ronbot
1 mW
- Joined
- Apr 16, 2015
- Messages
- 10
How to start this...
I've had 25+ years in electronics design engineering, along with being a lifelong hobbyist. Rechargeable battery technologies has been a keen focus of mine for many of those years (along with alternative energy systems).
I'm in the middle of a personal Lithium conversion project (golf cart), and decided I didn't want to take the old "bulk charging / BMS balancing" route... I wanted better.
No... I actually wanted the best.
So I'm designing a modular system that (similar to what others have tried) utilizes a large 36-48V DC power supply (aka: "rectifier supply" as some are called for the telecom market) to provide input power. These are best purchased in the surplus market (such as eBay) to suit your local Mains grid. I could provide them, but for my 14p-16p project, I'm talking about a 1kW power supply, and they aren't cheap. (however, since these are totally isolated "per cell" modules, you could buy multiple smaller/cheaper power supplies to power them with, and just use as many as each of your 48V power supply will handle) This "Input Power Supply" could be left off of the vehicle, and connected using large Anderson PowerPole SBS connectors (or others of your choice).
My present design is fully protected for "walk away" confidence, and utilizes the following charge profile:
NOTES: "CC" = Constant Current charge rate = 10A for initial model (easily reduced)
. "CV" = Constant Voltage charge = 4.10V for the initial model
START CHARGE CYCLE:
1) Detect for over-discharged cell (<3.0V), if TRUE then proceed with "precharge" (slow charge @ CC/10) conditioning until cell > 3.0V
2) Charge at Full "CC" charge current, until "CV" cell Voltage is reached
3) Switch over to Constant Voltage (CV) charge mode
4) CV charge mode terminates when actual charge current drops to CC/10
5) End charge, until AC power is cycled
FEATURES:
ISOLATED... fully... in all regards.
Each and Every cell is ALWAYS balanced, and charged to the ideal voltage for long-life
Designed to be left connected to battery pack permanently, with leakage current of FAR less than 1mA per cell.
Each module is DC-Input fuse protected.
Each module has input power Reverse-Polarity Protection.
Each module is expected to have 90% efficiency, so very little power (heat) will be dissipated.
Each module is expected to be about 2" x 3"
Each module will have on-board status LED's
I'm still fairly early into this... but each "module" is expected to be splash-proof (conformal coated, at least), and have 20A terminal barriers as Input/Output connections, with redundant connections on DC-IN and Battery-Out. I'm also planning on an "open-collector" status output, so that every module can be "daisy-chain" inter-connected and give an "All Cells Charged" indication via a single remote LED.
Obviously a LiFePo4 version would also be needed, but my initial personal project is using Leaf battery packs, ergo my choice of voltages.
I actually have some 2nd generation model ideas in the works as well... a 100% fully custom version that could reduce cost a fair amount, as well as increase functionality and versatility (one size fits all)... but that is a topic for a later date... I have to get this one done first.
Shoot me some feedback!
How many cells do you need to charge?
What Chemistry?
What Charge Rate?
What price? (be realistic)
I realize that as DIYers, we're extremely sensitive to cost... and this 1st gen may be out of the reach of super cost sensitive projects... but for the functionality and ability to eliminate a costly Balancing BMS system, it's worth thinking about what this would be worth to you... on a "per-cell" cost. This will help me determine if it's even feasible for me to try to produce them in quantity for sale... or just for myself. I have PC boards to get designed and made, many parts to order, but I'm moving ahead with mine anyway.
$30/cell?
$40/cell?
$50/cell?
or?
Even if you're not in the market for such right now, I'd appreciate your input!
Ron
edit 4/29/15
Adding another simple but very useful feature... possibly even two...
(As I said, I'm still in the design process, determining what I want, and what others might want as well.)
Cell low voltage detector(s)
1) Cell DEAD: When the cell drops to 3.2V (probably adjustable) it will pull an Open Collector output "Low'. It's meant as a "last line of defense" to protect the cells. This will allow the cell to immediately enter the CC phase of recharge, versus waiting for the CC/10 slow charge. This output, when "Wire-OR'ed" (summed) with all other Cell Charger modules, will be used to drive the coil of a relay that will disable the Motor controller.
On the cell-charger PC Boards there will be another status LED that is lit when the battery voltage is above the threshold, and extinguishes when it's below that point. This will give "eyes-on" way to determine "which cell is it that just caused my vehicle to stop running", if you waited too long.
(If you really want to know the SOC condition of each cell, use a battery monitor. Many people won't need/want to know the cell condition, but only to protect them from damage.)
2) Cell "almost dead": See above, but the voltage is set a little higher... (probably about 3.60V for me). Also an Open-Collector output, but for another "dash mounted" LED. It's conceivable this could be utilized to enable a "low power mode" in a motor controller, to extend the last few miles... if the operator can't figure that out. Will also likely have an LED on-board for this as well... it's good for quick diagnostics if you don't have a BMS.
These are simple things to add-in, and even with the additional cost for each module, it's still far less than a BMS, and gives the essential protection functions.
I've had 25+ years in electronics design engineering, along with being a lifelong hobbyist. Rechargeable battery technologies has been a keen focus of mine for many of those years (along with alternative energy systems).
I'm in the middle of a personal Lithium conversion project (golf cart), and decided I didn't want to take the old "bulk charging / BMS balancing" route... I wanted better.
No... I actually wanted the best.
So I'm designing a modular system that (similar to what others have tried) utilizes a large 36-48V DC power supply (aka: "rectifier supply" as some are called for the telecom market) to provide input power. These are best purchased in the surplus market (such as eBay) to suit your local Mains grid. I could provide them, but for my 14p-16p project, I'm talking about a 1kW power supply, and they aren't cheap. (however, since these are totally isolated "per cell" modules, you could buy multiple smaller/cheaper power supplies to power them with, and just use as many as each of your 48V power supply will handle) This "Input Power Supply" could be left off of the vehicle, and connected using large Anderson PowerPole SBS connectors (or others of your choice).
My present design is fully protected for "walk away" confidence, and utilizes the following charge profile:
NOTES: "CC" = Constant Current charge rate = 10A for initial model (easily reduced)
. "CV" = Constant Voltage charge = 4.10V for the initial model
START CHARGE CYCLE:
1) Detect for over-discharged cell (<3.0V), if TRUE then proceed with "precharge" (slow charge @ CC/10) conditioning until cell > 3.0V
2) Charge at Full "CC" charge current, until "CV" cell Voltage is reached
3) Switch over to Constant Voltage (CV) charge mode
4) CV charge mode terminates when actual charge current drops to CC/10
5) End charge, until AC power is cycled
FEATURES:
ISOLATED... fully... in all regards.
Each and Every cell is ALWAYS balanced, and charged to the ideal voltage for long-life
Designed to be left connected to battery pack permanently, with leakage current of FAR less than 1mA per cell.
Each module is DC-Input fuse protected.
Each module has input power Reverse-Polarity Protection.
Each module is expected to have 90% efficiency, so very little power (heat) will be dissipated.
Each module is expected to be about 2" x 3"
Each module will have on-board status LED's
I'm still fairly early into this... but each "module" is expected to be splash-proof (conformal coated, at least), and have 20A terminal barriers as Input/Output connections, with redundant connections on DC-IN and Battery-Out. I'm also planning on an "open-collector" status output, so that every module can be "daisy-chain" inter-connected and give an "All Cells Charged" indication via a single remote LED.
Obviously a LiFePo4 version would also be needed, but my initial personal project is using Leaf battery packs, ergo my choice of voltages.
I actually have some 2nd generation model ideas in the works as well... a 100% fully custom version that could reduce cost a fair amount, as well as increase functionality and versatility (one size fits all)... but that is a topic for a later date... I have to get this one done first.
Shoot me some feedback!
How many cells do you need to charge?
What Chemistry?
What Charge Rate?
What price? (be realistic)
I realize that as DIYers, we're extremely sensitive to cost... and this 1st gen may be out of the reach of super cost sensitive projects... but for the functionality and ability to eliminate a costly Balancing BMS system, it's worth thinking about what this would be worth to you... on a "per-cell" cost. This will help me determine if it's even feasible for me to try to produce them in quantity for sale... or just for myself. I have PC boards to get designed and made, many parts to order, but I'm moving ahead with mine anyway.
$30/cell?
$40/cell?
$50/cell?
or?
Even if you're not in the market for such right now, I'd appreciate your input!
Ron
edit 4/29/15
Adding another simple but very useful feature... possibly even two...
(As I said, I'm still in the design process, determining what I want, and what others might want as well.)
Cell low voltage detector(s)
1) Cell DEAD: When the cell drops to 3.2V (probably adjustable) it will pull an Open Collector output "Low'. It's meant as a "last line of defense" to protect the cells. This will allow the cell to immediately enter the CC phase of recharge, versus waiting for the CC/10 slow charge. This output, when "Wire-OR'ed" (summed) with all other Cell Charger modules, will be used to drive the coil of a relay that will disable the Motor controller.
On the cell-charger PC Boards there will be another status LED that is lit when the battery voltage is above the threshold, and extinguishes when it's below that point. This will give "eyes-on" way to determine "which cell is it that just caused my vehicle to stop running", if you waited too long.
(If you really want to know the SOC condition of each cell, use a battery monitor. Many people won't need/want to know the cell condition, but only to protect them from damage.)
2) Cell "almost dead": See above, but the voltage is set a little higher... (probably about 3.60V for me). Also an Open-Collector output, but for another "dash mounted" LED. It's conceivable this could be utilized to enable a "low power mode" in a motor controller, to extend the last few miles... if the operator can't figure that out. Will also likely have an LED on-board for this as well... it's good for quick diagnostics if you don't have a BMS.
These are simple things to add-in, and even with the additional cost for each module, it's still far less than a BMS, and gives the essential protection functions.