thunderstorm80
1 kW
- Joined
- Mar 29, 2016
- Messages
- 383
Hi,
This post is a bit "steamy", so I warn you beforehand. It's just that I feel kind of hopeless, so I thought to ask the community, and I am almost 100% sure that someone on ES had the same needs and found a solution.
I am still using my A123 20Ah prismatic cells without BMS for 4 years by now. They still have almost the same capacity since I bought them second hand.
These are precious cells and I want to protect them from going outside their voltage limits. In those 4 years I had them manually balanced like once per year.
Once in a while I try to find a BMS for them for the day the first cell will age faster than the others, and without immediate action it would cascade a catastrophe.
Unlike controllers, batteries, motors, BMS is a total *shit* (sorry for the expression) to browse for information.
It's a jungle of chinese makers with BMS's where most of them will do more damage to your battery rather than protect it, open source projects (but where can I actually BUY them??), and in addition the LiFe chemistry has a special 3.3V and their huge sustainable 100A discharge / 80A charge rate. The search was doomed. I just gave up.
And yes, I can buy miniBMS. It's just that my wallet is not that deep, considering I have 24S battery on bike, 25S on another, 8S on another project, and so on...
So I thought, let's compromise. Let's take Arduino which has 6-8 analog inputs, and add an input extension shield like this one so I can read all 24 cells into the same Arduino board:
http://www.dadaelectronics.eu/shop/arduino/analog-input-extension-shield-for-arduino-r-ka12-kit
This is the only product I found that can just "multiplex" analog inputs and come with the proper libraries without being complicated as hell, and the only store which sell it (all other places said it's discontinued) ask ridiculous amount to ship it over here. I would pay that "premium" shipping price, but if all shops have that shield discontinued, maybe it's for a reason.
Anyhow, with such shield, I can monitor all 24 cells, and show the information about the voltages on a screen of my choice at real time. This will not have an LVC or HVC, but it can visually alert me or "siren" me to warn me when I approach the limits.
Why not have LVC and HVC? I will need to find a proper power mosfets for the currents, and wire everything myself considering I am not very good with designing circuits that involve transistors.
Oh well, you can use a relay, right? Nope, at 100A and 80V DC, those would be super expensive and HUGE.
And so I thought, are there "electronic" relays where a mosfet is replacing the actual actuator and it's driven by a simple control circuit for those of us who don't have an academic electronic degree from university?
And then I had another idea: I already had my circuit breakers protecting me when one of my controllers became a FULL short-circuit in the middle of a ride. Household circuit breakers are small, reliable, and cheap.
It could have been easily converted into a relay (half one, at least), if there was one that had a coil that can receive external current on the magnetic element and trip the connection at will. That external current would be delivered to that circuit breaker from the arduino via a conventional relay.
I then thought of a Residual current breaker, and perhaps they can actually be that "one direction relay" I am looking for?
You say I didn't look enough for BMS's? Well, I did. I even got one which is supposed to be for LiFe. The bastard let the cells "fry" to 3.8V before it agrees to cut them off! (3.6V is the HVC)
This is why I don't trust those factory made BMS's. They have no faithful documentation, if at all, and they can't be trusted when you depend on them.
This is why I recommend everyone to buy E-bike gear ONLY at Grin. Too bad they don't sell BMS's, but maybe for a reason...
Only Grin has faithful documentation and a strong-back for their products.
That is all...
Sorry for the length, but I hope you understand me.
I will be happy if you can point me for a solution with either of the options.
For example, if you have LiFe battery, a BMS which works, obey the special LVC/HVC of LiFe, and is reliable - I will be happy to hear about it.
Thanks.
This post is a bit "steamy", so I warn you beforehand. It's just that I feel kind of hopeless, so I thought to ask the community, and I am almost 100% sure that someone on ES had the same needs and found a solution.
I am still using my A123 20Ah prismatic cells without BMS for 4 years by now. They still have almost the same capacity since I bought them second hand.
These are precious cells and I want to protect them from going outside their voltage limits. In those 4 years I had them manually balanced like once per year.
Once in a while I try to find a BMS for them for the day the first cell will age faster than the others, and without immediate action it would cascade a catastrophe.
Unlike controllers, batteries, motors, BMS is a total *shit* (sorry for the expression) to browse for information.
It's a jungle of chinese makers with BMS's where most of them will do more damage to your battery rather than protect it, open source projects (but where can I actually BUY them??), and in addition the LiFe chemistry has a special 3.3V and their huge sustainable 100A discharge / 80A charge rate. The search was doomed. I just gave up.
And yes, I can buy miniBMS. It's just that my wallet is not that deep, considering I have 24S battery on bike, 25S on another, 8S on another project, and so on...
So I thought, let's compromise. Let's take Arduino which has 6-8 analog inputs, and add an input extension shield like this one so I can read all 24 cells into the same Arduino board:
http://www.dadaelectronics.eu/shop/arduino/analog-input-extension-shield-for-arduino-r-ka12-kit
This is the only product I found that can just "multiplex" analog inputs and come with the proper libraries without being complicated as hell, and the only store which sell it (all other places said it's discontinued) ask ridiculous amount to ship it over here. I would pay that "premium" shipping price, but if all shops have that shield discontinued, maybe it's for a reason.
Anyhow, with such shield, I can monitor all 24 cells, and show the information about the voltages on a screen of my choice at real time. This will not have an LVC or HVC, but it can visually alert me or "siren" me to warn me when I approach the limits.
Why not have LVC and HVC? I will need to find a proper power mosfets for the currents, and wire everything myself considering I am not very good with designing circuits that involve transistors.
Oh well, you can use a relay, right? Nope, at 100A and 80V DC, those would be super expensive and HUGE.
And so I thought, are there "electronic" relays where a mosfet is replacing the actual actuator and it's driven by a simple control circuit for those of us who don't have an academic electronic degree from university?
And then I had another idea: I already had my circuit breakers protecting me when one of my controllers became a FULL short-circuit in the middle of a ride. Household circuit breakers are small, reliable, and cheap.
It could have been easily converted into a relay (half one, at least), if there was one that had a coil that can receive external current on the magnetic element and trip the connection at will. That external current would be delivered to that circuit breaker from the arduino via a conventional relay.
I then thought of a Residual current breaker, and perhaps they can actually be that "one direction relay" I am looking for?
You say I didn't look enough for BMS's? Well, I did. I even got one which is supposed to be for LiFe. The bastard let the cells "fry" to 3.8V before it agrees to cut them off! (3.6V is the HVC)
This is why I don't trust those factory made BMS's. They have no faithful documentation, if at all, and they can't be trusted when you depend on them.
This is why I recommend everyone to buy E-bike gear ONLY at Grin. Too bad they don't sell BMS's, but maybe for a reason...
Only Grin has faithful documentation and a strong-back for their products.
That is all...
Sorry for the length, but I hope you understand me.
I will be happy if you can point me for a solution with either of the options.
For example, if you have LiFe battery, a BMS which works, obey the special LVC/HVC of LiFe, and is reliable - I will be happy to hear about it.
Thanks.