Lithium bike battery charging

tushingham2

Pedelecer
May 9, 2020
33
1
Lithium 36v ebike battery I noice some have a label attached charge battery with battery switched on. Is this important and better for the battery and is it best to charge when return from a short ride or let it run right down. Interesting to see different views

tushingham2
 

Benjahmin

Esteemed Pedelecer
Nov 10, 2014
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This subject has been covered ad nauseum, and generally ends up in some sort of bun fight.
If your battery needs the switch to be on to charge, then do so, otherwise turn it off as the bms will consume power when not in use.
Charge it- use it. Don't leave it fully charged without use for extended periods. Best to use straight after a charge. Where possible always charge to full (to allow cell balancing), though occaisional charge to less than full will not harm. Lithium batteries do not mind partial charges, that's to say a charge to full from partially used, in fact it's likely better not to deep cycle them.
Do not store for long periods fully charged, best left around 50-80% in a cool place.
Charge at room temperature i.e. not in a freezing shed/garage.
There - that should get the controversy going nicely.
Enjoy your bike.
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
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Basildon
It just depends on how the battery is wired. Some are completely isolated when switched off, others only switch off the output, leaving the charge socket live. If your battery charges when switched off, that's how you should do it.
 

WheezyRider

Esteemed Pedelecer
Apr 20, 2020
367
144
Some BMS units have a common connection to the charger and the battery output (just 2 wires out of the BMS). So if the switch is in series with the output, it's impossible for it to charge unless switched on.

Have a look at this picture. There are just two wires coming out of the BMS. The switch is in series, so it has to be "on" for any power to go to the BMS.

36649
 

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WheezyRider

Esteemed Pedelecer
Apr 20, 2020
367
144
This subject has been covered ad nauseum, and generally ends up in some sort of bun fight.
If your battery needs the switch to be on to charge, then do so, otherwise turn it off as the bms will consume power when not in use.
Charge it- use it. Don't leave it fully charged without use for extended periods. Best to use straight after a charge. Where possible always charge to full (to allow cell balancing), though occaisional charge to less than full will not harm. Lithium batteries do not mind partial charges, that's to say a charge to full from partially used, in fact it's likely better not to deep cycle them.
Do not store for long periods fully charged, best left around 50-80% in a cool place.
Charge at room temperature i.e. not in a freezing shed/garage.
There - that should get the controversy going nicely.
Enjoy your bike.
I think that's the best summary you can get. The rest is just controversy and not worth wasting your time on.
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
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Basildon
Some BMS units have a common connection to the charger and the battery output (just 2 wires out of the BMS). So if the switch is in series with the output, it's impossible for it to charge unless switched on.

Have a look at this picture. There are just two wires coming out of the BMS. The switch is in series, so it has to be "on" for any power to go to the BMS.
Is the switch on the main power wire? It'll most likely burn if it is due to the inrush current into the controller's main capacitor/s. I think it's better to put a low power switch on the 12v supply to the mosfets to switch them off.
 

WheezyRider

Esteemed Pedelecer
Apr 20, 2020
367
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Is the switch on the main power wire? It'll most likely burn if it is due to the inrush current into the controller's main capacitor/s. I think it's better to put a low power switch on the 12v supply to the mosfets to switch them off.
Yes, it's a 30A switch on the main power out. I also don't switch it under load. It's mainly there so I can cut power without having to pull the connectors apart and for emergency isolation.

When connecting to the charger, I also don't like having it loaded before the connector is disconnected from the controller and then plugged into the charger. I can isolate the battery. Same when reconnecting to the controller after charge. If it is not isolated, there is a big spark when connecting back onto the controller.

Do you mean modifying the controller MOSFETs? There is an on/off on the throttle already.
 

Andy-Mat

Esteemed Pedelecer
Oct 26, 2018
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It just depends on how the battery is wired. Some are completely isolated when switched off, others only switch off the output, leaving the charge socket live. If your battery charges when switched off, that's how you should do it.
That sounds like a very good and plausible explanation for some bikes/ batteries needing to be "ON".
Though possibly not quite cool is there is a possibility of theft or similar, for the owner, maybe.....
It would be interesting for someone with such a battery label, to actually see if battery voltage is available at the charging circuit, with the key in the OFF position, and then removing the key!
There is always something new here to think about!
Andy
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
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Yes, it's a 30A switch on the main power out. I also don't switch it under load. It's mainly there so I can cut power without having to pull the connectors apart and for emergency isolation.

When connecting to the charger, I also don't like having it loaded before the connector is disconnected from the controller and then plugged into the charger. I can isolate the battery. Same when reconnecting to the controller after charge. If it is not isolated, there is a big spark when connecting back onto the controller.

Do you mean modifying the controller MOSFETs? There is an on/off on the throttle already.
The mosfets are switched when they get a 12v signal on the gate leg. That 12v is switched by a transistor that gets a 5v signal on its base from the cpu or other controlling circuit. Trace the source of the 12v, which is easy when the mosfets are switched on, then cut the track and put any switch you want on it. That will switch the mosfets off manually regardless of other conditions.

A normal switch on the output won't last very long, regardless of its rating. The problem is the inrush current is astronomically high, and it burns the contacts. Some switch designs are better than others. You'll probably be OK for now, but you'll never know when it might leave you stranded.

If you want to see the inrush current, disconnect the battery, leave it for a few minutes, switch it on and reconnect it to the controller. You'll get a snap sound and see a big spark. That's what happens inside the switch each time you switch on.

Another solution is to use two switches or a two stage switch with a resistor on stage one to pre-charge the capacitor before engaging the main switch. Have a look at this:
 

WheezyRider

Esteemed Pedelecer
Apr 20, 2020
367
144
The mosfets are switched when they get a 12v signal on the gate leg. That 12v is switched by a transistor that gets a 5v signal on its base from the cpu or other controlling circuit. Trace the source of the 12v, which is easy when the mosfets are switched on, then cut the track and put any switch you want on it. That will switch the mosfets off manually regardless of other conditions.

A normal switch on the output won't last very long, regardless of its rating. The problem is the inrush current is astronomically high, and it burns the contacts. Some switch designs are better than others. You'll probably be OK for now, but you'll never know when it might leave you stranded.

If you want to see the inrush current, disconnect the battery, leave it for a few minutes, switch it on and reconnect it to the controller. You'll get a snap sound and see a big spark. That's what happens inside the switch each time you switch on.

Another solution is to use two switches or a two stage switch with a resistor on stage one to pre-charge the capacitor before engaging the main switch. Have a look at this:
I see your point about inrush current, but I don't hear/see anything when switching the battery on after connecting the controller. It's certainly a lot better than pushing the connectors together with the battery switched on!

On my battery packs, it's probably not an ideal solution, but it essentially just replaces the key lock switch present on a lot of packs. My two Yose Power packs have/had these key lock switches and I really can't see these being 30A DC rated. One pack has issues with the switch and you have to be careful how you switch it on, or it won't work. The other pack had dodgy soldering around the main fuse and it stopped working . When I opened it up, the switch part of the key lock was not very substantial at all. Now that one has a 30A toggle switch and it has run trouble free for quite a few months.

I do like the ability to isolate the battery from everything just by flicking a switch. If a short happens somewhere, I want to be able to cut power - and fast. I don't want to be digging to find the connector.

There is also a 30A resettable trip in series with the switch, so hopefully this would kick in if things got serious and a 40A trip in the BMS.

I've seen battery isolators for cars, boats etc, but they are probably a lot bigger than what is needed.

I'll have a look at the double switch system you suggest. Maybe I can incorporate that into my next build.
 

WheezyRider

Esteemed Pedelecer
Apr 20, 2020
367
144
This is what the working Yose Power key lock switch I took out looks like, after not very extensive use.

The one I still have in the other pack is probably even worse as it is failing at times.




36654

36655
 

PP100

Pedelecer
Feb 28, 2020
135
72
I think that's the best summary you can get. The rest is just controversy and not worth wasting your time on.
Could this or some sort of summary be made a sticky for later easier referral - It won't stop all questions but it might help to reduce the basic newbie one (of which I include myself not long ago)
 
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