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richie-trent avatar image
richie-trent asked

Buck Boost cutoff for lithium batteries

I see this question has been asked many times but no clear answer.


What is the best way to set up a Buck boost to charge a lithium battery bank, but shut off charging to protect the batteries? Or does it need to shut off? What happens when the batteries reach the preset charge voltage of the Buck boost? Will it just keep charging at its full current?


Our setup is on a Ford Transit van, Buck Boost 50a charging a 824ah SOK battery bank, with Smartshunt and CCGX. We’ve set the charge voltage to SOK parameters, but I’m concerned about overcharging the batteries.


What is the easiest/best way to trigger the on/off relay on the Buck boost to stop charging when the batteries get to a certain voltage?

Orion DC-DC Converters not smart
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2 Answers
Trevor Bird avatar image
Trevor Bird answered ·

Hello @Richie Trent . If the voltage settings are set on the charger correctly, the battery can’t over charge because once the battery terminal voltage of the battery reaches the voltage set on the charger no current will flow. No need to disconnect anything under those circumstances. It’s like having two water tanks connected by a pipe. Once they both have their water at the same level, no water flows.

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richie-trent avatar image richie-trent commented ·
So theoretically the Buck Boost would still be pumping 50a through the batteries but it would all just be going back to ground?
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Trevor Bird avatar image Trevor Bird richie-trent commented ·
No, the voltage of the battery would be equal to the voltage of the Buck boost and no current would flow.
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richie-trent avatar image richie-trent commented ·
@Trevor Bird so I got the batteries to full charge yesterday, then turned the vehicle on to run the Buck Boost. It was putting out less than 1amp, so seems to be working perfectly! Thanks for your help.
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Robert avatar image
Robert answered ·

Hello, the Buckboost has to switch off by the BMS.

There is no other clever way to protect your Lithium Battery from charging when the BMS "said" no ATC.

Battery Temperature is one example.

If you controll the Buckboost ONLY by voltage you Lithium Batteries can easily damage.

Best regards Robert

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Trevor Bird avatar image Trevor Bird commented ·

@Robert I thought the OP said he had an SOK battery bank. This has internal BMS and no access to ATC signal. I also note the following question from the original post

"What happens when the batteries reach the preset charge voltage of the Buck boost? Will it just keep charging at its full current?".


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richie-trent avatar image richie-trent commented ·

@Robert I don't fully understand your answer. Are you saying there is no way to trigger the Buckboost to shut off? I know I can set the Buckboost temperature shutoff but that seems crude. Please offer a solution if you can think of one. Thanks.

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