[SOLVED] UPS charging circuit on bigger battery

[kleintoren]

Hi

I am running a 12v UPS that used to have a 12v 7Ah battery of a car battery - can I use the charging circuit on the ups to charge the car battery or should I use a separate charger?

 

[tpetar]

UPS charge that battery with current of 0,7A and car battery is much larger and need C/10 (55Ah 5A). You need additional charger. Just make float charger with current limiter and this will be fine.

But you should know that car battery is not designed for that purpose, its float battery. Its not designed to deep cycling, for that purpose is lead acid deep cycle battery. You can just kill your battery with one cycle to 10,5V. And one more thing capacity of battery is given for at least C/10 discharging rate (55Ah that mean 5,5A current draining for 10h time, when battery is new and 100% healthy).

UPS design and construction must be good to allow working on prolonged time. Often small standard and cheap UPS (about 50eur) is designed to work about several minutes in inverter mode, they have small heatsink, no forced cooling, and other parts are designed to give backup time in several minutes, if you prolong working time you should consider adding bigger heatsinks on MOSFETs and adding fan coolers to circulate airs.

 

[kleintoren]

Awesome. Thank you for the info - will look into getting deep cycle battery, and start building the charger

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Got a Willard 722 - leisure battery lead acid, wet cell - Made for solar use - how far can I cycle this type of battery, 50% be ok?

On the UPS can I remove the mosfets from the board and mount them on a heatsink and link them with suitable wire to the board?

 

[tpetar]

Awesome. Thank you for the info - will look into getting deep cycle battery, and start building the charger

- - - Updated - - -

Got a Willard 722 - leisure battery lead acid, wet cell - Made for solar use - how far can I cycle this type of battery, 50% be ok?

On the UPS can I remove the mosfets from the board and mount them on a heatsink and link them with suitable wire to the board?

If solar then probably is deep cycle battery. You can discharge it completely. They have smaller starting current and holding current unlike the started lead acid batteries, and therefore battery bank must be properly dimesioned.

Yes, you can remove MOSFETs from PCB and mount them on good heatsinks, but dont use long wires. Use silicone grease between MOSFET and heatsink.