Adjusting BMS Battery Charger Cut Off Voltage

Batteries, Chargers, and Battery Management Systems.
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jase1979   10 mW

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Adjusting BMS Battery Charger Cut Off Voltage

Post by jase1979 » Aug 10 2019 9:56am

Hi,

I have a new battery and want to use my old charger from BMS battery. My new battery is 14s, to requires a voltage of 58.8V.

I previously had a 12s setup. I found out that the voltage on these charger can be adjusted via a trim pot, however my charger maxes out at 56V.

Can I modify the charger, trim pot or near by resistor to increase the voltage to 58.8V?

Thanks in advance

The charger is similar to this photo inside:

Image

john61ct   100 kW

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Re: Adjusting BMS Battery Charger Cut Off Voltage

Post by john61ct » Aug 10 2019 11:29am

56V ÷ 14S = 4.0Vpc

if you don't mind sacrificing a bit of range, that would certainly be good for longevity.

How much lower the SoC, will depend on how long the charger holds Absorb/CV stage, won't sacrifice much at all if it holds until trailing amps fall lower than 0.01C,

if it just charges **to** 56V and stops (CC / Bulk stage only, no CV) then you may have 10-15% lower range or so,

CC-load discharge testing using a precise timer will tell you precisely, don't trust an Ah counter.

Another caution, running a cheap charger at the maximum voltage it can be trimmed to, may be stressful enough to shorten its lifespan.

And you will need to find another way to get cell balancing done, adjustable BMS, a balance charger or other non-BMS balancing gear.

jase1979   10 mW

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Re: Adjusting BMS Battery Charger Cut Off Voltage

Post by jase1979 » Aug 10 2019 11:38am

Thanks for the reply. Yes I was concerned about the BMS not balancing the cells. As I've read that most of the BMSs don't start to balance until 4.2V.

john61ct   100 kW

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Re: Adjusting BMS Battery Charger Cut Off Voltage

Post by john61ct » Aug 10 2019 1:35pm

You could overcome that problem most easily by getting a charger that is easily voltage-adjustable.

So going to vendor-spec over-voltage for balancing purposes could be an explicit occasional maintenance routine, like old-school equalizing a lead bank.

Or even better, a BMS with both an adjustable start-balance voltage, and

a decent balancing-bleed current rate, certainly over 1A, ideally say 6A.

Another alternative is exposing the per-cell (parallel group) connections to external "balance leads", and using a "hobby" balance charger to get a perfectly balanced charge every cycle at whatever termination voltage you like.

Your choices of quality chargers would be a lot wider splitting that 14S with a midpoint tap for the bulk-charge leads, in effect two 7S packs in series.

And finally, there are dedicated balancer gadgets that can be run as needed, at whatever layout, whatever voltage, in theory could be hooked up to work at all times.


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TommyCat   100 W

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Re: Adjusting BMS Battery Charger Cut Off Voltage

Post by TommyCat » Aug 10 2019 2:06pm

john61ct wrote:
Aug 10 2019 11:29am
Another caution, running a cheap charger at the maximum voltage it can be trimmed to, may be stressful enough to shorten its lifespan.
+1

A voltage increase such as this may reduce the amperage capabilities to near half. Use the wattage and math...
But I see the other two pots peeking out, and this too could be adjusted. Take a close look at this thread for tips on operation and adjustments of chargers...

https://electricbike.com/forum/forum/kn ... d-advanced

My advice would be to get a proper charger for your new nominal voltage that has settings for 80,90, and 100% charging capabilities.

Example... https://lunacycle.com/52v-3amp-luna-mini-charger/


Regards,
T.C.
See my completed Magic Pie V5 rear hub E-Bike build Here!

john61ct   100 kW

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Re: Adjusting BMS Battery Charger Cut Off Voltage

Post by john61ct » Aug 10 2019 2:06pm

Relevant other thread
viewtopic.php?t=101750

john61ct   100 kW

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Re: Adjusting BMS Battery Charger Cut Off Voltage

Post by john61ct » Aug 10 2019 2:10pm

Grin also makes Satiator, great adjustable chargers

https://www.google.com/search?q=site%3A ... in+charger


999zip999   100 GW

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Re: Adjusting BMS Battery Charger Cut Off Voltage

Post by 999zip999 » Aug 10 2019 3:37pm

Are those 63v caps ?

jase1979   10 mW

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Re: Adjusting BMS Battery Charger Cut Off Voltage

Post by jase1979 » Aug 11 2019 2:27am

This is my actual controller, the earlier image is a similar controller.

https://drive.google.com/open?id=1wZwlm ... xUQTtAb7ZQ

jase1979   10 mW

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Re: Adjusting BMS Battery Charger Cut Off Voltage

Post by jase1979 » Aug 11 2019 2:33am

Apologies, I meant charger.

jase1979   10 mW

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Re: Adjusting BMS Battery Charger Cut Off Voltage

Post by jase1979 » Aug 14 2019 3:01pm

Maybe I should have changed the title. The charger I have is from the website called "BMS Battery". So this post is nothing to do with the BMS as such.

I want to adjust the charge voltage output for 14s. I can only get it up to 56V. The trim pot has then reached its limit. Is there anyway I can increase the voltage? I've seen a few threads of people increasing the voltage on his style of charger. They seem to have a much greater ranger.

Thanks again for all the previous replies.

john61ct   100 kW

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Re: Adjusting BMS Battery Charger Cut Off Voltage

Post by john61ct » Aug 14 2019 9:29pm

Likely not, either upgrade or look at DC-DC converters, might cost even more.

But the good news is that voltage, 4.0Vpc is perfectly fine for 14S, in fact will greatly increase longevity without losing much range at all.

But you need to make sure per-cell balancing's getting done, one way or another.

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