Even Newer 4 to 24-cell Battery Management System (BMS)

[commanda]

commanda,
The specs quote a "Hiccup" overcurrent protection mode. How does this affect charging?
I was also looking at this site for Meanwell supplies for my charger. I need 29.7 volts (8s5p) and was looking at the larger model (27VDC, 150W MPP238 - $65.94 +GST) as it could be adjusted up to ~30V and had Current Foldback rather than Hiccup mode. But it is twice the price. Have you adjusted the voltage output? I'd really like to know if it can get to >29.7V and how Hiccup affects the BMS and the charging process as this model is much cheaper.
JohnB

I'm actually building my BMS slightly differently to the design in this thread. I'm putting constant current sources in the common control part of the BMS, so the switchmode supplies never run on their current limit. This makes my choice of supplies as "almost anything".

The 2 current sources are approx 4A and 2A, in parallel. Initially, they're both on, charging at 6 amps. Any shunt low turns off the 4A. All shunts low then turns them both off, after a time delay of approx 15 minutes. RS flip-flop so that when it completes charging, it stays off until the power is cycled. Only half built yet. Gotta get a move on though as my batteries should be on my doorstep tomorrow or Monday.

I'll fire one up and get the max voltage figure for you.

Amanda

 

[commanda]

commanda,
I'd really like to know if it can get to >29.7V
JohnB

I'll fire one up and get the max voltage figure for you.

Amanda

28.88 volts no load.

Amanda

 

[fechter]

I did more testing today and think I have it pretty much dialed in now.

Twisting the leads around on the KSA931's is sort of a pain, but that's what I did. We can definitely straighten that out on the next version.

The heat is manageable as long as the board isn't sealed up inside a box or something.
If waterproofness is required and it must go in a box, then the lower current shunts are recommended.

 

[JB_EB]

Hi Richard,
Can you please explain how the circuit would work if the power supply voltage was a little BELOW the required string voltage of ~ 3.7V x number of cells?
Eg if an 8s pack needed slightly more than 29.6V from the supply but the supply could only output say 29V, would all cells essentially charge up to the same voltage or would some of the longer charging cells miss out? I'm hoping to reuse an existing LiCo charger that outputs about 29 volts as a booster charger for use at work. I still intend to buy/build a new 30V supply to use for overnight charging at home, so hopefully any small missmatch would be removed each night.
Thanks, JohnB

 

[fechter]

OK, if the charger voltage is a bit low, then some cells would reach the 3.7v set point before others, which would limit the amount of voltage the lowest cells would get to something less than 3.7v. If all the cells were perfectly balanced, they would all take on the same amount of charge and have the same voltage. Of course this doen't happen. Lets say you were .1v short. All the cells except one would reach set point, but the lowest cell would be .1v short of set point. The lowest cell would be missing out. In practice, this might make a very small difference in total capacity, since the cells is mostly charged by the time it gets close to the set point.

You could also use a separate, but weaker supply to finish the balancing and use the larger one for more current during bulk charge. Once the first cell reaches full, the charge current is going to drop down to less than .5 amps anyway.

Most chargers can have their voltage tweaked a bit too.

 

[JB_EB]

Thanks for the explanation Richard. I figured as much. I know that the supplies can be tweaked a bit, but the cheaper "24V" supplies tend to run out of adjustment at around 28-29 volts and the less common 27V supplies that can be adjusted to 30V tend to be much more expensive. Also, many of these switch mode supplies have an overvoltage protection circuit that is set to trip out at around 30V for the 24V supplies and this doubles the difficulty of modifying the 24V supply to get 30V.
JohnB

 

[twit_biddler]

Nice work Gary & Richard!

I hope it's not too much to ask but Is it at all possible to get a good resolution copy of the final artwork (1:1 300dpi+ or Gerber files) and/or schematic?

I've been making two-sided circuit boards at home for years - no nice plated holes like yours unfortunately so construction will be a bit more difficult but not something I can't handle. Also, like others I already have a majority of the components.

TIA -- twit

 

[GGoodrum]

Thanks for the explanation Richard. I figured as much. I know that the supplies can be tweaked a bit, but the cheaper "24V" supplies tend to run out of adjustment at around 28-29 volts and the less common 27V supplies that can be adjusted to 30V tend to be much more expensive. Also, many of these switch mode supplies have an overvoltage protection circuit that is set to trip out at around 30V for the 24V supplies and this doubles the difficulty of modifying the 24V supply to get 30V.
JohnB

What you might do instead is use a bit lower value resistor for the 75k one in the voltage divider. With the 1% 180k/75k we're using now, the cutoff seems right around 3.69V. You could go down to 69.8k, which should drop the cutoff point to about 3.61-3.62V. That would get you closer to 29V. If it is a temporary thing, you coul also use the 75.0k supplied resistors, and then tack on something like a 1 meg in parallel with the 75k. That should get it down to the same range.

-- Gary

 

[sharkmobil]

Sorry if it has been answered/addressed already, but any chance we could have adjustable pots on this board, so it can work with both LiFePo4 and Li-Ion chemistries?

 

[jeffkay]

Gary, Is the kit almost out of the oven? I need to order for "Deep Cycle"...

Jeff K.

 

[GGoodrum]

Gary, Is the kit almost out of the oven? I need to order for "Deep Cycle"...

Jeff K.

Yes, the oven timer just went off...

I'm adding the kits to my website, as we speak, and I'm finishing up the assembly/test instructions. Richard came up with a clever way to test the board with nothing more than the charger/power supply that will be used.

Anyway, give me an hour, or so, and I will post something here.

-- Gary

 

[jeffkay]

Gary and Richard,
Fantastic news. I will be one of the first to apply funds that stop that nasty negative cash flow for this project!
Jeff K.

 

[GGoodrum]

Okay, it's soup... Here's a link: http://www.tppacks.com/proddetail.asp?prod=EBKE%2DBMS%2DKit

Please allow a few days to get the kits together, and shipped. None will go out before Monday, as I ran low on a couple parts, and won't get a new shipment in until Monday.

-- Gary

 

[jeffkay]

Paid ya. Thanks!

Jeff K.

 

[twit_biddler]

Just ordered mine too.

Thanks again Gary, Richard and lets not forget Bob Mcree!.

 

[Jeremy Harris]

Many thanks Gary, Richard, Bob etc. I've just ordered a kit too.

Jeremy

 

[Tiberius]

Hi Gary,

What is shipping cost to the UK? Is it worth combining orders from a few of us here?

Nick

 

[shinyballs]

For my setup of 5p 22s, I would need 2 of these and use a switch to separate the packs into 5p 11s(35.2v) for balancing/charging. As for charger, will use my existing 36v variable power supply, set to 39v. correct?

 

[Jeremy Harris]

Nick,

According to Gary's shop checkout, shipping was a bit over $30. Seems pretty good to me. Total cost came to a bit over £62 according to PayPal's currency conversion.

Jeremy

 

[fechter]

For my setup of 5p 22s, I would need 2 of these and use a switch to separate the packs into 5p 11s(35.2v) for balancing/charging. As for charger, will use my existing 36v variable power supply, set to 39v. correct?

That would be one way to do it. You'll need closer to 41v on charging.
It may be possible to charge both halves in parallel at the same time.

 

[manfred59]

Super!! Many thanks to all who worked hard at this project! :lol:
I am very pleased to be able to order this kit.
I've just ordered two kits !
Manfred

 

[manfred59]

Are there 15 Amp Red/Black Anderson Powerpole plugs on the BMS picture of tppacks.com page?
Would come these Connectors with the set? If not I will order some at powerwerx.com, because here in Austria I won't get some.
Or is there an adress in the UK to order online?
Manfred

 

[gogo]

If I wanted to utilize this device, what are my options for the cells it is compatible with? TIA

 

[GGoodrum]

Are there 15 Amp Red/Black Anderson Powerpole plugs on the BMS picture of tppacks.com page?
Would come these Connectors with the set? If not I will order some at powerwerx.com, because here in Austria I won't get some.
Or is there an adress in the UK to order online?
Manfred

Actualy, I think they are the 45A versions. These don't come with the kit, nor do the wires, but you can use just about anything. I just used them because it was a handy way to do the jumper.

Today I will finish up the assembly/test instructions, and start putting together the kits that have been ordered so far. For those interested, here's what the latest schematic looks like:

What Richard was playing with was the values for R9, C3 and C4. Mine actually had a 10k, for R9, and a .1uF for C3, and it works perfect with my Zivan NG1, but with the new values, it widens the tolerance for charger/supply voltages that are higher than the sum of the shunt cutoff voltages. It turns out my NG1, which tops out at 59.08V is just above the sum of the shunt cutoffs by about 120mV, which is perfect. I put in the new parts and tried it with my HP supply set to the max it would go, which was about 61V and it seemed to work exactly the same, which is good.

Okay, back to work...

-- Gary

 

[GGoodrum]

If I wanted to utilize this device, what are my options for the cells it is compatible with? TIA

With the supplied parts, it is designed to work with any LiFePO4 cells It could also be used with other Lithium-based chemistries, which have higher nominal voltages and charge cutoff points, simply by changing the values of the voltage divider resistors (R1 and R2). The 180k/75k values supplied will divide the cell voltage down to the 2.5V level the LM431 regulator requires. The value this ends up being at the cell is about 3.69V. You could adjust these values to match the 4.1V or 4.2V that other Lithium chemitries require.