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first time asker so be gentle if this is dumb.

I'm using this LED Driver (constant current, output range 143-286v) to balance charge a high voltage hybrid vehicle battery at very low current, and it works pretty well. I've got a diode on the output to prevent back feed from the battery, a dropping resistor to bring the output close to the battery's nominal voltage as well as a 100k Ohm resistor between the positive and negative terminals to bleed off residual charge in the output line when I turn it off. So far, so good, right? Right?

The thing is, recharge times are very slow as the current is so low. For one thing, I want to sometimes discharge the battery below 143V. I can use the driver I have now, but it operates in a hiccup mode when output voltage is below 143V, which makes things go pretty slow. Second, for balancing I really only need to be using such low current when I'm nearing full charge in the battery.

So I'm wondering, what happens if I add a second power supply, say this one (constant current, output range 72 - 214v) in parallel with the first one (again, with a diode to prevent back feed).

My thinking is that when the battery is at lower voltage the second, faster supply will be working until it reaches it's output over voltage protection and shuts off until power cycled, leaving just the first supply to finish the charge slowly. In general, the lower voltage charging phase can be at just about any current, it's only important that the current be limited to about 350mA when the battery voltage is nearing 240v, or in this case, with the second charge mentioned, the max output of 214v. It would also be nice to have that lower range of output voltage from 72v to 143v that is so spotty with my current supply.

Are there a few more pieces to the puzzle I need explained to me to make this concept work? Should I just not try anything of the sort? I've read up quite a bit on the subject and most sources seem to indicate its not a great idea, but they're pretty vague about why and seem to be for very different applications. A lot of the concern seems to be about imbalanced load sharing / back feeding / etc.

Since these LED Drivers have pretty robust Over Voltage Protection and I can add diodes wherever needed it seems, intuitively, like it should work fine. However, my intuition is often wrong when it comes to electrical. Again, the only time that output current and voltage is super important is at the top end of charge, which should be AFTER the second supply has turned off from over voltage.

If this would generally work, there's a range of voltage from about 143v-214v where both supplies would be within their output range. Would the total current supplied to the battery be the sum of both output currents?

Thanks for the help!

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  • \$\begingroup\$ Why can't you use a proper charger for that? \$\endgroup\$
    – Justme
    Commented Jun 17, 2022 at 0:10
  • \$\begingroup\$ Not totally sure what you mean by this. But essentially looking for a low cost way of achieving a constant 350mA at the top end of charge while allowing higher current charging for the bottom end of the charge cycle. There really aren't a ton of proper 250V DC chargers on the market, from what I can tell, certainly not that allow adjustable current, unless I am mistaken. And of course, cost is a factor. Given the choice between keeping my current set-up and upgrading to a $500+ piece of hardware I'll just stick with what I got. \$\endgroup\$
    – Derek Hershman
    Commented Jun 17, 2022 at 1:00
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    \$\begingroup\$ Amateur battery charger design. What could go wrong? At least they're not lithiums. \$\endgroup\$
    – Harper - Reinstate Monica
    Commented Jun 17, 2022 at 2:06
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    \$\begingroup\$ To be clear- there is battery cooling control, high voltage dc circuit breakers, quality voltage and current measurement etc. included in my current setup. My current setup works and has worked quite well! There's nothing going wrong. If you see an issue with my two power supply thought process though, by all means do point it out please. But I'm not just wiring an led driver to a high voltage battery willy nilly. \$\endgroup\$
    – Derek Hershman
    Commented Jun 17, 2022 at 3:11

1 Answer 1

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Would the total current supplied to the battery be the sum of both output currents?

Yes. Each supply will output current until reaching its maximum output voltage. The total current going into the battery will be the sum of the two currents, with each supply acting the same as it would alone at the same output voltage.

I can use the driver I have now, but it operates in a hiccup mode when output voltage is below 143V

This will still happen with two supplies, but for much less time because the other supply will raise the battery voltage quickly.

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  • \$\begingroup\$ Thank you! As far as the hiccup mode- I understand that. So essentially, from 72v-143v the second supply would be fully on and the first supply would be hiccuping, meaning that my current might jump around a bit but should mostly be around 700mAH. Then from 143-214V both drivers would output and my current would be about 1A, and then above 214V the second driver would shut off and only the first driver would output, resulting in a current of 350mA? \$\endgroup\$
    – Derek Hershman
    Commented Jun 17, 2022 at 1:22
  • \$\begingroup\$ Yes, that's it! \$\endgroup\$
    – Bruce Abbott
    Commented Jun 17, 2022 at 1:33
  • \$\begingroup\$ Thank you so much Bruce! Are there any other complicating factors I should keep in mind or can I go for it (with the obvious caveat that if anything goes wrong I will in no way hold you accountable)? \$\endgroup\$
    – Derek Hershman
    Commented Jun 17, 2022 at 1:35

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