Some questions re LiPo, bulk charging and BMS

Batteries, Chargers, and Battery Management Systems.
Post Reply
kiwipete   100 mW

100 mW
Posts: 45
Joined: Nov 13 2013 9:40pm

Some questions re LiPo, bulk charging and BMS

Post by kiwipete » Jan 08 2014 9:54pm

I have bought a standard MAC kit from Paul (cell_mann) and I’m really happy with it (not in the least as a result of the good info and help from people on this forum).

My battery is a 12S Lipo pack (3 x turnigy 4s 5000mah hardcase bricks) and I am charging it with a 106B Icharger which also works fine.

I have found though, that I like riding the bike much better than charging it: I have been balance charging the three bricks individually, so that takes a fair bit of time and attention.
So I’d like to move over to bulk charging and maybe once a week do a parallel balance charge and check the individual cell voltages.

A few days ago I came across a post from ‘dogman’ advocating a 14S pack (by adding a 2S to my existing ones) and then using a charger like the 58.8V / 5A charger from EM3EV for bulk charging. I quite like this idea, but have a couple of questions:

- I have the standard 6 FET, 25A controller from EM3EV which supposedly can handle up to 60V. Will running it at close to 60V regularly shorten its lifespan?

- The next step then would be to use a BMS and make my charging life easier again. I could either get one from EM3EV or from Bestekpower. Which model from Bestekpower is the best for this setup? (also price wise).

- If I then at a later stage want to increase my capacity / range from 5Ah to 10Ah ( by buying another 3 x 4S bricks and another 2S) how does it work with the BMS then? Do I have to buy another BMS for the new batteries and run everything in parallel?

dnmun   100 GW

100 GW
Posts: 16190
Joined: Jun 09 2008 1:32pm
Location: portland, or and loveland, co

Re: Some questions re LiPo, bulk charging and BMS

Post by dnmun » Jan 08 2014 10:49pm

you can go up to 16S on the Bestechpower BMSs and only use the first 12S channels initially and if you wanna go to 15S or 16S later you can just add them in series. the D166 is good for 40A continuous and 80A surges. D167 is 35A and 70A surges. i have been selling them here in the states for $45. if you are in the states lemme know because i was gonna order some more about a month ago for some others too but got sidetracked.

lipo is good about remaining balanced after it is initially balanced, unlike the lifepo4. but the BMS will balance the pack just as well too. a balance charger is just the same as bulk charger and BMS together.

the value in using a BMS is the short circuit protection on the output and protection against over discharge if the battery is left connected to the controller. you do not get either with a balance charger.

User avatar
dogman dan   100 GW

100 GW
Posts: 35627
Joined: May 17 2008 12:53pm
Location: Las Cruces New Mexico USA

Re: Some questions re LiPo, bulk charging and BMS

Post by dogman dan » Jan 09 2014 8:14am

I don't recommend naked bulk charging as the best way. But I'm doing it now, because it's cheap. To be completely clear, all my bulk charging is taking place in a fireplace. I do it in a place I would deliberately build a fire.

I get away with it by treating my lico very gently. I do run a 5 ah pack on the dirt bike, but the typical ride barely takes it to 3.8v. It's just a quick lap to run the dogs, about 4 miles total. On the cargo bike, I run a 15 ah pack so the discharge rate is light, and I tend to stop most discharges at about 3.6v or less.

So I very rarely unbalance the pack.

I DO NOT bulk charge naked to 4.2v. I stop at 4.15v, giving myself an extra .05v of safety margin. I do check the cells fairly often, but haven't had to balance more than once every 2-3 months.

I NEED to get off my ass, and get some of those bms's. But I'm broke, and need a few more ah of battery more. So that's what I got for Christmas this year, another 5 ah of 14s.

If you want to use the bms on a 10 ah pack, it's pretty simple. Parallel the packs into 10 ah packs, at both the main wires and the balance plug. Then install the bms to the now paralleled ,10 ah balance plugs.

I would stick to no more than 14s with that controller. It's designed for that much, so it's not going to make it pop because you run 58v fully charged. You will drop to 54v pretty quick too.

User avatar
Ykick   100 GW

100 GW
Posts: 5558
Joined: Nov 26 2009 6:10pm
Location: San Diego, California

Re: Some questions re LiPo, bulk charging and BMS

Post by Ykick » Jan 09 2014 8:41am

I think if you're gonna bulk charge with or without a BMS you will be better off learning about power supplies and how to achieve/adjust voltage ranges. Series wiring is your friend.

Paul's looking into modding one of his multi-voltage 4A chargers for me to use 16S RC Lipo but I haven't heard back yet if that's a go or no go?

For 12S RC Lipo a single 48V MW will do fine operating in the 50V range.

16S things get a bit more complicated - that's why I reached out Paul about a mod for his 4A alloy charger and in the meantime added a 12V MW in series with my old 48V MW to hit 66.4V for naked top charge of 16S RC Lipo.

If I do ever add a BMS I should be able to crank up voltage enough to allow the BMS to do it's thing and still use the same charging gear.

Naked charging can be volatile and only pursued if you're basically hovering over it and/or doing it in a relative non-flammable area.
Talent must not be wasted.... Those who have talent must hug it, embrace it, nurture it and share it lest it be taken away from you as fast as it was loaned to you.

- Frank Sinatra

User avatar
wesnewell   100 GW

100 GW
Posts: 7170
Joined: Jan 31 2011 6:25pm
Location: Wylie, TX, USA

Re: Some questions re LiPo, bulk charging and BMS

Post by wesnewell » Jan 09 2014 2:52pm

For my 24s pack, I prefer to use a balance charger. It only take a few seconds to to split it in half electrically and charge the whole pack as a 12s pack using a 12s balance charger. Takes ~2 hours to fully charge my 888wh pack. And it's just as safe, if not more so, than using a bms and just a little less convenient. Although now that I'll probably always use a 24s lipo pack, a 24s bms would make charging a little easier. But that's really the only adnatge to using a bms. You're just fooling yourself if you think it will do much more for you than give you protection from over charging.
My most feared BMS disaster scenario;
Cuts out on you because of low cell group while crossing busy intersection. Could be deadly, and the main reason I don't use one. Screw the battery protection. Won't do me much good in the hospital or morgue.
Need Advice? ... =3&t=66302
Mongoose 26" Ledge 2.1 mtb bike $99, 48V 1000W rear hub kit $200, Hua Tong 72V 40A controller $35, 10ah 24s lipo $217=~43mph, range=45 miles @ 20mph. 25K miles and still going strong.
Huffy Fortress 3.0 with MXUS 3000 4T motor, 24s lipo, 96V 60A controller. Total cost with extras <$700. Top speed ~50mph
My videos ... _G2wQhptMg

User avatar
dogman dan   100 GW

100 GW
Posts: 35627
Joined: May 17 2008 12:53pm
Location: Las Cruces New Mexico USA

Re: Some questions re LiPo, bulk charging and BMS

Post by dogman dan » Jan 10 2014 7:20am

Been there, done that, but didn't get hit. But usually you do know it's coming, a bms shutoff, if you pay any attention at all to how the bike is running.

I would like to run 12s, if I had a really good 12s RC charger. Like the ones that charge each cell separately.

I have been very happy charging 14s with the three voltage EM3ev 5 amps charger. It has pots inside you can diddle with. I reset mine to charge to 4.15 max rather than 4.2, and the other settings are 4.1 and something in the middle, 3.8 or whatever. I don't recall exactly, I seldom use the storage charge setting.

Since 99% of the time, I was not selecting balance charge with my RC charger, I don't see much difference. Bulk charge is bulk charge, if you don't do the actual balance charge. Even if you have an RC charger, bulk charge is the same thing. I can carry the bulk chargers easy, for longer trips. That's the main reason I made the change to using them, I still have this fantasy of a 200-2000 mile trip.

Key thing is, both my RC chargers and my bulk chargers shut off the current at the finish. I verified this with a wattmeter, the EM3ev charger current does go to zero when the light is green. Volts still there, but current is 0. So if I am not right there to unplug, it's not overcharging the pack.

For ALL bulk charging, you obviously have to be vigilant that you have no bad cells in the pack, that can overcharge. I do watch that, by checking for high cells at the balance taps as the charge is nearing the finish. I want to detect a low capacity cell early, before the fire.

My experience so far, is that once you get to cycle 30 or so, and have not had a bad quality cell, you are good for many more cycles with no wonky cells. Bad cells fail soon, so weed them out when the pack is new. Watch a new pack like a hawk.

And I'll get in the habit of saying this over and over,

Don't bulk charge cheap hobby RC lico in a place you wouldn't build a campfire.

Post Reply