Battery Charging

[d8veh]

Many OEM bike suppliers advise you to plug the charger into the battery before switching the charger on at the wall. Does anybody know the basis to this instruction?

On all the batteries that I've tried that, you get a nasty spark when you connect, which I guess is capacitors in the charger getting inrush. You can see the damage it does to the jack socket in bottle batteries. In one case the damage was so bad that the jack-plug hooked the earth strip out when it was unplugged, which shorted out the charge socket completely and made big sparks.

If you switch on at the wall first, does the inrush to the capacitors damage the charger? Is that the reason they don't want you to do it that way round?

 

[dnmun]

no, the inrush to the charger is essentially a short circuit. that is why they include the Inrush Current Limiter ICL to slow the inrush of current and prevent the fuse from blowing.

you wanna have the charger turned on before connecting to the battery to prevent the spark from the battery charging up the output caps on the charger.

 

[dogman dan]

Idiots. there is an inrush limiter on the AC side, and there is not one on the DC side.

But,,, you won't blow the inrush limiter on a shoddy charger if you plug in DC first. So rather than provide a good charger... Facepalm.

 

[Ykick]

ICLs I’ve had fail appeared to be marginal ratings. I don't think capacitor spark had much to do with their failure.

Now I instruct friends/users to always power-up the charger 1st and then connect the pack. I believe this puts less stress on the ICL as things have a moment to wind-up to operating normal mode throughout the circuit.

Somebody with genuine knowledge please confirm but is it likely an ICL is under more stress powering up with a charge load connected?

I’ve decided so and haven’t had one fail ever since powering chargers before connecting the battery pack.

 

[dogman dan]

Best to power up through the ICL, I'd think. Have to confess to doing it randomly either way, myself. Trying to form a better habit.

 

[dnmun]

yep, i do it all the time even though i know better. my extension cord has burn marks all over the spades where i plug it in.

i doubt if there is a difference in inrush current if the pack is already plugged in.

the hit is to the pin contacts on the output of the charger because the rush of current from the battery into the output of the charger is still a buncha pop.

 

[Dave Sloan]

I tested the five different charger that I have and there is not enough current going back into the charger to run a cell phone = when the battery is plugged in first. My largest charger is 5 amps - so I can only assume these are high current - cheaply built chargers. Most of my chargers are over four years old and except for the fan needing replacement on one and the inrush of a lightning strike while camping blowing the little black AC protection (easily replaced) the battery should always be plugged in first = mine came with instructions to do so.

 

[dnmun]

you got incorrect instructions then.

 

[Racer_X]

Always power-up the charger 1st and then connect the pack.

I have damaged a few chargers by plugging the charger into the battery before switching the charger on at the wall.
I heard a POP and that was that one. It did not happen every time but after a few i decided to make it a rule to Always power-up the charger 1st and then connect the pack.
Now my BMSbattery Lipo Bulk chargers have been working for me wonderfully for several years and still going.

 

[dnmun]

it is so obvious that the charger should be powered up first that it always gives me pause when a seller of battery chargers sends out instructions telling the user to plug the battery into the charger first before powering it up.

that causes me to think that the seller really does not understand the product they are selling.

but of course i just did it too. my chargers are soldered to the BMS and B+ terminals so they are always connected to the chargers so every time i power up the chargers i get the full inrush current the ICLs will allow.

if the charger has the relay on the output or if it has the pchannel mosfet on the output then it does not matter but if you have the switch on the side of the kingpan next to the plug then turn on that switch first before connecting the battery. that powers up the back end.

 

[tmho]

Usually I will power up the charger and then plug the charger to the battery pack. But I have a battery pack and charger which do not allow me to do so. If I power up the charger first, then it will not charger the battery (the red light on the charger stays on and will not turn to green, green means charging). I need to connect the charger to the battery pack first, then the red light changes to green and the battery pack will be charging. Was the charger designed in such a way or just something wrong?

 

[dnmun]

open up your charger and show pictures of the inside in the back end if you want help answering that question.

 

[tmho]

open up your charger and show pictures of the inside in the back end if you want help answering that question.

Thanks for the reply. I am now out of town. Will show the photos of the inside of the charger when I return home next week.

 

[tmho]

open up your charger and show pictures of the inside in the back end if you want help answering that question.

Thanks for the reply. I am now out of town. Will show the photos of the inside of the charger when I return home next week.

Attached please find the photos of the charger.





Attached please also find the photos of the BMS. Will the BMS makes it need to plug the charger to the battery pack first?
Also, it seems to me that there is no balancing function during charging. Could someone please advise if there should be balancing function for this BMS?

 

[dnmun]

it looks like the shunt resistors are on the left side of your second picture. R22 up to R32 and that is an 8S BMS.

what kind of battery do you have and can you measure the voltage on the output of the charger?

 

[Nobuo]

Taking a look at at the board pictures I think it's really a 10s BMS, those ones that need B+ main battery lead to be connected on the PCB, along with B- main battery lead and those 9 balancing wires, in order to take all the voltage reads.

I'm almost sure it is also a balancing board, doing the discharging through the resistors on the PCB side where discharging mosfet's are.

 

[tmho]

My battery pack is 10s4p 18650 lithium ion battery pack.
The output of the charger is 37.2V. But when I hook up the output connectors of the charger to the multimeter first and then plug into the wall, I can see that the multimeter shows 42.5V for about half a second and then changes to 37.2V.
For the balancing, may be the process is too slow that I did not have a chance of noticing it, or may be something wrong.

 

[dnmun]

if your battery is only charged up to 37.2V then that is what the output of the charger will read when it is attached to the battery. i noticed there is a high side mosfet on the hi voltage from the battery too.

if your charger will not put out the 42.2V continuously while disconnected from the battery then there is something going on with the charger to drop the output voltage.

it is 10S, i can see one of the resistors has 101 so it is 100 ohm shunt balance resistor. 42mA balancing current.

 

[tmho]

The battery can be charged more than 37.2V only if I connect the charger to the battery first. That is so strange and why I post it here.

 

[999zip999]

I have put together many different ebikes. Pedego, haibike, eflow, izip, emotion. Most of them that have instructions say to plug the battery first. But some don't say anything ? I charge my 36v A123 on a cheap 2a pedego charger with plugged in the wall first. Could be doing it wrong ? What does Ping say with his chargers ?
I think different chargers are set up differently.

 

[dnmun]

The battery can be charged more than 37.2V only if I connect the charger to the battery first. That is so strange and why I post it here.

there is more to it than what appears to you i bet. can you find another 42V charger to use on your battery with this BMS?

 

[tmho]

The battery can be charged more than 37.2V only if I connect the charger to the battery first. That is so strange and why I post it here.

there is more to it than what appears to you i bet. can you find another 42V charger to use on your battery with this BMS?

Now I only have that 42V charger. Will try that later when I have another 42V charger.

 

[999zip999]

I can't find it, but doesn't Ping plug charger to wall first ?

 

[999zip999]

So your battery will charge to 42 volts ? What is your final battery voltage ?

 

[dnmun]

your BMS is unusual in that there is the full battery voltage coming onto the BMS. it may be that the B+ provides the circuit current for the digital ICs there that control the charging. but it should charge to 42.2V if you are able to push that much voltage out of the charger.