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

[Doctorbass]

Thanks Fechter,

I'll try that.

so the 4110 may be better? the rds ON is very close to the STP160...? so what would be the difference.. I have alot of 4110 here..

doc

 

[Patriot]

I have a couple questions/issues.

I've noticed with my BMS, that I need to turn up the voltage on my chargers to about 60.5v to get them to fully trip the main LED green to turn off after balancing.

On many ocassions, the individual channels light up fully, and the cells appear to be balanced, but the main LED won't trip. Thus, the BMS resistors keeps bypassing for an hour or so.

Even with the voltage turned up, it can take up to an hour to trip.

I wonder if it is the lower amp rate (2a) of my charger that is the problem?

Or, maybe the circuit is getting too hot in the enclosure I built. It gets warm, but not super hot, as the board is sideways with the big resistors mounted up to let the heat rise out of the enclosure.?

The charger needs to supply over 1/2 amp (or whatever the shunt current is) at the peak charging voltage in order for the auto shutoff to trip. The BMS circuit will regulate the voltage, so the charger can be cranked up way over the minimum voltage without damaging anything. If your charge current tapers off too much toward the end point, it might not have enough current to trip the auto shutoff.

You can test by measuring the charging current with an ammeter.

The voltage set points may change slightly with temperature, so this could be part of it.

On a similar note, Nate sent me his board after trying to troubleshoot remotely for quite a while. I found that everything was working properly, but the red/green LED is difficult to read. When it is slightly green (according to the signals going to it), it still appears solid red to the eye. I guess this can be real confusing. In the future we may recommend a water clear version or separate red and green LEDs to make it easier to read.

Also the voltage settings on all the cells are slightly higher then I was expecting based on past builds. His board is averaging 3.7v +/- .02v per cell, which should be just fine for the batteries, but in the past I've gotten closer to 3.68v. Not a big deal, but I may consider changing the divider resistor to bring it down a bit. This could be largely due to tolerance variations in the resistors or the LM431's.

With my board, I noticed that when all leds are lit, the main will sometimes blink, as if it wants to trip, but eventually, it just doesn't. It stops blinking, then goes back to red. After about an hour, the charger itself trips off on full charge. Basically, it trips before the BMS, because it obviously trips when amp rate is almost nothing from the charge being complete. yet, the BMS stays red, and once the charger trips, all the channel leds will go out as expected.

I think it may be as you said. The charge current may be tapering off so slowly, that it isn't tripping the main LED.

Either way, I am going to drill some more air holes in my BMS enclosure for the lower half to get more natural circulation air to keep it cool. Also, even though the main LED isn't tripping, I can at least feel good that the cells are basically balanced, because all channels are fully lit prior to the charger tripping off.

 

[CamLight]

My two 14s(partial 24s) BMS are tested and 100% functional :wink:

now it's time to connect to the battery... but i just wonder... What is the continuous charging current max that the STP160N75 FET can take ?

according to the SOA curve, if i charge at 51.8V CC-CV, the max current posisble is 9A at 10ms pulse

But i want 20-30A charge...

any suggestion.. data?

Doc

Hi Doc,
That SOA graph is for plotting the power a FET can handle while in its linear region, not when it's being switched on/off. For a 10mS wide pulse, the time the FET spends being linear is probably microseconds (with a good MOSFET driver) or just a few milliseconds (driven with a MOS/TTL gate or a PIC).

As fechter mentioned, the principle source of heating will be the on-state resistance (Rds-on) of the FET. When doing any calculations, remember that the resistance can double (or more) over its 25 degree-C spec. Also be sure to use the "max" Rds-on value, not the "typical"value before doubling it.

 

[CamLight]

Thanks Fechter,

I'll try that.

so the 4110 may be better? the rds ON is very close to the STP160...? so what would be the difference.. I have alot of 4110 here..

doc

Check the data sheets. See which has a lower max 25C Rds-on value and which is less sensitive to changes to the on-resistance as it heats up (Rds-on vs. Junction Temp graph). Then carefully check the thermal resistances of the two FETs. You can have a FET with a Rds-on double that of another but it will still run cooler if it's more efficient at moving that away to a heat sink.

 

[rsisson]

Can you put several of these in Series to charge even larger Voltage packs? I am looking at a 40-Cell (120V) pack for an EV car...

You also mentioned some mods for larger current packs, but I never saw a follow up on that item?

(My target pack is a 120V (40 Cell) 150Ahr Blue Sky Pack)

 

[fechter]

Can you put several of these in Series to charge even larger Voltage packs? I am looking at a 40-Cell (120V) pack for an EV car...

You also mentioned some mods for larger current packs, but I never saw a follow up on that item?

(My target pack is a 120V (40 Cell) 150Ahr Blue Sky Pack)

You should be able to add cell circuits up to 40s. The only real mod would be to use a higher voltage FET for the charge control. Since the FET only sees the difference between the pack voltage and the charging source, an IRFB4110 should work, but you'd have to be careful when testing without cells connected as you could exceed the voltage rating of the FET. With no cells attached, the FET sees the full charger voltage. You could also use a 150v rated FET, but the maximum charging current would be lower due to increased heating. Depending on your max charge current, you may also need to add a heat sink to the FET. With a 4110, I think you can run 20A without a heat sink.

An alternate approach is to split the pack into two halves and use two chargers and two boards in series. As long as the chargers have isolated outputs, this would work fine. Using this approach, there is no limit to the number of cells.

 

[fechter]

Update on troubleshooting Nate's board from back on page 78-80,

It seems Nate accidentally installed the LEDs backward initially, then corrected the mistake. Apparently the reverse polarity did something weird to the LEDs, causing their forward voltage to increase significantly. Normally they should be around 2.0v when lit, but some of Nate's were as high as 2.5v, which causes the auto shutoff to not work properly. This is really strange, since the LEDs look like they light up normally, but they just have a higher forward voltage. I replaced a few of the highest ones, but I think I will need to replace all of them to get the voltages matched close enough.

Gary is going to update the instructions to indicate that the shorter leg on the LED goes to the square pad and the longer leg goes to the round pad. This should clear up some confusion, as the new LEDs don't have a flat side.

 

[GGoodrum]

Instructions updated. Here's a link: 4-24 - Cell LiFePO4 BMS-v2.5 Kit Assembly-Test Instructions.

-- Gary

 

[rsisson]

I took a look at the "Assembly Instruction" which also included the latest schematic....

While the Shunt portion of the BMS looks like it would be fine for the final balancing portion of the charge, I don't think the FET, even with a HeatSink will be even close to handling the Full (bulk) charging current on a CAR sized pack (150-180Ahrs) as that would be 75-90 AMPS at .5C which is typical if you have access to a big 220V charger.

I was planning to have an additional "dryer" circuit put in the garage, and 40A of 220V would give me ~80A at 120V... OUCH. the same charger limited at 110V household circuit would be limited to 12-15A, well within your circuit...

But what to do on the BIG charger...

SOME of the Big chargers have inputs for going to the next phase and shutting down...

Obviously, if the charger could be "throttled" from Bulk >> Top-off when "any shunt" went active and shut down or final stage at "All Shunt" I could MOST of your circuits....

The main SHUNT looks a lot like the Metric Mind Clamp Module that he designed to go on each cell... and then he had the Opto outs as well...

Its a matter of taking the 100-series parts and putting them on a cell topper board (or board with a tail) and then daisy chaining the optos to a "master" that talks to the charger... but I doubt that any FET could take the Full output of a big Zivan, Manzanita or Rusco charger

What are other BIG PACK (150-180Ahrs) people doing?

 

[fechter]

You might black out the entire neighborhood with that

If you modified the circuit to use 4 FETs in parallel, it should handle 80 amps no sweat. I think you'd need to mount them offboard and bring the gate drive and ground over.

If you can interface the optocoupler outputs to the charger circuit to throttle the output, that would work, but nobody has tried that before and it will depend on the charger.

Another option is to use the big charger for bulk charging up until the first cell reaches target, then switch over to a smaller charger for balancing.

 

[northstar]

getting 19 X 60 AH TS pack and was considering shunt type system instead of true BMS. Do you have a BMS for such a pack and how much would it cost? also wondering about a charger for such 19 X 4.25v=80.75v, I don't know if they top up this way or not? Will use for lightweight daily driver most of the time in warm season, and temps below 0 deg. Cel will occur winterlong. Min. temp maybe -15 deg Cel. Hope to have system on line by mid- july or so... Thank for the help, hope to get a BMS soon...

 

[rsisson]

Over of the EVDL list, which is more for Car and Truck type EV's, the chargers of choice are Zivan, Manzanita or Rusco. Depending on your source voltage they are capable of 60 or even 80 amps, so the 30A (.5C) needed for a 60Ahr pack would be easy.

I am looking into a "hybrid" system using the "Clamp/bypass" from here and the intelligence of the chargers. Combine that with the LVC as an input to the controller somewhere and the pack should be well protected... I am going to let the controller limit current as I can set both continuous and "boost" limits.

A different FET, of maybe just putting the spec'd one on a heat sink and you should be in the 20-30 amp range... the 80V should not be a problem so long as you keep everything cool....

Oh...over on the EVDL list, 150Ahrs is SMALL... there are people with Big pickup trucks with 1,000-1,500 of Flooded lead cells in/under the bed, 1,000 Lbs of Nicads, Or MnNh or even some 260Ahr LifePo4 packs... All of those are capable of some really serious currents, mostly 2/0 wires connecting things...

Same problems with Batteries though... the weakest one sets the pace, and balancing is KEY... LVC, charging profiles,temperatures, etc...all the same...just move the decimal over on the currents (and the $$)

 

[fechter]

The design of my circuit is certainly scalable. If there was enough demand, I could do a cell-top version with the appropriate control circuit. It is much better to interface to the charger than to try and regulate it outboard, so it may be necessary to modify the charger to install an interface. This should not be too hard, but it will be different with every charger. Outboard can work too, it will just be larger and more expensive.

 

[GGoodrum]

Most of the higher power chargers usually have two, or even three charge profiles. My Zivan has a a main constant current mode at the full current, but once the cells get to about 70-80%, it throttles back to about 1/3rd the current, where it stays until it hits the CV limit. One workaround would be to bypass the BMS during the first CC phase, until it gets to the throttle point, and then let the BMS control the rest of the charge.

-- Gary

 

[proempiet]

I can not get my BMS to work.
Fetcher help me a lot but I have no good testing equipment and my scooter an Extreme Xm5000-Li with 60Ah Thundersky batteries and Thundersky Charger seem to do a good job in stying the pack ballanced.

If anyone wont to buy my 24 Cell (21 installed but all components (minus some resistors) are there) my BMS please sent me an PM or an email on
Beunesto at gmail dot com

http://picasaweb.google.com/Beunesto

 

[methods]

You should put that post in the for-sale section.
Add a few close up pictures and I am positive you will be able to make a sale.
Good luck and sorry it did not work out for you.

-methods

 

[rsisson]

What I really want is a "Battery Top Clamp/Shunt" similar to the picture.

OR.. A version that would bolt to ONE terminal and have a pigtail to the other to allow for varying size batteries.

Each would link to it's brethren with a 4 pin cable and then to link to a "master" controller that gives me signals for

1 - Low voltage cutoff
2 - Any Shunt Active

Contact closures would be best, as almost ANY charger can be made to take that, and I know my controller would take that as a "brake" signal....

My controller can take of discharge current control, and it will do it gracefully; not shutting down suddenly in the middle of an intersection (wasn't THAT interesting!!!)

Advantages...100% scalable if all you want is BRAKE and "SHUNT ACTIVE" they can all daisy chain at the LOW VOLTAGE OPTO level...
Adjustable Sizes... you have the space for larger Resistors, FETS or possibly heatsinks...
Low voltage... the MOST voltage any board can see is the voltage of it's battery...4V... No High voltage potential...

Many solutions LOOK good, until you try to connect them to a terminal that already has a 2/0 wire and 3/8" ring terminal on it...

Just my $.02

 

[Patriot]

I have a couple questions/issues.

I've noticed with my BMS, that I need to turn up the voltage on my chargers to about 60.5v to get them to fully trip the main LED green to turn off after balancing.

On many ocassions, the individual channels light up fully, and the cells appear to be balanced, but the main LED won't trip. Thus, the BMS resistors keeps bypassing for an hour or so.

Even with the voltage turned up, it can take up to an hour to trip.

I wonder if it is the lower amp rate (2a) of my charger that is the problem?

Or, maybe the circuit is getting too hot in the enclosure I built. It gets warm, but not super hot, as the board is sideways with the big resistors mounted up to let the heat rise out of the enclosure.?

The charger needs to supply over 1/2 amp (or whatever the shunt current is) at the peak charging voltage in order for the auto shutoff to trip. The BMS circuit will regulate the voltage, so the charger can be cranked up way over the minimum voltage without damaging anything. If your charge current tapers off too much toward the end point, it might not have enough current to trip the auto shutoff.

You can test by measuring the charging current with an ammeter.

The voltage set points may change slightly with temperature, so this could be part of it.

On a similar note, Nate sent me his board after trying to troubleshoot remotely for quite a while. I found that everything was working properly, but the red/green LED is difficult to read. When it is slightly green (according to the signals going to it), it still appears solid red to the eye. I guess this can be real confusing. In the future we may recommend a water clear version or separate red and green LEDs to make it easier to read.

Also the voltage settings on all the cells are slightly higher then I was expecting based on past builds. His board is averaging 3.7v +/- .02v per cell, which should be just fine for the batteries, but in the past I've gotten closer to 3.68v. Not a big deal, but I may consider changing the divider resistor to bring it down a bit. This could be largely due to tolerance variations in the resistors or the LM431's.

So, simple questions.

If I charge regularly, and only get a main LED trip to green say, every three or four charges.. is it ok for me to run like this?

The channels cells all fully light up when charging, before the charger trips on its own. It's just the Main LED doesn't trip.

So is that good enough for balancing?

 

[recumbent]

Why does my BMS not want to balance my cells?

Half, (8) orange lights will go on, then the voltage of the orange-lit cells rise rapidly, as if the voltage is being directed only to them. Then the green light comes on and the charger stops.
eventhough i manually ballanced the cells the day before.

The 8 or so cells that have tripped the orange lights have skyrocketed voltage readings on my lifepo4 cells. I don't get it? It does the complete opposite of ballancing.

Did i mount something backwards?

I hope this makes sense.

 

[steveo]

Hey Gary

Just a quick question, Has the BOM on mouser Changed for the 2.5version? .. if so what are the extra parts that i would not need to order specifically .. I just want the first channel spare parts ..as i burn out a channel .. when one of my battey packs disconnected. .. i have version 2.3

-steveo

 

[fechter]

So, simple questions.

If I charge regularly, and only get a main LED trip to green say, every three or four charges.. is it ok for me to run like this?

The channels cells all fully light up when charging, before the charger trips on its own. It's just the Main LED doesn't trip.

So is that good enough for balancing?

That's probably fine as long as all the cell LEDs light up. The charger's built in auto shutoff is just kicking in a bit earlier than the one on the BMS board. You could possibly increase the charger voltage a bit to overcome this, but probably not worth the effort.

 

[fechter]

Why does my BMS not want to balance my cells?
Did i mount something backwards?

I hope this makes sense.

Sounds like it, or some other kind of problem. I always recommend testing the board with no cells attached first to make sure everything is working. A current limited adjustable power supply is even better for testing.

With no cells attached, if you connect the charger, all the LEDs should light up then trip the shutoff.
The auto shutoff should not trip until all the cell LEDs are fully lit.

 

[dnmun]

risson, you should be able to carry enuff 240V power out there if you have a dedicated circuit already. do you really have to hire an electrician or can you do it yourself?

you can take a dedicated circuit from your service panel to the garage and convert it from 120 over to 240V. find the first outlet junction box in the line from the service panel and open it up and make that into a 'subjunction box'. then bring 240 to that box from your service panel by using 2 adjacent circuit breakers on white and black. then in the subjunction box you will have 240V between black and white, and you can then wire the tail end of that circuit back to 120V again by wiring the white and ground of the following section to the ground in your 'subjunction box'. then the black wire of that tail end section can be attached to either the black or white of the 240 in the 'subjunction box'.

i always solder connections myself and have no trouble running 40A in 12G cable without the slightest concern about overheating, but i do solder the junctions.

40A at 250V is 10kW. 13.4hp.

 

[steveo]

Hey Gary

Just a quick question, Has the BOM on mouser Changed for the 2.5version? .. if so what are the extra parts that i would not need to order specifically .. I just want the first channel spare parts ..as i burn out a channel .. when one of my battey packs disconnected. .. i have version 2.3

-steveo

bump?

-steveo

 

[methods]

The V2.5 BOM appears to be here.

-methods