DIY Programmable BMS (now using ATtiny/Arduino)

Batteries, Chargers, and Battery Management Systems.
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parabellum   10 MW

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Re: DIY Modular BMS

Post by parabellum » Apr 28 2013 2:43pm

chroot wrote:I would suggest you set 3V as last Modular BMS LVC tripping and secondary LVC tripping set 3.5V by Cyclist Analyst. That's what I am using it and never had any issue or problem with my LiPo battery pack. I am using Methods LVC modules (typically 3V for cutoff) in case you want know.
I agree.
dmwahl wrote:After I'm confident everything is working properly, I'll figure out what different voltage setpoints people are interested in and built the boards accordingly.
My vote is for LVC somwhere 3V to 3.3V and HVC 4.1V ( <4.15V aceptable)

Edit: For LiPo

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Re: DIY Modular BMS

Post by dmwahl » Apr 29 2013 1:56pm

Quick update... PCBs are on the way. They should arrive by the end of the week and I'll build them up and start testing as soon as I can.

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Re: DIY Modular BMS

Post by rf » Apr 30 2013 12:11am

Nice work!
dmwahl wrote: ... LVC is a voltage supervisor chip. They come in 0.1V increments from 0.9V up to around 5V, so LVC can be set to anything in between assuming the parts are available.
Voltage references engraved in silicon are great for easy accuracy on large production runs. Not always the best for smaller runs where levels can change.

It would be nice to switch between Lipo and Lifepo without doing surgery on boards, beyond a jumper or so.


Richard

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Re: DIY Modular BMS

Post by dmwahl » Apr 30 2013 9:09am

rf wrote:It would be nice to switch between Lipo and Lifepo without doing surgery on boards, beyond a jumper or so.
Agreed. I've been thinking of ways to do this, the easiest way would probably be to add a resistor to the divider network with a jumper to shunt it out. For now it will have to wait, but it's definitely a possibility for the future. I wonder how many people would take advantage of this?

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parabellum   10 MW

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Re: DIY Modular BMS

Post by parabellum » Apr 30 2013 9:23am

dmwahl wrote:
rf wrote:It would be nice to switch between Lipo and Lifepo without doing surgery on boards, beyond a jumper or so.
Agreed. I've been thinking of ways to do this, the easiest way would probably be to add a resistor to the divider network with a jumper to shunt it out. For now it will have to wait, but it's definitely a possibility for the future. I wonder how many people would take advantage of this?
Depends, what will be the price difference! Remember, it also makes it easier for you. :)

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Re: DIY Modular BMS

Post by dmwahl » Apr 30 2013 9:49am

parabellum wrote:
dmwahl wrote:
rf wrote:It would be nice to switch between Lipo and Lifepo without doing surgery on boards, beyond a jumper or so.
Agreed. I've been thinking of ways to do this, the easiest way would probably be to add a resistor to the divider network with a jumper to shunt it out. For now it will have to wait, but it's definitely a possibility for the future. I wonder how many people would take advantage of this?
Depends, what will be the price difference! Remember, it also makes it easier for you. :)
Price difference would be low, if any. Resistors are cheap and the cost of these will largely be driven by the non-passive components, PCBs, and assembly time. The "easier for me" factor would almost certainly outweigh the additional BOM cost. The main issue would be fitting jumpers onto the board, they're relatively large compared to the rest of the parts. I'll add it to the list of possible changes.

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Re: DIY Modular BMS

Post by mwkeefer » May 01 2013 11:48pm

While 3v is the "cutout" of the chemistry, i find 3.3-3.5 more prone to pack longevity... you may want to offer multiple cutoff versions, its just the resistor per channel difference right?

-Mike
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Re: DIY Modular BMS

Post by dmwahl » May 02 2013 8:25am

mwkeefer wrote:While 3v is the "cutout" of the chemistry, i find 3.3-3.5 more prone to pack longevity... you may want to offer multiple cutoff versions, its just the resistor per channel difference right?

-Mike
LVC is set by a fixed voltage monitor, they come in 0.1V increments so setting the LVC point is just a component change. For LiFePO4 I set the LVC point at 2.5V initially, the lost capacity compared to 2.0V LVC is only about 5-10% of the total, and I'd rather treat it gently than squeeze out all the possible charge.

PCBs came in last night, I'm going to build them up tonight. I've been experimenting with reflow soldering on the stove top and been getting much better results than I thought I would. You can hardly tell the difference between my results and boards that came out of a real reflow oven. I plan on taking a video of it, I'll post a link here when I have it uploaded.

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Re: DIY Modular BMS

Post by cassschr1 » May 02 2013 12:09pm

You had asked about charging amperage a while back. Possibly as high as 30a with a meanwell RSP-1500-48.

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Re: DIY Modular BMS

Post by dmwahl » May 02 2013 12:20pm

cassschr1 wrote:You had asked about charging amperage a while back. Possibly as high as 30a with a meanwell RSP-1500-48.
30A would be too high for my charge control board. The 4 cell modules would be fine, although you would run the risk of overrunning the shunts and overcharging the cells.

Why so high charge current?

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parabellum   10 MW

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Re: DIY Modular BMS

Post by parabellum » May 02 2013 12:26pm

dmwahl wrote:
cassschr1 wrote:You had asked about charging amperage a while back. Possibly as high as 30a with a meanwell RSP-1500-48.
30A would be too high for my charge control board. The 4 cell modules would be fine, although you would run the risk of overrunning the shunts and overcharging the cells.

Why so high charge current?
Isn't it just PWMing first and then shutting down at certain cell voltage (determined by 4s module)?

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Re: DIY Modular BMS

Post by dmwahl » May 02 2013 12:33pm

parabellum wrote:Isn't it just PWMing first and then shutting down at certain cell voltage (determined by 4s module)?
Not exactly, it allows full charge current until any cell reaches the HVC point, at which point the PWM circuit turns on to prevent the charger from overrunning the balancing shunts.

Once I have it built up and connected to my pack I'll take a video to show it in operation.

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Re: DIY Modular BMS

Post by dmwahl » May 03 2013 2:04pm

Got one of the boards soldered and tested last night, works great. Hand placing surface mount parts takes some time though, mostly applying the solder paste. I'm going to try etching my own solder stencil tonight, similar to what Felix explains how to do on lowpowerlab.com. A few of the boards also had exposed copper floods, so I'm going to increase the clearance for the next run. Fortunately it didn't cause any shorts, but I'd rather not run the risk in the future.

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Re: DIY Modular BMS

Post by rf » May 06 2013 3:03pm

dmwahl wrote:Got one of the boards soldered and tested last night, works great. Hand placing surface mount parts takes some time though, mostly applying the solder paste. I'm going to try etching my own solder stencil tonight, similar to what Felix explains how to do on lowpowerlab.com. A few of the boards also had exposed copper floods, so I'm going to increase the clearance for the next run. Fortunately it didn't cause any shorts, but I'd rather not run the risk in the future.
Where are the photos? We need our BMS porn!

:-)

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Re: DIY Modular BMS

Post by dmwahl » May 06 2013 3:28pm

Sorry :) Here you go. The first is etching a solder stencil to apply paste to the boards and the second is after reflow. There is definitely some improvement to be made, although minor. I'm going to replace the 1k resistors with an array and increase the flood clearance around components so that I don't have exposed planes. One of the boards from OSHpark had an exposed plane around a part, despite giving it 10 mils of clearance instead of the required 6 mils. I'll keep that one for my own experimentation, probably use it to build a UPS pack to replace the dead lead acid battery it came with.
IMG_0844.JPG
Stencil being etched
IMG_0844.JPG (234.98 KiB) Viewed 2347 times
IMG_0848.JPG
Freshly reflowed boards
IMG_0848.JPG (204.03 KiB) Viewed 2347 times

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Re: DIY Modular BMS

Post by dmwahl » May 06 2013 4:05pm

Also, I know the question "When can I get one?" will come up sooner or later... I set up a website to sell them through to keep track of stock, plus post schematics and other relevant info. I will post a link once I'm satisfied everything works as planned. People will be able to pre-order or wait until they are available.

I am also planning on making a through hole version available as a bare PCB, the circuit is the same, just using through hole parts so that people can put them together themselves. I prefer surface mount parts myself because they're much smaller (space efficient), but for the same reason I know they can be a pain to work with.

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Re: DIY Modular BMS

Post by chroot » May 06 2013 5:23pm

I would buy some LVC boards complete assembled and I wanted to see hows in action by getting LiPo battery low voltage hitting 3V or pre-adjust set specific voltage that will tripping cut off on the video or youtube.
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Re: DIY Modular BMS

Post by dmwahl » May 07 2013 11:18am

chroot wrote:...I wanted to see hows in action by getting LiPo battery low voltage hitting 3V or pre-adjust set specific voltage that will tripping cut off on the video or youtube.
I'll do my best to accommodate that, it may be a little tricky to get a video that shows it since the LVC cutoff ties into one of the controller's brake inputs. What exactly do you want to see?

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Re: DIY Modular BMS

Post by chroot » May 07 2013 11:49am

maybe i'll take a guinea pig and test it by getting lipo battery pack down to 3V if it trigger the cutoff or not.

Currently, I am running Methods LVC boards this time and the lvc board gives me 4p (20Ah) per pack and I wanted to know if your lvc board can do 4p hook up?
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parabellum   10 MW

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Re: DIY Modular BMS

Post by parabellum » May 07 2013 12:03pm

chroot wrote:maybe i'll take a guinea pig and test it by getting lipo battery pack down to 3V if it trigger the cutoff or not.

Currently, I am running Methods LVC boards this time and the lvc board gives me 4p (20Ah) per pack and I wanted to know if your lvc board can do 4p hook up?
Is there any difference for LVC in 3V on 5A series and 3v on 500A series?

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Re: DIY Modular BMS

Post by chroot » May 07 2013 12:20pm

No one will run 500A maybe Doctorbass or Luke's deathbike?

Anyways, with Methods LVC board should be same as DIY modular BMS when one of cell or a weak cell sagging or dropping reach 3V and it will trigger cut off instantaneous.

@dmwahl - How do you hook up BMS series in 20S4P that's why I am asking you for video how to do proper assemble with DIY modular bms.
parabellum wrote: Is there any difference for LVC in 3V on 5A series and 3v on 500A series?
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Re: DIY Modular BMS

Post by dmwahl » May 07 2013 3:12pm

chroot wrote:@dmwahl - How do you hook up BMS series in 20S4P that's why I am asking you for video how to do proper assemble with DIY modular bms.
Same as 20S1P. Since each 4P block is effectively one cell the hook up procedure doesn't change.

Each module has pins C1-, C1+, C2+, C3+, C4+ (see the image on page 3 of this thread). C1- goes to the negative terminal of the most negative cell, C1+ to the same cell's positive terminal, and so on.

I will make instructions as well as the schematic available before selling any of these, so you'll have everything you need to hook them up and then some. I'm in the process of hooking up the prototypes right now, and it's just a matter of connecting wires between the BMS and the pack. I happen to be soldering them to the BMS, but you can also use a female 4S JST-XH cable (such as http://www.hobbyking.com/hobbyking/stor ... duct=10802) to allow disconnecting the BMS easily.

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Re: DIY Modular BMS

Post by chroot » May 07 2013 3:15pm

Gotcha, Looking forward see your assemble before I buy your DIY modular BMS. I still read in 3rd page as you refer and trying open the picture in my mind to see how assemble with the balance leads.
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Re: DIY Modular BMS

Post by dmwahl » May 07 2013 3:20pm

chroot wrote:Gotcha, Looking forward see your assemble before I buy your DIY modular BMS. I still read in 3rd page as you refer and trying open the picture in my mind to see how assemble with the balance leads.
I'll take a picture tonight and post it here to give you an idea of what it looks like assembled.

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Re: DIY Modular BMS

Post by chroot » May 07 2013 3:27pm

I think you was refer to 2nd page (viewtopic.php?p=723303#p723303) and 20S bms is longer board than 4S BMS board size. I got it clear picture and sorry for the confusion. :D :thumbup:
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