integrating single cell chargers into BMS circuit.

[BiGH]

Hey everyone.

I'm looking at integrating a single cell charger solution into my old YESA pack. (i'm still waiting on getting my headway pack back after the BMS broke on that )

Basically at the bms there are a bunch of wires running to each of the individual cells. can these be left attached while i charge the cells?

Also what connectors did everyone use for their single cell chargers. I have 72v on the bike - which would mean quite a few chargers in parallel (12 for each 36v pack)

 

[Kurt]

I have been thinking about single cell chargers myself. I think I am just that kind of person coming from a mechanical background that likes to see things working.With electronics that isn't very often posable without a complex array of instruments and probing every part of the bms you just have to trust all the little parts on the bms are doing what they were designed to do.

My ideal charging station for my 36v 20ah headway pack would be 12 single cell chargers one charger for each two parallel cells. A long 12 or two 6 socket power outlet boards and 12 low cost multimeter's you know the little simple $5 kind.

Make up a board for the garage wall with it all on there. I don't think you could go wrong. I would know each cell is getting its 3.7v and I could check that at a glance of the multimeter's.

Problem is the only single cell chargers I have seen are $20 Aust so it starts to add up. $240 for the chargers then say $60 for the multimeter's then another $30 for plugs, wire, solder power board . That's a $330 charging station just for a 36v 20ah battery. It's almost 1/2 the battery cost. Even so I still like the idea.

I you could uses the original bms sensing wires to charge from but I would prefer to solder on my own wires and plugs as the standard headway bms wires ain't that flash.

Kurt

 

[BiGH]

well my idea is if u made a set of ports then you could just plug in one charger to multiple ports - while its not a on its own charging solution, it would speed re-balancing.

and then as funds permitted you could get more.

ports though - not sure on this.

 

[liveforphysics]

You guys might want to look at pro level RC battery chargers. They display the voltage of every cell for you while charging. They charge fast. They can be programmed to cycle your packs for you, and calculate the resistance of each cell, and calculate the capacity of the pack from X voltage to X voltage. You set them up for your battery, then just plug it in whenever you want to charge, and it displays the voltage of every cell for you while it's charging. Most all of them can be set for LiFePO4 or LiIon, or even lead acid or NiMH or NiCad. They weigh about 1-2lbs, fit in your palm, and you only need 1 of them for every string of 10-12cells (some models to 12s, some only 10s). They will also shut down if they sense anything funny going on with even a single cell in the pack, and then alarm to tell you which cell in the string they aren't liking. They use super compact little JST plugs to connect to the charger, so the bundle of wires mess is minimized. They run off car battery DC voltage, which is a both a good thing and a bad thing. The good thing being you can easily find a mobile charging station from any car that stops to help. The bad thing being you need to also buy a 12-16vdc power supply to run them off your household voltage. Fortunately, these are very cheap, small, and compact these days, so it's not nearly the issue it used to be.

Best Wishes,
-Luke

 

[fechter]

I think it would work fine to use single cell chargers with a Ping BMS. You could just attach the chargers directly to the battery connections and bypass the BMS for charging. For discharging, the BMS chould still work to protect against low voltage.

 

[oofnik]

You guys might want to look at pro level RC battery chargers. They display the voltage of every cell for you while charging.
Best Wishes,
-Luke

Yep. Here's a G.T. Power 200W 6S charger working on my (horribly unbalanced) Headway pack.
I've got it set up so it's easy to switch from 12s1p on the bike to 6s2p on the charger.


But back to the topic... Voltphreaks sells single cell 3.7v 2A chargers at $10/ea for 10. For a larger quantity, contact Tony and he may be able to help you out.

 

[swbluto]

Now that I have two broken Ping BMS's, I'm swearing off Ping's BMSs and I'm trying other solutions(I also need to reduce the series count in my pack as I now have less viable cells to work with, so the BMS wouldn't be particular effectively since it's designed for 16 cell groups) that I know that I would be able to diagnose, fix and be relatively reliable. To that end, I think the Fuse+LVC board+Single Cell chargers would work absolutely excellently! And it seems like it can be pretty cheap DIY.

I'm planning on building an LVC based on a microcontroller I have+resistive dividers+16analog-mux which seems like it runs to around $20 in construction costs in a DIY fashion(I only have to supply the mux, so it's only less than 5 dollars extra for me). For the single cell chargers, look for schematics for SLA chargers - Some of the available designs floating online have an alterable output high voltage and current control(meaning you can adapt them to lifepo4 quite readily), and they also look pretty cheap. Assuming you have a 6-10V source available at relatively high amp capability(Shouldn't be hard to devise but I just haven't yet; I'm thinking a Flyback converter would be best for cheapness? I may as just well go for the easiest route and build whatever seems best for a DIY Power Supply online), you can actually build each single cell charger for less than $3(Not including the board) in materials! Of course, that's limited to a 2A charging rate and more amps means more money, but I think it could be cheap for more amps although the solutions I've seen seem to involve expensive chips! There's also another source I've seen on the boards(I think it was from voltphreaks) that you can get 2A plug-into-the-wall Lifepo4 single cell chargers for $10 each if you buy 10 or more. Might be a convenient and relatively cheap solution.

Also, there's sources on the board for conventional blade-style high-amp fuses. All in all, it seems a robust, adaptable charging+LVC+fuse system seems like it should cost less than $60 out-of-pocket but I think it should cost me less than 45ish dollars given I have many of the materials on hand. Also, the fuse is going to be "slow acting" instead of a BMS's "Cut out immediately if it goes over x-amps" modus operandi.

 

[swbluto]

They use super compact little JST plugs to connect to the charger, so the bundle of wires mess is minimized.

Are these JST plugs capable of being configured so that you don't have to individually plug in each connector? I mean, can you easily create "blocks" of JST plugs like you can with anderson powerpoles and just connect/disconnect all the plugs in one motion?

 

[swbluto]

You guys might want to look at pro level RC battery chargers. They display the voltage of every cell for you while charging.
Best Wishes,
-Luke

Yep. Here's a G.T. Power 200W 6S charger working on my (horribly unbalanced) Headway pack.
I've got it set up so it's easy to switch from 12s1p on the bike to 6s2p on the charger.

That's incredibly smart. I didn't think of parallel switching cells to minimize the investment in the balancer, I was just dreading the idea of buying multiple balancers.

What power supply do you have to power the charger?

I'm getting the idea the conventional practice with RC battery balancers/charger is to have a low volt, high-amp PS to supply power to a balancer. Is that right? That sounds roughly similar to the idea I was thinking of implementing. Do you have an idea of what it would roughly cost for the balancer to get a charging current of 4 amps per each balancer lead on a 6s balancer? 2 amps on a 12s balancer? Also, how much did the power supply cost and where/how did you find it?



Hmmmm... *thinking*... I think a PC power supply could be used for the charger. Not particularly compact or light and I may have to add a few capacitors for output filtering, but it's good for an at-home solution and it seems any effective portable/light solutions are going to cost some extra dough.

 

[oofnik]

I got the charger and power supply from hobbycity.com. The power supply is 16A / 14 v and holds its voltage well until it cuts out. The charger has an integrated boost converter to be able to charge at higher voltages.

When charging the pack in 6s2p, it takes slightly over four hours to fully charge and balance from completely empty. The charger is completely microprocessor controlled and is very slick. The total was about $110.

The only problem is that I'd really like to have cell level protection on the bike. I'm going to be ordering a 400W charger and a BMS from eCityPower.com later today and I will compare the charging times for both setups.

 

[liveforphysics]

I personally like this one better than hobby city's biggest 12vdc power supply. When you add in shipping, its only a tad more expensive. The chargers love to get 14vdc input, and if you crank the adjustment pot all the way on this guy, he just makes 14vdc.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWNX:IT&item=370180428901

For doing groups of 10s cells, this charger rocks:
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=6609

for doing 12s, the megapower works, but only 60mA of balancing current, so it takes forever if your pack gets way out of wack. The hyperion 12s I think does 500mA balancing, but it also costs twice as much.

 

[swbluto]

I'm liking the eBay power supply. I just don't know how much it weighs, though, as I see 1 figure around 1 kg and then another over 10 kg and it'd be nice to have something I could tote around(opportunity charging and all ).

 

[liveforphysics]

It's small and light, and the fan moves a lot of air. I haven't weighed mine, but I would say under 2lbs. That badass 10s charger feels like 1lbs when you lift it, and even pumping 10amps, it's fan keeps it nice and cool. Very compact and powerful stuff. This stuff is so far ahead of ping chargers and SLA chargers, it really cant even be compared.

 

[oofnik]

This stuff is so far ahead of ping chargers and SLA chargers, it really cant even be compared.

Agreed! Ebikes need to get out of the electronic stone age!

I found that ebay PSU shortly after I bought the HobbyCity one. I was kind of wary about the quality though. Sounds like it's holding up well for you. I might order one to replace mine as it cuts out when I max out the charger. I can't charge 6s over 8.0 amps although the charger is capable of 10 amps. Maybe I can disable the overcurrent protection...

Well I just ordered a 9 amp charger and an 80 amp BMS from eCityPower.com, so I might wait on that.

 

[liveforphysics]

With most hobby chargers, when the power drops below 12.5v, they start cutting back the current they charge with. That's the beauty of that 29amp supply, you crank its resting voltage up to 14vdc, then when the charger is drawing it's peak current, the voltage hangs around 13vdc or so, and the charger keeps peak charge current high.

Years ago, i always used a computer power supply to charge. It worked fine, but the charger would never do the full rated current like it did when i used the car battery from a running car. That's when i figured out that they cut the current back for voltages below 12.5vdc.

This same guy sells a pretty badass setup with a pair of 60amp 7VDC chargers, made to be connected in series to make a 14vdc 60amp supply. I think it was like $90-100bucks shipped.

 

[swbluto]

Coincidentally, I was looking at the 7 volt PSUs. The chip I'm planning on using(L200 for the curious) seems to need an input voltage somewhere between 2.5-4 volts higher than the output, and a 7V supply adjustable between 6-9VDC sounds like a good way to go for 3.7V charging while minimizing heat dissipation. And plenty of amps available, too. But, for now, I think I'm going to test out the 12VDC on my dead computer's PSU and try that before buying another PSU. Even though it has a max current draw of 24 amps, I think I'm willing to wait 4-6 hours as I've never seemed to have needed a shorter charging time. It's not like I come home just to charge up for the next leg of the day's journey(Back when I had lead, though.... mmmm, fond memories).

 

[liveforphysics]

If you want power at lower voltages, I have some high amperage 3vdc and 5vdc power supplies that I will just give you if I can find them in my storage unit. They were used for driving laser diodes back when I was way too into that...

Or, you can just buy your own for cheap!

http://cgi.ebay.com/Astec-VS3-C2-A2-01-Regulated-DC-Power-Supply-5-5VDC_W0QQitemZ370182260923QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item370182260923&_trksid=p3286.c0.m14&_trkparms=72%3A1205%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318%7C301%3A0%7C293%3A1%7C294%3A50

I've bought 2 x 42vdc voltage supplies of the same brand from this lady, and they are fantastic. Serious professional quality stuff, that she is selling for nickles on the dollar. The pro line of Astec is the same quality of stuff they use in MRI machines.

 

[swbluto]

That sounds like a good avenue to explore. Unfortunately, my ideas got the desperate professional attention they deserved and were shot down like tethered blimps so it's beginning to seem like balancers are among the best way to go.

Hmmmm.... but let's see, I believe DoctorBass had a resource for cheap single-cell chargers for cheap-fast charging back in the day, although I'm not sure if that resource is still around. I'll try finding his thread(s).