BalacingBus (no BMS), Positive feedback

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!

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!!

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, 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

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!

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?

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?

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.

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.
http://cgi.ebay.co.uk/Intelligent-Automatic-battery-charger-10A-6v-12v-24v-/290548984771?pt=UK_Campervan_Caravan_Accessories&has...

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!)

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.

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.

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.