Reducing 55V charger down to 54.6V

I think this title may be a winner.... Here's my problems
[*] Cheap 1.5A 13S charger has a resting voltage of 55.0V. I've confirmed that the cc stops when the battery hits 55v on the charger and trips into cv mode.
[*] Charger basically overcharges each cell to 4.23V and typically the voltage reaches the tripping voltage on the bms and the bms cuts the power before the charger can switch to cv mode.
[*] I need to reduce the voltage output down to 54.6V resting so that cv mode kicks in without tripping the bms to cut the charge voltage

How can I do this? There's no pot to adjust the voltage on the charger. Can I add a pot to the output line to decrease the voltage?

I basically want to figure out how I can charge the battery to its balance voltage. I believe the bms kicks in to balance around 4.16V per cell...so I'm wonder if there's a way where I can reduce my chargers voltage to go from cc to cv once it hits that 54.6V number or even slightly below that so it doesn't overcharge the cells... I really don't know how a pot works to reduce the voltage..im sure it's a variable resistance that does this? Would I be able to get one big enough to reduce the voltage by 0.4V without blowing the thing up?

large diode in series will drop .7v

kcuf said:

large diode in series will drop .7v

Click to expand...

Like 1 schottky diode?
Looks like I can get them rated for 60V / 5A. That should be good right?

not fan of schottky for job

p-n cheap and durable t10a100l

charge current determines max amp

do not cut leads when pushing amp limit

I'm not sure I understand your English...

From where I sit I can just add in line to the positive out from the controller a schottky diode and it's low enough current that it'll drop my voltage to the pack from 55V to 54.7v....

no previous mention controller

suggest t10a100l for 10a charge

schottky if you want

not what i would use

kcuf said:

no previous mention controller

suggest t10a100l for 10a charge

schottky if you want

not what i would use

Click to expand...

OK I think I know what you mean. I think I'm comfortable with the 100V schottky. I only need a slight adjustment to the charger so it prevent the bms from shutting off the charge. I'm only ever getting 1.5A so it doesn't make sense to get a 10A diode. I'll order some tonight.

This post causes some concern with this diode approach. I have not tried diodes in this manner to verify...

https://electricbike.com/forum/foru...in-after-charging-a-concern?p=52712#post52712

It's the continue to charge part. Would that be a problem? :?

My old lead acid charger has a diode on the output. I'm going to check that to see if I can use that instead!

Lol just checked it and it's a SR5100 schottky diode! Well see if it does its thing.

Is the charger in an aluminum case, so you can pop the cover off? If so, then there's likely trim pots to tune the output. If so, commonly the pot closest to the output cable adjusts the top of charge voltage.

Could use a buck transformer see photo.

I’ve increased current in one charger, although never tried to drop the voltage. Inside there should be three trim pots, voltage, current and final current at near end of charge.

I already said there isn't a trim pot on it....at least I thought I did. I wish it did... Like I said I've got a sr5100 schottky diode so I'll wire that up in the am hopefully and see what I get. I know the direction of the diode I just am not sure if it matters if I wire it t the negative or positive...

The Schottlky diode worked perfectly well in my case. Smaller foward voltage drop of the Schottky compared to regular diode means less heat is dissipated. You can put it on either side, so as long as the diode sits in the right direction and lets de current flow. I doesn't change anything.

Details: https://endless-sphere.com/forums/viewtopic.php?f=14&t=98771#p1446444

Matador

Oh oh oh yes!!! It works!!! Absolutely perfect too!





I need to build the wire mesh housing for the charger tonight and mount the ammeter. I've got a 12v and 5v buck step down converter coming that'll power the meter and a small fan. For now I'm using batteries to power the meter instead since it can't take 55V.

With the shottsky diode I get a max voltage of 54.8V so by the time the bms takes over it'll be slowly trickle charging while the bms is balancing which is exactly what I want...there really shouldn't be any overcharge with this charger now. Now I can pitch my old charger! Woohoo!

Alright! We're in business!

So I made the wire mesh frame for it but for the edges I can't join the pieces...right? I can't solder the steel together? Maybe I should try. But anyway I was able to fix a broken usb charger that converts 56V down to 5,2V which is enough volts to power the meter andddd a small 40mm fan at half speed, which is perfect for noise. So now I've got this charger working great! I also liquid electrical tapped everything I could and I believe it is finished.

It took 12 hours to recharge my battery from almost fully depleted..Oh boy. Lol. I'm essentially recharging 2900mAh cells at 0.2A each... Takes forever but it'll also help the battery last longer with the slow charging!

The fan provides just enough airflow to cool the components some and keep things in check. It's also completely silent which is excellent! I'll get some pictures later.