I have a question about using a charger that can supply more than 15A to an AGM battery. I’m designing the electrical system for my project boat and want to resolve a concern. Here’s the scoop…
I have a small camper for my truck. I normally keep it plugged into “shore power” while being stored off the truck. This fall I discovered that it had been unplugged for almost six months and the nine year old AGM house battery (Powersonic PS-121000U 12 Volt, 100 AH) was dead. I plugged the camper back in and walked away. A couple days later I opened the camper and was greeted by the smell of hydrogen sulfide. I immediately unplugged the camper and left the door open to let things air out. An hour later I went in and examined the battery, which was still almost too hot to touch. It had swelled and the case was cracked at the top, allowing gases to escape.
In summary the battery died due to thermal runaway. It was charged too rapidly and became overheated. The Powersonic tech told me that, in general, their AGM batteries should never see more than a 10A charging rate, although up to 15A was OK for very short periods. When asked why I had no problem until last fall, given that the camper had a Magnetek 45A charger, he said that because the battery was never discharged very far, the voltage differential between the battery and what the charger was presenting, combined with the relatively high internal resistance of a healthy battery, limited the rate at which the charger was charging.
However, given that I had allowed the battery to reach a very low voltage, the charger started dumping a lot of current into the battery, which raised the temperature of the battery, which lowered its internal resistance, which allowed even more current to flow, which raised the temperature of the battery even more, which allowed even more current to flow… until the battery became so hot that it swelled up and cracked its housing. Hence the term, thermal runaway.
Given what the Powersonic tech told me, I replaced my camper charger with a three-stage 15A charger (Powermax PM3-15LK) to prevent this from happening again, even if the AGM battery becomes completely discharged again. Given that I got good life out of the previous battery, I replaced it with the same one.
Now I’m looking at batteries and a smart charger for the boat, and am reading that people are using three stage chargers rated at more than 15A for stage one, even with an AGM battery. Can these chargers potentially cause an AGM battery to go into thermal runaway if the battery is allowed to reach a very low charge?
I have a small camper for my truck. I normally keep it plugged into “shore power” while being stored off the truck. This fall I discovered that it had been unplugged for almost six months and the nine year old AGM house battery (Powersonic PS-121000U 12 Volt, 100 AH) was dead. I plugged the camper back in and walked away. A couple days later I opened the camper and was greeted by the smell of hydrogen sulfide. I immediately unplugged the camper and left the door open to let things air out. An hour later I went in and examined the battery, which was still almost too hot to touch. It had swelled and the case was cracked at the top, allowing gases to escape.
In summary the battery died due to thermal runaway. It was charged too rapidly and became overheated. The Powersonic tech told me that, in general, their AGM batteries should never see more than a 10A charging rate, although up to 15A was OK for very short periods. When asked why I had no problem until last fall, given that the camper had a Magnetek 45A charger, he said that because the battery was never discharged very far, the voltage differential between the battery and what the charger was presenting, combined with the relatively high internal resistance of a healthy battery, limited the rate at which the charger was charging.
However, given that I had allowed the battery to reach a very low voltage, the charger started dumping a lot of current into the battery, which raised the temperature of the battery, which lowered its internal resistance, which allowed even more current to flow, which raised the temperature of the battery even more, which allowed even more current to flow… until the battery became so hot that it swelled up and cracked its housing. Hence the term, thermal runaway.
Given what the Powersonic tech told me, I replaced my camper charger with a three-stage 15A charger (Powermax PM3-15LK) to prevent this from happening again, even if the AGM battery becomes completely discharged again. Given that I got good life out of the previous battery, I replaced it with the same one.
Now I’m looking at batteries and a smart charger for the boat, and am reading that people are using three stage chargers rated at more than 15A for stage one, even with an AGM battery. Can these chargers potentially cause an AGM battery to go into thermal runaway if the battery is allowed to reach a very low charge?