ebike charger min starting charge vol

[marce002]

Hello

I would like to know how to fix this issue. My charger 30vol does not detect battery if not almost full discharged.. if the battery is half discharged eg 3.7v per cell it does not turn led red on (means charging) remains green .... is this fixable?

 

[amberwolf]

It's probably not the charger, it is probably the BMS not enabling the charge port.

With the charger connected (and then with it disconnected), what voltage do you read on the battery charge port when it doesn't allow charge , vs the voltage on the actual battery inside (not the BMS)?

And what voltage on each of these do you read when it does?

Correctly-designed chargers usually have a detection circuit for how much current is flowing from them to the battery, and a lower limit on how much current can flow, below which the charger turns off. (this is why it turns off when charge is done).

If the BMS charge port is off, current can't flow so the charger won't turn on (or will turn on for an instant then back off).

The charger may also have a safety for a minimum voltage before it will start charge, so if the port is off it won't read the battery voltage, and so won't turn on.


As a test you can connect the charger to the battery's *discharge* port instead, when it does not work on the charge port, and if the charger starts up this tells you the charger is fine but the BMS has not enabled the charge port. You don't want to keep charging this way, but just for a momentary test it is ok.


The BMS might be disabling the port because it detects a problem such as cells that are too different in voltage from the others (some do this for 0.1v difference or more). Normally this difference gets worse the further discharged cells get, but that couldn't be the case for yours or it wouldn't enable the port when the battery is empty vs half full....

So, I don't know why it would be doing this, but that's almost certainly the BMS vs the charger.

FWIW, I have a Luna mini pack from a long time back that has a BMS with some funky bug in it's firmware where it does something similar to yours, but it's problem is when the battery is just barely discharged, nearly full--it won't charge unless I discharge it a bit more first. (not very much, just a little).

 

[marce002]

sorry but no bms here it is a custom made pack 4p7s. the charger is not red led unless i have 3.25 per cell line... so my question was directed to some kind of pot or component hack inside the black charger brick that i can touch to enable charging.... this is not for a bike battery and will not balance cells this time

 

[amberwolf]

Well, that's the thing about asking a different question than the one you want answered...you get an answer for the quesiton you asked.

I would recommend that you post the complete details of the situation, including the exact equipment, parts, and wiring you are using, and the complete question you want answered, and then we can see what might be going on.

If you want questions about the internals of a device answered, you have to provide the details of the device including good clear well-lit high resolution pictures of the internals of the device.

Without knowing all those things at minimum, it's probably a waste of time to try guessing further.

 

[marce002]

amberwolf yes you are right... i will prepare the whole material and get back...

(everything is working fine with my homemade 18650 battery pack 4p7s... only issue is the charger *common chinesse 30vol black* starts to charge red led only if the battery is almost depleted (at 3.1vol x cell) else led green no charging!!..
Supose bat is full ... then use the bike 4long ride.. and keep only 25% remaining .. the stupid charger thinks it is charged!! i need to go again until 10% aprox...so it "see"" the battery

 

[marce002]

i will try to take appart and upload internals

 

[E-HP]

Can you get a voltage reading from the charger output when not connected to the battery?

 

[marce002]

Can you get a voltage reading from the charger output when not connected to the battery?

yes sure it is 29.9v

 

[E-HP]

yes sure it is 29.9v

So when you connect the battery, does the voltage immediately drop to the battery’s resting voltage, or somewhere in between? (Measuring at the xt connector)

 

[amberwolf]

Well, the charger itself says it's output is 88VDC at 2.5-2.8A, in that image you posted. It also says it's a 24v charger...so what exactly it is and what exactly it's designed to do are unknown based solely on that info.

A search for the charger p/n SHC-8100LB comes up with numerous links for 24v chargers, so that's probably what it really is; why they would label it as 88v output I cant' figure out.

If there is no BMS on the battery, just direct connection from the cells to the charger, I don't know why the charger would not operate until the battery voltage is all the way down to 21.7v.

Many chargers are typically designed to start trying to charge as soon as there is a current detected on their outputs greater than their shutdown current (which is usually a few mA).

Meaning, as soon as you put a battery that is a lower voltage on it than the charger's unloaded voltage, that difference in voltage will cause current to flow. The charger will sense that this is happening and change it's status light to charging mode, and current will flow until the difference is negligible, and current has dropped below the shutdown current, at which point the charger disconnects the output from it's internal voltages (or turns off it's output switcher so it isn't creating any voltage).

When it detects that voltage is no longer on the output (from the battery connected there) then it will turn it's output back on, and wait for the battery to reconnect (current to resume).


Some are less complicated than that and just always output the voltage they list, simply limiting current to some maximum amount.

Some are more complicated than that and actively communicate (via separate wires) with the BMS in the battery, or do other specific sensing such as only starting charge if a battery is *above* a certain voltage *but below* it's maximum voltage, so that it does not try to charge a failed battery, or one that is not intended to charge to the voltage the charger can output, etc.

 

[marce002]

E-Hp: 88vdc is a label error. if connect the battery it depends as i ve said... if it is 3.1 x cell it is charging and 30v is there if not is floating...

amberwolf: i think some smart circuit is inside detecting a min volt to start the charge.. problem is that if you connect a half discharge or less battery it wont charge unless is really depleted. also if yo put it depleted and leave for two and half hr it charged ok but quite warm... if you put it at 10% aprox it works but if you let charge for 5 mins only and unplug the charger then it wont charhe again bevause in 5 mins the volt increase ruined the operation... ( of course the battery was not charged for 5min!)