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

[fechter]

i was wondering if the new bms will be expandable?

meaning are there going to be 1 or 4 cell modules that are sold separately so additional cells can be added later?

The BMS is definitely expandable. I don't think there is any practical limit on the number of cells. Each 4 cell section can be linked to the others by 4 wires.

If you need more than 24 cells, you can probably find someone who did not need a 4 cell section and use that. Otherwise you would just need to get two boards and use the sections you need. You can also have extra cell circuits that are not used without affecting the active ones.

 

[commanda]

fechter wrote:
You can also have extra cell circuits that are not used without affecting the active ones.

You need to disable the diode matrix on the unused cell circuits, otherwise you'll never generate the all shunts low signal.

Amanda

 

[fechter]

fechter wrote:
You can also have extra cell circuits that are not used without affecting the active ones.

You need to disable the diode matrix on the unused cell circuits, otherwise you'll never generate the all shunts low signal.

Amanda

True. You would need to isolate the the diode matrix on the unused channels. This could be done by breaking the 12v supply bus after the last installed cell.

 

[ejonesss]

correct me if i am wrong buy isnt the shunt low signals set up in an or logic not and logic?

so if just 1 goes low then it stops the load?

as of breaking the 12v bus it can be done with a jumper block


http://www.mouser.com/Search/ProductDetail.aspx?qs=xxdqPuaJ%252ba3D2ZOJktk8rg%3d%3d

http://www.mouser.com/catalog/635/1384.pdf

these are the same type of jumpers used in computers and on the back of a hard drive to set the master,slave or cable select.

fechter wrote:
You can also have extra cell circuits that are not used without affecting the active ones.

You need to disable the diode matrix on the unused cell circuits, otherwise you'll never generate the all shunts low signal.

Amanda

True. You would need to isolate the the diode matrix on the unused channels. This could be done by breaking the 12v supply bus after the last installed cell.

 

[Patriot]

GGoodrum,

Not to inject unwanted info, veer off course from the original topic, nor press you for time.....

However, after turning on the tv today and seeing the stock market collapse, along with OPEC planning a meeting to cut production to keep oil prices high......

Your little BMS may be a needed item fairly soon. More so than most of us may think.


Anyway, I'm interested in your current testing of the final design.

Also, any idea as to what you may want to charge for them?

Will you be selling them as a kit, or as a fully assembled item?

P.S. Nice schematic. I'll have to sit and do some learning to analyze your work. Very nice inded.

 

[methods]

I wouldn't recommend those at all.

In a high vibration environment those jumpers will work themselves right out. I once had a 5V BEC circuit in a pylon plane that had a jumper like that. Worked loose and I ended up picking up the pieces with a broom.

If you want to change it back and forth I would use a SPST switch with a very stiff spring/slide.
If you want to set it up once or twice just use a bus wire that you can nip then re-solder if needed.

-methods

 

[GGoodrum]

fechter wrote:
You can also have extra cell circuits that are not used without affecting the active ones.

You need to disable the diode matrix on the unused cell circuits, otherwise you'll never generate the all shunts low signal.

Amanda

True. You would need to isolate the the diode matrix on the unused channels. This could be done by breaking the 12v supply bus after the last installed cell.

The idea is to cutoff the unwanted 4-channel sections. Also, the only way you need to worry about the unused channels, is if the matrix parts for those channels are populated. Why would you partially populate unused channels? :?

The ANY SHUNT ACTIVE logically "OR"s the signals from each channel. The ALL SHUNTS ACTIVE signals are logically "AND"ed. Both signals are active low.

-- Gary

 

[PJD]

Richard wrote:

Actually, changing the resistors would be a real pain. Paint is not a bad idea...

Maybe it's a civil engineer's thing, but changing the resistor value is simply more elegant than jury-rigging with paint and wouldn't be too hard if you bend the LED's over a bit.

Also, would this have any beneficial effect of the small temperature-dependence of the shunt voltages, a possible cause you described back here:

http://endless-sphere.com/forums/viewtopic.php?f=14&t=5416&st=0&sk=t&sd=a&start=285 ?

But don't get me wrong; if I am bring up such a small issue it is because the BMS's are otherwise working so well!

 

[ejonesss]

i think small capacitors could be connected to the leds to prevent them from flickering and they would pulse more like the sleep indicator on the macs like the older imacs if they do at all.

as of the other post from patriot
i agree.

not just for the sake of opec and the economy but there are some who dont want to or cant get a drivers license and an electric bike is their only choice since it can be used without having a drivers license or registeration.

i to am looking forward to getting the board and hope it comes out soon.


as of a kit GGoodrum said that would add cost and time and it is easier and faster to include a parts list.

GGoodrum,

Not to inject unwanted info, veer off course from the original topic, nor press you for time.....

However, after turning on the tv today and seeing the stock market collapse, along with OPEC planning a meeting to cut production to keep oil prices high......

Your little BMS may be a needed item fairly soon. More so than most of us may think.


Anyway, I'm interested in your current testing of the final design.

Also, any idea as to what you may want to charge for them?

Will you be selling them as a kit, or as a fully assembled item?

P.S. Nice schematic. I'll have to sit and do some learning to analyze your work. Very nice inded.

If I may bring the topic back to the existing BMS, can anyone explain the effect I described in my post on Sep 01, 2008 1:02 pm (item #2).

Is this just an expected effect of the heating of the reference voltage resistors or other parts on the board?

Also, the shunt leds on my board operate with a very pronounced strobe-like flicker - maybe 30hz or so. Any concern about this condition?

Thanks.

The change in voltage set point with temperature is most likely due to the temperature coefficient of the orange LED, which is acting sort of like a zener diode in this application. While this is undesirable, the amount of drift is probably not enough to be a problem. Locating the heat producing parts away from the heat sensitive parts is always a good idea.

A fan wouldn't be a bad idea.

In future versions, I suppose there could be a way to compensate the voltage better.

The 30hz strobing is OK. With smaller cells, this is fast enough that you can't see it. It becomes a problem if the switching frequency gets too high. Under some conditions, I've seen it flash even slower, like 10hz, which won't hurt anything.

I'm looking at additional circuitry that will terminate the charge once all the shunts are full on. I don't think it will matter to the cells much, but will reduce heat generation once the pack is fully charged.

 

[GGoodrum]

Anyway, I'm interested in your current testing of the final design.

Also, any idea as to what you may want to charge for them?

Will you be selling them as a kit, or as a fully assembled item?

P.S. Nice schematic. I'll have to sit and do some learning to analyze your work. Very nice inded.

I should be getting the "final" version of the boards today. I just got four made, just in case something else has to change. Richard and I will build up complete boards, to try on real packs, this weekend. As soon as we verify that everything works, just like his "blender" version, and that I haven't screwed something up in the layout, we'll be done. I will then order a large quantity of the boards, on Monday. It will take about a week to get the boards back.

As I've said a few times now, what I will offer is the boards, a set of instructions and a Mouser parts list in a form that can be auto-entered as a bill of materials (BOM...). The price is not set yet, as I don't know what it is going to cost me to get the boards done just yet. This is going to be a factor of quantity ordered. In the small quantity that I just ordered, it costs about $75 each. I'm hopeful that I can keep the price down under $50. The parts, for a 16-channel version, costs about $60, I think.

-- Gary

 

[Patriot]

Ha, GGoodrum,

I ran across a website a week ago with a BMS for sale.

Little did I realize, it was your site. I feel like a bafoon now.

btw, do you by chance recommend an inexpensive charger to go with your new BMS?

I was thinking of using the one Ping has for his batteries, as they can be picked up off Ebay for about $20. But, wondered if you had something better to recommend. I wanted to carry the charger with me, so small and light is preferable.

I've been sitting around wondering which battery to get for my bike, but now I am getting excited that I can actually get the battery I've been wanting, since a decent BMS is going to be available to us now.

You're doing everyone in the ebike community a real service with your work. I sincerely hope that if your product proves to be what th eindustry needs, it'll allow you to capitalize effectively with appropriate reward, yet still providing affordable gear for everyone who wants it. The future is bright.

 

[PJD]

i think small capacitors could be connected to the leds to prevent them from flickering and they would pulse more like the sleep indicator on the macs like the older imacs if they do at all.

This would be difficult. Also, I was curious about Richards explanation of the shunt voltage temperature dependence.

 

[rf]

I need a power supply to go along with this BMS in a 20-cell (A123) configuration. Looking at switching power supplies, ~72-volt models are hard to find. Three 24-volt units in series seems like a reasonable solution. Trimmable for an extra volt or so. 48-volt units are available too. Any reasonable way to use a 24-volt and 48-volt model in series to reduce cost and size?

What kinds of problems do I need to be aware of? Any vendor/model suggestions? Cheap, small and light are primary criteria.

Thanks

Richard

 

[dnmun]

richard, why not ask mr ping or ecrazyman if they can build a 72V 24cell lifepo4 charger? they both make 48V chargers and shenzen has a 48V power supply too, so maybe they could find a transformer and parts to get to 88-90 volts using the same box and pcb. maybe if enuff people would commit, he may build up 20-30 chargers for the 24 cell BMS.

 

[jeffkay]

Elite Power Solutions (I am a customer, not affiliated) has good prices on LiFpo4 chargers with nice specs. Don't know if they will work well with the Goodrum BMS but for example the TLS48-15 is a 110v/15A charger outputting 58.2 volts and is about $165 US. Seems like a good deal. They have many others. These are made for the Thundersky Lifepo4's... http://elitepowersolutions.com/products/index.php?cPath=9&osCsid=c117873d20da25897786e7a0da425318
Jeff K.

 

[fechter]

i think small capacitors could be connected to the leds to prevent them from flickering and they would pulse more like the sleep indicator on the macs like the older imacs if they do at all.

This would be difficult. Also, I was curious about Richards explanation of the shunt voltage temperature dependence.

According to the datasheet, the forward voltage for the orange LED changes with temperature. In thinking about it, this should not affect the cell voltage, since that is controlled by the LM431 (those could be a bit temp dependent also). It would affect the charging current when the shunt was active, lowering it a bit when things get hot, which I guess is not all bad.

As far as charging supplies goes, anything that delivers about 3.67v times the number of cells should be good. If the charging supply voltage is too high, it should not matter much as the BMS will throttle it. It would only be a problem if the voltage was too low.

The one from Elite Power Solutions looks pretty good.

You could use switching power supplies in series to get the desired voltage as well. The only problem with some of these is they go into a 'hiccup' mode if the current is too high. Some of them have a shunt and will do a constant current very nicely. You could also modify it to do CC.
If a SMPS goes into hiccup mode, it won't hurt anything (in theory) but it will make the charging process take longer.

 

[rf]

richard, why not ask mr ping or ecrazyman if they can build a 72V 24cell lifepo4 charger? they both make 48V chargers and shenzen has a 48V power supply too, so maybe they could find a transformer and parts to get to 88-90 volts using the same box and pcb. maybe if enuff people would commit, he may build up 20-30 chargers for the 24 cell BMS.

Thanks for the post. I forgot to mention I'm looking for a charger/power supply that will charge my 20s4p A123 pack in around an hour or less (between 6 and 10 amps I think.) From what I've heard the ping chargers take all night (1 amp?) I already have that capability with some Voltphreaks single cell chargers.

There appear to be lots of switching power supplies around to choose from. With Gary's BMS they can probably become first-rate chargers. I'm just trying to learn more about the limitations of that scheme. If I build up a ~74-volt supply that includes a 24-volt one within it then I might be able to charge my electric skateboard with it too. Or perhaps various other odd vehicles that I build in the future. The flexibility is attractive.

Richard

 

[GGoodrum]

Elite Power Solutions (I am a customer, not affiliated) has good prices on LiFpo4 chargers with nice specs. Don't know if they will work well with the Goodrum BMS but for example the TLS48-15 is a 110v/15A charger outputting 58.2 volts and is about $165 US. Seems like a good deal. They have many others. These are made for the Thundersky Lifepo4's... http://elitepowersolutions.com/products/index.php?cPath=9&osCsid=c117873d20da25897786e7a0da425318
Jeff K.

That actually does look pretty good, much like a Zivan NG1, but about 1/3rd the cost. The voltage is a bit low, at 58.2V which is 3.63V per cell, but I'm guessing there is a trim pot that might let the voltage be adjusted up a volt. With the selected divider resistor values of 180k/75k, in the BMS shunt logic, the crossover voltage is about 3.69V, so what turns out to be optimum is slightly over that, or about 3.70V per cell, or 59.2V. You could lower the crossover voltage by using something like a 65k value in place of the 75k.

For a good portable charger, one I like a lot is the Soneil 4808SRF. It can be tweaked up to 60V and the max current up to about 4.5A.

-- Gary

 

[rf]

Elite Power Solutions (I am a customer, not affiliated) has good prices on LiFpo4 chargers with nice specs. Don't know if they will work well with the Goodrum BMS but for example the TLS48-15 is a 110v/15A charger outputting 58.2 volts and is about $165 US. Seems like a good deal. They have many others. These are made for the Thundersky Lifepo4's... http://elitepowersolutions.com/products/index.php?cPath=9&osCsid=c117873d20da25897786e7a0da425318
Jeff K.

That actually does look pretty good, much like a Zivan NG1, but about 1/3rd the cost. The voltage is a bit low, at 58.2V which is 3.63V per cell, but I'm guessing there is a trim pot that might let the voltage be adjusted up a volt. With the selected divider resistor values of 180k/75k, in the BMS shunt logic, the crossover voltage is about 3.69V, so what turns out to be optimum is slightly over that, or about 3.70V per cell, or 59.2V. You could lower the crossover voltage by using something like a 65k value in place of the 75k.

For a good portable charger, one I like a lot is the Soneil 4808SRF. It can be tweaked up to 60V and the max current up to about 4.5A.

-- Gary

The Elite TSL60-15 ($239) looks like it might be okay for my 20s4p pack. Assuming 15-amps isn't too much for the BMS or the A123 cells. That appears to be the lowest power 72+volt charger they have. (A half-hour charge time would be pretty cool.)

http://tinyurl.com/3upqrm

I've also seen some 24-volt switching supplies for less than $30 each. Three of those would be less than half the cost of the Elite. Hmm. What to do ...

Richard

 

[GGoodrum]

The Elite TSL60-15 ($239) looks like it might be okay for my 20s4p pack. Assuming 15-amps isn't too much for the BMS or the A123 cells. That appears to be the lowest power 72+volt charger they have. (A half-hour charge time would be pretty cool.)

http://tinyurl.com/3upqrm

I've also seen some 24-volt switching supplies for less than $30 each. Three of those would be less than half the cost of the Elite. Hmm. What to do ...

Richard

15A is fine, but you will need to use the "extra" charge power leads, with 12-14-gauge wire. The Molex-type connectors are good for up to about 9A.

The same comment applies about tweaking the voltage up a volt, or so, or you would need to change the lower value divider resistors.

 

[rf]

15A is fine, but you will need to use the "extra" charge power leads, with 12-14-gauge wire. The Molex-type connectors are good for up to about 9A.

The same comment applies about tweaking the voltage up a volt, or so, or you would need to change the lower value divider resistors.

Okay.

No need for extra heat sinking?

I'll ask them about tweaking the voltage up a bit.

Thanks, Gary.

Richard

 

[GGoodrum]

No need for any heatsinking. By the time the shunts start kicking in, the current won't be anywhere near what it starts out at. The shunts will bypass a maximum of about 1/2A which is easily dissapated without a heatsink.

 

[ejonesss]

broken link

The Elite TSL60-15 ($239) looks like it might be okay for my 20s4p pack. Assuming 15-amps isn't too much for the BMS or the A123 cells. That appears to be the lowest power 72+volt charger they have. (A half-hour charge time would be pretty cool.)

http://tinyurl.com/3upqrm

I've also seen some 24-volt switching supplies for less than $30 each. Three of those would be less than half the cost of the Elite. Hmm. What to do ...

Richard

15A is fine, but you will need to use the "extra" charge power leads, with 12-14-gauge wire. The Molex-type connectors are good for up to about 9A.

The same comment applies about tweaking the voltage up a volt, or so, or you would need to change the lower value divider resistors.

 

[dnmun]

the shenzen 48V10A power supply is a switcher i think. so i figured those guys could be the best place to go since keywin seems to understand the value of working with this group.

a 72V battery is a 24 cell pack, and it actually needs 90V DC to charge the entire pack of lifepo4, and 101V to charge the 4.2V lipo or limn. i was thinking that this would be something that shenzen could do and be able to push at least 10A with the current set of boards they have. i think it may require a critical mass of people ordering a hand built charger in order to have them consider it as a new product. but i am now convinced that 72V will become the new standard for high performance because of the availability of this board. i had expected 48V to be the most comfortable place to stay because of all the equipment now built to 48V. now with this board, i can see that there will be demand for 72V chargers capable of high current. that is why i thought ecrazyman would consider building some using their current pcb and boxes for their power supplies.

i would even like for ecrazyman to consider building a combined controller/charger in one box so that the charger could always be carried on the bike with minimal additional weight added. since the cables from the battery already run to the controller, and maybe some of the capacitance in the input of the controller could help smooth the charge current. or justify larger caps that could be shared on the battery cable itself. maybe it could be done with only 4-5lbs added including a short AC cord, make it 120/240V selectable for international use.

 

[michaelplogue]

RE: 72V charger....

http://elitepowersolutions.com/products/product_info.php?cPath=9&products_id=60&osCsid=c117873d20da25897786e7a0da425318

A bit expensive and out of stock, but at least there is something out there on the market....


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