BMS suitable for super capacitors

[Archerite]

I have a few super capacitors and want to make a module out of it with an actual BMS to balance the voltages between the cells.

I have loose 500F 2.7V supercaps that I have done some experiments with. No protection circuit yet. Charged with a bench powersupply tot 2.6V manually until no more current was drawn.

I also have 4 modules that are rated at 16V that do have protection circuits with a resitor and mosfets I think. Each module has 6 2.7V 10F capacitors. Small...but also affordable because of it.

My main goal here is learning, experimenting but eventually also to actually use them for something...ehm...useful. First idea is as a power buffer for handcrank generator. And hydro/gravity based generators to capture all energy and keep a more constant voltage.

At the same time...the inbalance between individual caps concerns me a bit. So I am looking for a BMS that can both monitor, protect and balance cells between 1-2.7V Most cheap ones are meant for the lifepo4/li-ion battery voltages 2.5-4.2V

Is there already something that exists that can be configured to work with these specific voltages? I am considering (yet another projecta) and design one myself. Hopefully with help and suggestions from this forum.

Thanks in advance.

 

[sunshine_eggo]

A LTO BMS might work. LTO typically run 1.5-3.0V at the extremes.

 

[Warpspeed]

One very simple low cost and effective way to prevent super caps from drifting too far out of balance over time, is to simply connect an appropriate LED across each cap.
Depending on the actual working voltage range, you select an appropriate colour of LED.
The current rises very steeply (and the LED gets brighter) across any cap that has a slightly higher voltage than the others.
Its not a lot of power, but over days, weeks, and months, it easily balances any slight difference in leakage current in the caps.
Hint... buy all the LEDs plus a few spares from the same batch, they will be better matched.

 

[cs1234]

Would a BMS be able to handle the amperages on charge/discharge from a bank of super caps? Can you only use the balance leads of the BMS and not use the charge/discharge portion?

 

[Archerite]

A LTO BMS might work. LTO typically run 1.5-3.0V at the extremes.

I have looked at some LTO BMS's that might be suitable...in the price range 50-80 euro's from what I have seen. Also with a high AMP rating ofcourse of 100A or more is what I am looking at. Not that I really expect a super cap bank to hold that much current for long, hahaha

Thanks for the sugestion.

Would a BMS be able to handle the amperages on charge/discharge from a bank of super caps? Can you only use the balance leads of the BMS and not use the charge/discharge portion?

I am no expert...but I see no reason why a BMS rated for 200A would care if that comes from batteries or super capacitors. As long as the voltages of each cell are within the limits of the BMS I think it should be alright.

 

[toms]

The supercaps just need equaliser boards, something like this for each one. The factory Maxwell series supercaps have something similar (which you can buy from fpvpower.com.au)

 

[sunshine_eggo]

I am no expert...but I see no reason why a BMS rated for 200A would care if that comes from batteries or super capacitors. As long as the voltages of each cell are within the limits of the BMS I think it should be alright.

Pure speculation: Like fuses/breakers and their AIC rating, while a BMS might be able to sense a short circuit, perhaps the FETs would be unable to interrupt the flow of current from such low resistance elements?

 

[cs1234]

I am no expert...but I see no reason why a BMS rated for 200A would care if that comes from batteries or super capacitors. As long as the voltages of each cell are within the limits of the BMS I think it should be alright.

Unless you are getting them for a really good price it doesn't even seem worth it vs lifepo4 if we're going to "cap" them to 200amps. May as well just get more lifepo4.

Let those caps run wild !

 

[Archerite]

Unless you are getting them for a really good price it doesn't even seem worth it vs lifepo4 if we're going to "cap" them to 200amps. May as well just get more lifepo4.

Let those caps run wild !

I got them pretty cheap I think for about 25-30 euros for 5x 2.7V 500F super capacitors on amazon. I have 10 now and thinking of getting more....but ONLY if I can use them safely and correctly. Meaning both balanced voltages across the cells and protection/prevention of more than 2.7V. A BMS is the only valid option but I did not know if they existed in these low voltage range...until I heard about LTO batteries that have a similar limit. I am thinking of a JK BMS with bluetooth...the limits can be configured I think and hopefully low enough to get more power from the capacitors when needed.

It's not a complete replacement for any lifepo4 but more a complement to them. On one way to experiment and learn from the project and see what's possible. And on the other hand to see if it's an option to handle peak loads I have on my 24V system after a DC-DC converter from 12V->24V.

As I said...my main goal is learning and fun. Not an economic low budged option. Would be nice if both were possible at the same time thought ?

 

[toms]

I got them pretty cheap I think for about 25-30 euros for 5x 2.7V 500F super capacitors on amazon. I have 10 now and thinking of getting more....but ONLY if I can use them safely and correctly. Meaning both balanced voltages across the cells and protection/prevention of more than 2.7V. A BMS is the only valid option but I did not know if they existed in these low voltage range...until I heard about LTO batteries that have a similar limit. I am thinking of a JK BMS with bluetooth...the limits can be configured I think and hopefully low enough to get more power from the capacitors when needed.

It's not a complete replacement for any lifepo4 but more a complement to them. On one way to experiment and learn from the project and see what's possible. And on the other hand to see if it's an option to handle peak loads I have on my 24V system after a DC-DC converter from 12V->24V.

As I said...my main goal is learning and fun. Not an economic low budged option. Would be nice if both were possible at the same time thought ?

I’m still not sure why you think that the equalising system used in the factory Maxwell supercaps isn’t suitable.

 

[Archerite]

I’m still not sure why you think that the equalising system used in the factory Maxwell supercaps isn’t suitable.

I never said it wasn't suitable, but besides that I am not from Australia I couldn't find anything on the link you mentioned either:


To me looking at just the picture it looked like a similar thing to the simple cheap "circular boards" I already have that activate a resistor at a voltage above 2.7V with a mosfet/transistor combination. Or something allong those lines.

What I am "concerned" about is that one cell can be 1.5V, another 2.5V and yet another 0.5V. I have a smaller 16V pack of 6 10F super caps with the simple protection circuit. I charged it to 15V and after using it a little bit I measured unbalanced voltages like that. A few were down to 1.1V, others 1.4V and one or two were 0.6V. If the Maxwell circuit board has a balance function to equalize the voltages between the cells...then yes it would be suitable. If it only protects above 2.7V it's not what I am looking for.

 

[sunshine_eggo]

What I am "concerned" about is that one cell can be 1.5V, another 2.5V and yet another 0.5V. I have a smaller 16V pack of 6 10F super caps with the simple protection circuit. I charged it to 15V and after using it a little bit I measured unbalanced voltages like that. A few were down to 1.1V, others 1.4V and one or two were 0.6V. If the Maxwell circuit board has a balance function to equalize the voltages between the cells...then yes it would be suitable. If it only protects above 2.7V it's not what I am looking for.

Capacitors have a capacity. If they're showing different voltages at rest, they likely have different capacities and no amount of balancing is going to be helpful as the caps could potentially overwhelm any current the balancers can deliver.

On a completely unrelated note...

I see you're from the Netherlands... Your avatar is blue... Victron is based in the Netherlands... Victron is blue.

Anything we should know?

 

[Archerite]

Capacitors have a capacity. If they're showing different voltages at rest, they likely have different capacities and no amount of balancing is going to be helpful as the caps could potentially overwhelm any current the balancers can deliver.

I think the capacitor pack I bought that had voltage differences just have low quality caps or something. I have also been asking ChatGPT about this and it said something about causing a reverse voltage potentially harming a capacitor when it reaches 0.0V earlier than the others and when still being discharged.
By overwhelm you mean that they draw as much current as they possibly can right? That the balancers might be overloaded? Something like that?

I see you're from the Netherlands... Your avatar is blue... Victron is based in the Netherlands... Victron is blue.

Anything we should know?

Nice way of connecting the blue's there! ?If you're implying I might work for Victron then you're wrong though I am a big fan of Victron products obviously and most of my solar components are actually from Victron (SCC, SmartShunt, Orion DC-DC, Inverter's). Only my solar panels and wires and related stuff is just relativity cheap from amazon.

And my avatar is not even solar related, hahaha. It's commander shran from Star Trek Enterprise (actor: Jeffrey combs) It's also where my nickname is from. One particular episode he mentioned "Archerite" as a valuable mineral or something...and I was watching that episode while I was registering at another site (gaming related). So that's where that all comes from.

 

[sunshine_eggo]

I think the capacitor pack I bought that had voltage differences just have low quality caps or something. I have also been asking ChatGPT about this and it said something about causing a reverse voltage potentially harming a capacitor when it reaches 0.0V earlier than the others and when still being discharged.
By overwhelm you mean that they draw as much current as they possibly can right? That the balancers might be overloaded? Something like that?

What I'm saying is that you need a balancing current comparable to your load if your goal is to extract more capacity than the lowest capacity capacitor in the "battery" would provide.

A protection scheme is a far better approach. Once the lowest cap hits X Volts, cut off the discharge.

Nice way of connecting the blue's there! ?If you're implying I might work for Victron then you're wrong though I am a big fan of Victron products obviously and most of my solar components are from actually from Victron (SCC, SmartShunt, Orion DC-DC, Inverter's). Only my solar panels and wires and related stuff is just relativity cheap from amazon.

And my avatar is not even solar related, hahaha. It's commander shran from Star Trek Enterprise (actor: Jeffrey combs) It's also where my nickname is from. One perticular episode he mentioned "Archerite" as a valuable mineral or something...and I was watching that episode while I was registering at another site (gaming related). So that's where that all comes from.

?

 

[Archerite]

What I'm saying is that you need a balancing current comparable to your load if your goal is to extract more capacity than the lowest capacity capacitor in the "battery" would provide.

A protection scheme is a far better approach. Once the lowest cap hits X Volts, cut off the discharge.

Ahh, I see. I sort of low voltage cut off not for the whole pack but when one of the cells get's to low. I am still thinking a BMS is the way to go...but I want something cheap and if possible not reinvent the wheel. Also...considering my actual goals those low voltage situations might never happen. Using them as a buffer to smooth the voltage or capture from small generators.

There just is not enough capacity to use super capacitors as a sort of power bank. I do plan on using supercaps as a form of UPS for a small server I have running that uses just 5 watts.

Only my solar panels and wires and related stuff is just relativity cheap from amazon.

Actually...to clarify the implied "cheap wires" a bit....I have a mix of wires from amazon and a local victron focused shop! They sell high quality marine grade wires in a variety of gauges...but you do pay a premium for the quality. I did do that for the wires close to the battery where high currents are expected.
I also have a 20m run of 4mm2 that supplies a 24.5V line coming from a Victron orion DC-DC 12V->24V. That wire was not exactly cheap but I choose it because of the length and expected current 10-25A max (more like 2-6A in practice). And I have 4mm2 solar wire from offgridtec.

I also have a few cheap junk wires...even trashed a few of them because it was trash to begin with. Needs to be safe right?

 

[sunshine_eggo]

Ahh, I see. I sort of low voltage cut off not for the whole pack but when one of the cells get's to low. I am still thinking a BMS is the way to go...but I want something cheap and if possible not reinvent the wheel. Also...considering my actual goals those low voltage situations might never happen. Using them as a buffer to smooth the voltage or capture from small generators.

Yes. A BMS is the way to go. That's what they do. They monitor each cell and cut off the entire pack when any cell goes out of limits.. on the high side too.

 

[Archerite]

Yes. A BMS is the way to go. That's what they do. They monitor each cell and cut off the entire pack when any cell goes out of limits.. on the high side too.

I have found a local shop that sells various battery stuff and also BMS'es...so I placed an order there. I got a JK Smart Active Balance BMS BD4A17S4P which is supposed to support 8-17 cells, has bluetooth, can be configured for 1.2v-4.5v per cell, 40A max current. It was 45 euro's and should be delivered next day!



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