Lowest Battery Voltage Monitor

[Electricdirtbiker]

Does anyone know a circuit that will monitor all the cells in a battery string and displays the cell with the lowest voltage? LVC alarms and shut off could be added later. The weakest or defective cell is a battery's limitation. An option also is to switch the circuit and monitor the cell with the highest voltage, for bulk charging shut off. The only way I can think of is by using a microprocessor.

Any ideas, thanks.

 

[AndyH]

One easy way is to use the LVC circuit from the Fechter/Goodrum BMS without connecting the opto outputs. Each LVC opto could be used to switch an LED which displays when that cell hits LVC. One could use a couple of different TC54s per cell (or per parallel group) to signal progress toward LVC. For example - use a red LED for 2.1V and a yellow for 2.6V.

 

[frodus]

There's a company in PDX I know of that is working on a 24-cell version of this, its in test right now. Its uC controlled. Monitors all channels independantly and its fully programmable. I think there are some GPIO on it too... I need to get back in there to see what its status is.

I think the only real way to do it is with a uC.... since you need to monitor an analog value for each battery and then chose what to do with the lowest/highest. Do you need to output to an LCD, or is it standalone?

 

[Electricdirtbiker]

Thanks for the responses.
I would mount this on to the bike somewhere. I don't have a good understanding of micro C's, so i was hoping to build one from discret componets. AndyH's idea with the voltage detectors could work. I would need as many v detectors as I want resolution per cell monitored, and a led for each. I could monitor them all at one glance. I'll check Mouser for v detector increments to see if they fall in the range I need. This is for a123 cell voltages.

Thanks again, Wesley

 

[Electricdirtbiker]

Frodus,
I was really looking for a direct reading voltage display and maybe a led to indicate what number cell is being monitored. Much eaiser to hope for than to design.

Thanks,
Wesley

 

[frodus]

you still need to monitor all nodes of the series pack... then you just program a small LCD to display the analog voltage and under neath it, read out the CELL number.

 

[AndyH]

Frodus,
I was really looking for a direct reading voltage display and maybe a led to indicate what number cell is being monitored. Much eaiser to hope for than to design.

Thanks,
Wesley

http://www.paktrakr.com/

uC device, LCD display, shows full pack status as well as graph and digits for cells. State of charge/fuel gauge, optional current sensor, etc. I'm using one with a scooter running 21 60Ah Thunder Sky cells. The PakTrakr is not a BMS but does provide a way to monitor and log pack data.

 

[MitchJi]

Hi,

These sound great and the price is great:
http://endless-sphere.com/forums/viewtopic.php?f=14&t=9229&start=0

Best damn 6S lithium monitor on the planet for $15

I have been holding out on posting about these for several months
I was hacking into them building a BMS for my 24S Lipo packs
Now that I have switched gears to a non-hub 12S setup I dumped that project.

Well here they are:
http://cgi.ebay.com/Chargery-BM6-2S...5|66:2|65:12|39:1|240:1318|301:0|293:1|294:50

http://www.chargery.com/cellMonitor.asp

Works for both Lipo and Lifepo4
$15
Reads 6S lipo via 0.100 spacing (perfect for JST-XH balancer plugs)
5mV accuracy - most balancers quit at 20mV
Shows you 8 things in sequence:

Total Pack Voltage
Largest Imbalance
Cell voltages for 1 to 6 (or however many you hook up)

The monitor beeps if you go under 3.0V or over 4.22V
EDIT: I forgot, you can set the LVC to any desired voltage.

Absolutely dead on voltage.
AWESOME product. Works perfectly every time.
I have been running 4 of them for several months on my big Lipo packs and they have saved my ass!

Let me say this... Anyone who goes to "Full Pack LVC" on a lipo pack is retarded to some degree. . . If the total pack has reached LVC then it is absolutely certain that at least a few of the cells are way under 3.0V.

LVC must always be handled on a cell level basis like is done with the 24 channel BMS.

If you plug these into your lipo packs then you will hear a loud BEEP BEEP BEEP any time one of your cells drops below LVC. I think you will be surprised about what happens under load :wink:

Anyone who is a nOOb getting into Lipo MUST own one of these.
Will save your butt while charging, discharging, and comes in damn handy for checking out cells.

The beeper output can drive an optocoupler that can be used to TAP TAP TAP your ebrake when you hit LVC
Does not cut you off, just gives you a warning...

...P.S. Using two BM6's for a 12S pack works well. The only thing you lose is the ability to see the Max Delta. The alarm feature still works exactly the same.

 

[methods]

I second my post above.
Buy as many of those as you need and use the beeper output to trigger whatever you want to trigger.

-methods

 

[Electricdirtbiker]

The Chargery monitor sounds great. Can it be used with a123 voltages? 2.7 v lvc and 3.6v for ov.
Thanks
Wesley

 

[MitchJi]

Hi,

The Chargery monitor sounds great. Can it be used with a123 voltages? 2.7 v lvc and 3.6v for ov.
Thanks
Wesley

EDIT: I forgot, you can set the LVC to any desired voltage.

 

[Electricdirtbiker]

Chargery's website indicates that the B6 will display a cell voltage between 3.0-4.2v. And elsewhere the alarm can be set as low as 2.0 v. If I program it for an alarm voltage of 2.7v. Does this mean the B6 display goes blank below 3.0v, but the alarm will still sound at 2.7v?
Also is the over voltage programable from the 4.2v down to 3.6v?
Thanks, Wesley

 

[methods]

Cell Voltage display range: 1.50-4.99V
So no the display will not go blank. The cell voltages will be displayed down to 1.5V

Total Voltage display range : 3.00 ~29.94V
This refers to the reading of the entire pack
The lowest entire pack voltage is 3.0V

As far as alarms: I know how to set the LVC but I dont think you can change the HVC alarm. It is possible that the HVC alarm drops with the LVC setting, not sure.

I dont really use the HVC all that much anymore.
I balance while charging and monitor while discharging.

I have found that if you leave them plugged in for a week they will start to put the pack out of balance.

-methods

 

[Electricdirtbiker]

Methods,

This is sounding more like what I've been looking for.
I'm running a 16 cell series pack, so I will need 3 B6's. If I'm not riding for a while, to prevent discharge, should I unplug the B6's, or is there a way to power off by switch? The B6's must have at least 7 wires each, not so easy to switch, maybe just every other wire.
When the B6's are powered on, do they need to be reprogramed each time, or do they hold memory?
When the lvc alarms, does the B6 display which cell?
For me the HVC would be useful only for bulk charging. Nice to have.
I'll be charging and balancing each cell with its own charger.
What type of cells are you using?

Thanks
Wesley

 

[tostino]

Oh my god, I really wish they had a 7s version of that. Do any of you know of one? after I saw that post, I went searching for quite a while, but 6s is all I found so far.

If not, I can just use two of them!

 

[methods]

Methods,

This is sounding more like what I've been looking for.
I'm running a 16 cell series pack, so I will need 3 B6's. If I'm not riding for a while, to prevent discharge, should I unplug the B6's, or is there a way to power off by switch? The B6's must have at least 7 wires each, not so easy to switch, maybe just every other wire.

You should unplug them.
I imagine that if you put a switch on the ground of the lowest cell it would shut down.
Have to try it to find out.

When the B6's are powered on, do they need to be reprogramed each time, or do they hold memory?
When the lvc alarms, does the B6 display which cell?
For me the HVC would be useful only for bulk charging. Nice to have.
I'll be charging and balancing each cell with its own charger.

They hold memory
I think the display continues to revolve around and the alarm sounds when it gets to any cell that is below LVC.
It cant stop on the lowest because there could be multiple low cells.
You can tell which cell or cells are lowest by reading them off as it goes around.

Watch out using a balancer with this at the same time. It can affect the balancer a little. I have some balancers that behave identically with or without the BM6. I have others that behave in an odd way that I cant describe.

What type of cells are you using?

Thanks
Wesley

I am using Lipo cells so I use LVC 3.0V and HVC 4.2V
24S 2P 10A 88.8V pack so I use 4 of these

-methods

 

[methods]

Oh my god, I really wish they had a 7s version of that. Do any of you know of one? after I saw that post, I went searching for quite a while, but 6s is all I found so far.

If not, I can just use two of them!

You will never find a 7S version.
There are some 8S and 10S chargers but the industry standard is 6S and 12S

You should use 2 of them.
They will auto-detect the number of cells.

-methods