ensure my battery is NOT charging when it is 120F I am good.