BalacingBus (no BMS), Positive feedback
I had been using a Lifepo4 pack with no BMS, just occasional cell monitoring and manual topping up if required.
All was ok, but I want to report that this new method with the Self BalancingBus is easier.
I took all the batteries and wired them to a block of Powerplugs.
These are connected to a SeriesBus for charging and driving
and I connect the BalancingBus when Im not using the scooter. This has all the +ves and -ves connected in parallel and levels the cells
I can feedback that its keeping the cells in the pack at similar voltage without any other intervention - Dont know why I didnt think of it before!
Nice idea, simple when there are only a few cells.
You could also achieve even better balancing if yo use a charger designed for a single cell, but charge with the balancing bus in place. The balancing bus could be the charger connector.
Yes, good point Mik.
I have tried parallel charging with a single cell charger, however it took ages!
The problem is you really need a 4v charger that can do > 40amps if charging a dozen or more cells - (The biggest single cell charger I have can only put out 5amps!)
If anyone knows where its possible buy a high current single cell charger I would be grateful if they could post details
Also Mik you are right again about the block getting bulky when there are more cells.
Im thinking of trying to make a new type of 16 to 16 connector, maybe using magnets to line up flat contact on the face of a block, rather than clicking things together. Ive just ordered some Dental Acrylic to do some experiments mounting contact discs in a resin block... watch this space!
a powersupply like this:
Thanks -Would be good - but its expensive.
The other thing with using bench chargers is they need monitoring, as they dont have any detection to cut off charging when Batts reach the required voltage.
Thats why Im still having to series charge, the chargers dont need to do many amps and theyre cheap on Ebay!!
when connecting in parallel you should not use a simple wire but put some current limiting resistor
If you have a cell a little lower than others this cell when you do the parallel connection get brutally charged from the other cells without a current limit and can be damaged.
Paralleling is a good strategy to balance a small pack and save the money of BMS but you still need to do it in a proper way
For example if you do a parallel between a cell charged at 3.3 and another charged to 3.4 you can have current up to 10A-20A flowing between the batteries
One option is to do a balance before and after charging so you can reduce the imbalance.
In your case paralleling is very easy , you can consider paralleling every time the battery is not in use.
Hi Athlon, thanks for your comments but on the readings so far its fine, No resistor needed, when I use BalancingBus everytime my max difference in cells at start is 3.63V and 3.55V (pack average is 3.59v)
The internal resistance of the batts is 10miliohms plus another 10 in the wires so 0.02 ohms total Resistance
I=V/R gives max current as 0.04/0.02 = 2amps
The 10amphr cells can take a 1C charge so this is well within limits.
A resistor would delay the time the balancing takes.
The only negative thing about this way of balancing is that for my 36v system there are 24Andersons plugs clipped together in each the connector. Ive been doing some experiments at making a new type of 24 to 24 connector (out of Resin + Magnets) but its all looking very DIY at the moment lol!
Hi Colin, although I don't have any problems with batteries out of balance so far, I am considering applying your solution for the future. Indeed, you even don't have to charge the batteries in parallel configuration: just a balancing period ofter serial charging will do the job. However I have a few practical questions: while driving, the current can be high, the current during balancing is limited.
I have 4 12V 38 AH SLA-gel Greensaver batteries. My HUB motor has 1500W. Did you use the 15A, 30A or the 45A contacts? I am planning to use the 45A for connections to the batteries and for the SerieBus and 15A for the BalancingBus. The wires for the SerieBus seem a little thin, what is s their Gauge. What current will they be able to take?
And one last question: is it easy to plugg and unplugg the connectors, it needs to be done almost every day? Do they not get unplugged while driving?
Hi, very good question, yes I used the 45amp Anderson Powerplugs for everything, I didnt know the 15amp ones would match with the 45s if you used smaller ones for the BalancingBus but I just looked it up on powerwerx.com and it says the housings are the same so thats interesting!
Oh and yes I should have used a bit thicker wire really but my hubs only 250watts so its ok.
But I did have real problem soldering and clipping the inner metal section into the Powerplug when I first got them, I had to ask Mark for tips on how to do it because it wasnt as easy as I hoped, and Im not the worlds best solderer!
I like the way they clip together in a block but Id still like a better block connector if there was anything around because when you get up to 16Lifepo cells the 32block of Andersons is clunky!
If anyone comes up with a really good connector for 16 pairs of wires to another 16 pairs of wires Id be very interested.
With SLAs the balancing bus is easier because youre only talking 8 contacts. And No the SeriesBus never disconnects when riding, the powerplugs take a reasonable pull to get them apart
I would like to follow your method for my 16cell 48v 12a headway battery pack. I'm guessing that i need 16 pair of andersons for series connection...running and charging. 16 pairs in paralell for balancing.
Would this be correct? Any advice or recomendations would be truely appreciated...
My 1st bms has cost me 6 dead cells....I'm not going the game this way any more.....
Yep, Some of those BMS units kill cells.
You are correct in that you need 16pairs of connectors - its a bit much really. Also we concluded that Parallel charging is better than just Balancing after and its hard to find a single cell Lifepo4 charger that can deliver high amps.
So the working compromise was to group the Lifepo4 cells into strings of 4. and have 4 blocks of these charging with a Parallel Bus, (and running with a SeriesBus)
Advantages are =
1) you only need 8 connectors,
2) Can charge the 4 strings in Parallel with cheap standard 12v car charger than can give decent amps
disadvantage is that you have to check individual voltages in each string of 4 now and again. BUT using the standard 12v charger it takes each cell to about 3.5v which gives a comfortable amount of margin for error so its ok to monitor them less often!
Also great thing about Headyway cylindrical cells is you can connect them in a line with 6mm Diameter screws (saw the heads off) then they screw in end to end. Put 2 one way then 2 back the other direction and you have a neat 12v unit with no wires, and the +ve and -ve terminals up the same end!
Thank you for your quick reply.....I'm forced to stick to a set battery arrangment....I custom made my bicycle to take the battery pack in this particular way, I hope that the photo's make this clear....I can purchase 5 pair of anderson's for $7.00 aussie...I have emailed the supplier to see if this price still stands...I am thinking that with a block of 16 pairs, I might be able to fiberglass the connectors into a ridgid block eg 150mm long by 25mm wide....If this is the compromise that I have to make to follow your wonderful method,then so be it.
I just recieved an email from the anderson supplier....I've ordered 50 pairs @ $65.00 aussie delivered to my front door...I ordered the large number because I will make mistakes and I would like some spairs at the end of the day.Now I've just got to get the crimper...
Im really interested to see what you come up with, As I said I found 32 connections too much so settled for parallel charging 4 strips of 4, but hey it sounds like youve ordered enough connectors to do loads of experiments with Lol!
That block which holds your cells - did you make that? If so how?
At the moment what do you use to connect the cells in series? Do you have the cells alternating directions so its easier to connect the cells in series?
Thank you for the reply....yes,I did make the battery housing....I used 40mm dia pvc tube from the local plumbing supplier,I found that there was 2 types available...a loose fitting and a snug fitting, there appears to be a slight difference between manufacturers pvc tubes.I went for the snug fitting sized tube.
I contact glued the 16 tubes into the shape...I filled the outside valley's of tube pack with expanding foam...sanded the foam back to the level of the tubes...then fiberglassed the outside of pack with course matting....pack width is 83mm...narrow and strong.
in to the bottom end of each tube I gluded a 5mm wide pvc ring..this acted as a stop for each cell,I could now drop each cell into it's tube...I made a fiberglass strip 2mm thick, same length and width as pack with 16-20mm holes,this was gluded to the bottom of pack...with this in place the end of cells terminal was at the same level as the pack.
The pack is connected in series with terminal 1-neg at rear end of pack,right hand side +,-,+,-,to cell 8,front of pack...across to cell 9,left hand side now +,-,+,- down to cell 16-pos at rear end of pack.cells 1 and 16 are output and input terminals.I use the flat metal busbars that come with the headway cells.I had to elogate each hole 3mm to fit....GEE I hope this makes sense....
Do you have any photo's of your battery pack all wired up and connectors in place? Please excuse me but my little brain is having trouble seeing the full picture...Is your pack wired up in series to the permanent block and stays put, for running and series charging?.... and the removable block is in paralell for balancing and/or paralell charging?...please set me straight if I have this wrong
Ill take some pics. I now have them as 12v units (4 cells alternating down up down up connected with screws / bars) and each set goes to a pair of connectors.
These are then connected in series with the connectors to the motor, and parallel to the charger (12v)
By the way do u need any extra Headway cylindricals if a few of urs have gone bad? Ive got a few spare ones I would be happy to send u?
Thank you for the kind offer...I actualy ordered 4 more cells last night...hopefully I'll have them in a fortnight...I'll use 3 and have 1 spare....By following your bms free method I hope that I can get a good run out of my batteries this time....Do you run a low voltage alarm or something of that nature?...Or do you know the limits of your pack through experience?
sure, well Ive got those cells if u ever need them. I never run my pack right down so not had a problem.
Personally I think these BMS systems sometimes fry the cells by charging them too high. Ive found a 12v charger over 4 cells (or even 4 strings of 4 cells) charges them to a good level.
When arranging the cells into groups of 4 I do mine 2 down 2 up. I then just pile up sets of these in my battery box.
But as you have your proper holder it may be better for you to do 1 down 1up 1down and 1up if you know what I mean.
I use screws with heads cut off to connect the two in line, and just a piece of copper strip screwed in to connect the pairs.
What do u have in your current arrangement?
This photo shows one of the sets of 4.
Thank you for the reply and photo,..Things are alot clearer now that I've had a few days to digest the info and reread your posts many times....I'm sure that I can wire my pack into groups of 4 as per your recommendation..I'll have my andersons' in the next couple of days and I can play and do some trial fit-ups to see how things look in the real world...I will need to make a new top cover for the battery pack...
When I was reading up about bms's I came across many examples of over charging of individual cells...that didn't help me,I was having the opposite problem - the discharging of cells to death...I came away with the impression that maybe 50% of users had problems with the bms that led to damaged cells...many gave up headways and went to lipo to avoid the bms issues.
I inclued 2 photo's of my pack..one showing the bottom with the fibreglass strip with 16 holes@ 20mm dia....The other photo showing cells in place,no busbars in place....I believe this is what you mean when you say 1up,1down,ect,ect?...
Thanks for photo, can see exactly how you have it now. Your battery block looks nicely made. The last time I used expanding foam I spent ages picking stciky muck off my hands - found out the hard way that its best to use disposable gloves first Lol!
So to recap BalacingBus is ok for SLA but Parallel charging is better (as Mik pointed out), especially for Lifepo4.
Group your cells in 4 lots of 12v, each set coming out to a pair of Andersons.(Great thing the way they clip together so you can have a strip of 8, or a block of 4x2 etc.)
Then the corresponding block to the motor connects them in Series.
The block on the charger connects all 4 pairs in parallel to a 12v car charger.
Great thing that a cheap car charger can deliver 10amps, that means each of the sets gets >2amps, so overall 4hr charge even from nearly empty.
Now this only leaves the issue of keeping the cells in each set of 4 balanced. Ive not had issues yet but Ive heard there is a way of passively balancing an individual set of 4 just with resistors/diodes. I think this is an area for exploration. In the meantime it doesnt take much to check them ocassionally.
A single cell charger can be useful for topping an odd cell up, if u PM me ur adress I'll send you one if u wish as I have 15 spare ones from the days I did individual cell charging! (Thats the extremes that my first annoying BMS sent me to LOL!)
Man you must be psychic...Battery chargers was the next thing that I wanted to ask you about...I have a quality 12v 6a charger that I used for charging 12v 80ah agm batteries,I'll start with this to get the ball rolling.
I'll definitely take you up on the single cell charger offer...I'll PM you in the next day or two with my details..Thank you very much for this offer.
My next question is wire guage...my cells are 12a...the andersons are 15a...controller 15-20amp[ it handles the 48v-12a battery pack no problems ]...I am thinking 15a wire from the local auto parts shop...
Any advice would be much appreciated...
Dont confuse the AmpHour rating with AMPS.
I.E. your cells are 12amphours but I would imagine you will be pulling 20amps out of them at peak.
Whats your motor wattage?
ull probably be ok with 15amp Andersons (if your motor is <600W ?), but I went for the 45amp rated ones, they all look the same (maybe the inner connections are thicker?). I'll throw some 45amp Andersons in with the charger when I send it, so you can compare them. Would be interested to know where they diiffer because someone told me all the 15,30,&45 Andersons can interconnect with each other.
I found those Andersons quite fiddly to crimp so good job you have some spares for practice!, but use the thickest wire you can fit in the connectors really. My wire was a bit thin but its still worked ok but my motors only 300w
Yes your charger sounds fine, might just take 5 or 6 hours though for a full charge as each of the 4 sets will only be getting 1.5amps. But slow is good if u dont mind the extra wait.
Thanks for pointing out amps and amphour...I'm at the bottom of the learning curve and have a long way to go with the technicalities and terminologies of the 'E'world...I'm a fitter and machinist by trade.
The rear hub motor that I'm running is rated at 400watts...My set up is what I consider an entry level arrangment...I wanted to learn and make my mistakes with this kit which only cost $400.,before moving up the scale with power and costs...got to walk before I can run.
Your right about the anderson's, They are fiddley buggers and that was the reason I got extra's...another learning curve,LOL...
Hopefuly you got my PM.
Hi, when the single cell charger arrives you could use a few days to individually charge all your cells to full, then you will know you are starting from a balanced position.
It is imperative the crocodile clips on the single cell charger are put on the terminals the right way round. One error may blow the charger.
Easiest way to ensure this is use your voltmeter and measure the voltage across the cell, and then the charger. The reading will either be positive, or negative depending on which way round you have the probes.
Ensure the charger clips orientation gives the same polarity (+ve or -ve) as the cell voltage does.
Also was going to ask how you connect your +ve and -ve leads to the cells in your battery pack at the moment?
I use these Eyelet things (dunno the proper name), handy because yet again with screws no soldering required.
I will be using the same crimping eyelet as per your photo..their cheap and easily available from local auto parts shop...I'm very conscious and watchfull of polarity...I have a white paint pen with which I mark 3 + around the outside of the positive end of each cell....the same thing 3 - at the negitive end...the markings stick out like dogs balls...
If the single cell charger is unmarked I will colour the positive lead red.....so everything should be very clear and idiot proof...
What voltage will the single cell charger stop at 3.6v or 3.7v or more?....What voltage do you charge to?
After you have charged the cells do you connect the cells in paralell to balance out any slight differances?
the +ve and -ve of the original pack was connected together with the flat metal busbars that came with the headway cells..
The single cell charger goes to about 3.7v then the light changes colour.
The voltage of the cell will decline a bit when taken off the charger but no need to parallel the cells afterwards because you know they are full.
If you want you can parallel a few cells and charge them at once, but obviously the amps are split so it will take longer, but it would save you keep watching for when they are done and having to swap them over. If you did 4 at a time it would take a whole day, but then you could have all 16 done within 4 days.
There's a supplier in Australia who is testing out some 25A single cell chargers which will cost about $200 ... still a bit expensive but I'm assuming you wouldn't need to monitor the batteries whilst charging. Otherwise there are some cheap 10A ones on eBay.