charger voltage vs battery pack voltage?

[rickpaulos]

What should the nominal charger voltage be for a given battery pack voltage?

Is there a general guideline?   How much over is needed to charge?

Car alternators usually charge at 14.2 to 14.4 volts for a 12 volt battery.  My garage auto battery charger says it's 12 (or 6)  volts on the switch settings  but it measures higher with no load. The meter only shows amps.

Should I just go by the labels and match?

 

 

[null]

Different battery chemistry take different charging phases so I wouldn’t recommend using anything other than a Li-ion charger. (or do lead work the same?)

The voltage measured on the charger should be the same as the maximum of the battery, so 84V for example. (Cell max voltage being 4.2V x20 in serie. Nominal is based on 3.7V?)

Not sure if this answers your question.

Edited December 17, 2020 by null

[rickpaulos]

I took the covers off for photos.  36v pack with 18650 cells.  no mention of chemistry but I'm sure they are li-ion.  The 3 pin connector has 2 reds on one pin and 2 blacks on another pin and the 3rd pin is vacant.  I would think the bcm (battery control module) would regulate charging so the charger is just a dumb ac to dc converter. There are no feedback lines to the charger.    I see some of the charger ports are threaded (this one is) and some chargers have threaded rings to hold the plug in and others are just press in rubber. With all the news of spontaneous fires and explosions, I think a threaded on charger plug would be more prone to twisting the socket that could cause a short circuit.  But that's on the charger side of the bmc. That wouldn't cause a short of the li-ion battery pack which can be catastrophic.

I tried this unbranded hoverboard out for the first time despite the battery being very low and the alarm chiming.  It works so it's worth getting a charger for.   My plan was to tear it apart and use the guts to make an electric 2 wheel bicycle that I can handle safely.

looking on line, I see many chargers. Some state "for lead-acid" in the specs but I think the sellers are more clueless than me.

 

 

[Chriull]

1 hour ago, rickpaulos said:

I took the covers off for photos.  36v pack with 18650 cells.  no mention of chemistry but I'm sure they are li-ion.  The 3 pin connector has 2 reds on one pin and 2 blacks on another pin and the 3rd pin is vacant.  I would think the bcm (battery control module) would regulate charging so the charger is just a dumb ac to dc converter.

No. If the hoverboards work like BMS (?bcm?) of EUCs the charger has to be a CC/CV charger for li ion. BMS (BCM) normally only check single cell (group) over and undervoltage.

The 36V standard voltage of your pack should state the nominal voltage. For Li Ion that's ~3.6V per cell. So with 10 cells in series in this pack (10*3.6V=36V) and a maximum charge voltage of 4.2V for "normal" and mostly used 18650 Li Ion cells this shoudl give 42V maximum charge voltage.

The capacity value of 4400mAh is a bit strange? I don't know of 18650 cells with this capacity - normal max capacity is ~3500-3600mAh. So there should be 2 cells of 2200mAh in parallel? So a 10s2p configuration - making 20 cells in this pack!?

With many Li Ion cells 0.5 C is specified from the manufacturer as max charging current - making 2.2A maximum charge current in your case. So some "normal" 1-1.5A charger should work?

1 hour ago, rickpaulos said:

I tried this unbranded hoverboard out for the first time despite the battery being very low and the alarm chiming.  It works so it's worth getting a charger for. 

Could still be that the li ion cells are misbalanced. Happens often with "weak batteries". On notices this if they do not charge to full voltage (~42V) anymore - then they could start to get dangerous.

1 hour ago, rickpaulos said:

  My plan was to tear it apart and use the guts to make an electric 2 wheel bicycle that I can handle safely.

looking on line, I see many chargers. Some state "for lead-acid" in the specs but I think the sellers are more clueless than me.

Lead acid have afaik a not too different charge characteristic from li ion but are definitely not usable ...

The guesses above should give you the needed specification for your li ion charger (with some 9x% probability). Many of these Li Ion chargers are named with something like "for 36V Li Ion battery" and mention of the 42V (max charge voltage). Somtimes the 10s/10 serie/10 cells in serie... are mentioned too.

There are masses of these with up to 2A.

You just need the right plug with the right pin out... Some BMS have reverse polarity protection, some don't... So you should check the right voltage on the right pins before connecting.

 

 

[alcatraz]

I've wondered myself what the difference would be to charge to 85v vs 84v with a weak charger (same amperage). If the BMS cuts it off at 84v anyway, is there a difference?

Batteries out of China are 99% the 4.2v kind. Hoverboard packs are known to be of questionable build quality so please be careful. What's been done is use mixed used cells. A simple/cheap bms can't balance mixed cells of different condition. They could also discharge very unevenly which means some cells could go outside the normal range 4.2-2.5v at sometime during the charge/discharge cycle. Also remember that when loading the pack you get voltage sag so even if you meausure 3.5v on three groups at home, another group could be at 2V when you accelerate etc.

It's no problem to use the pack for thousands of cycles once you know everything is ok. If it charges extremely slow between 90-100% that is a bad sign. Also look for physical damage, moisture or corrosion.

If the bms is completely unreliable and doesn't cut off charging at 4.2v (whichis hard to diagnose, best to assume is the case with an old inexpesive pack) then best is to measure the cell groups. Cut off the heatshrink and measure the pack, then put new heatshrink on. Only then you can be sure. If you want to continue to check the condition then solder on balance leads so you can probe the pack later. You will be thankful for doing it 1+ years later.