# Charging small sealed lead acid battery with alternator?



## RazorRust (Aug 13, 2020)

I'm in the process of putting a small pc in my car. My plan was to run an inverter off a small 12v 8ah SLA scooter type battery. I would install a battery isolator relay between the small battery and the main battery. The small battery would only be connected to the main battery when the alternator is charging. The small battery is to prevent the pc from rebooting while I crank the starter.

Will the alternator damager the small lead acid battery?


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## dkc7 (Jan 7, 2022)

If you connect the small battery to a plug that is only powered when the car is running it does the same thing. The small battery will be protected by the fuse. A capacitor does the same thing but I know nothing about capacitors.


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## RazorRust (Aug 13, 2020)

dkc7 said:


> If you connect the small battery to a plug that is only powered when the car is running it does the same thing. The small battery will be protected by the fuse. A capacitor does the same thing but I know nothing about capacitors.


Ah I see. I was going to use an isolator so the starter wouldnt pull from the small battery when cranking. But if there is a fuse that's not hot while cranking then I wouldnt need an isolator or a fuse. I need to check and see.

Will the 75 amp alternator be too much for the small 8ah battery? Does the battery draw less current as it becomes charged?


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## dkc7 (Jan 7, 2022)

An isolator would be the proper way to go. But if your cig lighter outlets only have power when the car is running then starting the engine wont affect the sla battery. Some cars the cig outlet is directly to the battery not hard to check. I dont know enough about charging systems tell you about overcharging. A mechanic or rv shop would know.


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## khlae (Dec 31, 2016)

dkc7 said:


> A capacitor does the same thing but I know nothing about capacitors.


I think you might be confusing capacitors for tweeter protection with other non-equivalent electrical loads? How do you think this would work?


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## dkc7 (Jan 7, 2022)

Im not confused. As I said I dont know a lot about capacitors. Theoretically capacitors store energy. Frequently electric motors have capacitors which help during start up. In a way the sla is being used like a capacitor. The question at hand is wether the sla could be damaged by overcharging. a capacitor has nothing to do with that.


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## RazorRust (Aug 13, 2020)

I think the battery only draws a small amperage when it is charged or close to it. But if the battery is low or dead, it would draw a lot more current. This is when it's important to limit the current. The fuse between the SLA battery and alternator should blow before damaging the battery. 

I found out these SLA batteries are used to power trailer brakes when a trailer brakes away from the tow vehicle. A 12v dc to dc trickle charger is used to keep the battery charged. Amazon.com: Hopkins 20007 Break Away Battery Charger : Automotive . They're cheap enough and should work for my purposes.


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