DIY Pack Monitor and alarm.

[Jermo]

I was thinking about pack monitors and looking at battery performance curves. It occurred to me most monitors are watching the wrong things. battery voltage is very slight and isn't a good indication of capacity taken from a pack.

The concept here is to measure and track mAh pulled from the pack and alert at a certain point. The other thing would be to monitor individual cell voltages to ensure none went below a specified level (safety of the pack).

I had thought about current loops but to my knowledge they only operate with AC. The other thought was to use a hall effect transistor. Anyone have other ideas/concepts along these lines or suggestions on how we might monitor and quantify mAh over time? I want to avoid using a shunt if I can due to power losses but that might end up as the cost effective method.

[th3tick]

Having just pulled 1969mAh from my brand new Flight Power 2170 pack, with that still registering 10.2 volts after flight, I had similar thoughts about monitors. Sadly, I don't have the right knowledge to help, other than agree...

John

[Probedude]

The other thought was to use a hall effect transistor.
Here's a link to a hall sensor + conditioning ckt + current sense conductor all in one package.
http://www.allegromicro.com/en/Products/Part_Numbers/0752/index.asp
Newark has some stock, 100A version for $6.07 in singles.

This might even be the part Eagletree is using in their datalogger.

Dave

[Jermo]

mmm...DA converter, counter circuit and a timer, mmm...small pic with Flash for configuration... I'm seeing definately possibilities...

[kgfly]

Go for it Jermo :wink:

[Jermo]

As soon as I get back to work I'll order one of the devices to prototype. I need to do some research on controllers because most have everything else we'd want built in. I just have to find one I like. I don't have any programming gear (sold it all off a few years back) but that should be easy to get.

So far the method of operation is all too simple.
1. Program a threshold value - likely using beeps for each digit. This gets converted to binary.
2. The Analog to Digital converter samples the output of the transducer x times per second into a summation with a stored result. every y cycles of x, shift result by x and subtract the result from the threshold. (might be faster to just sum the result over time and compare it to the threshhold.
3. when the comparison value exceeds the threshold (another bit is used) output alarm..ie buzzer, lamps, ....etc.

Depending on the microcontroller/pic used this thing could eventually become alot more. I'll resist expanding it until we end up with a working proto.

[kgfly]

The ideal alarm needs to monitor voltage and current to protect against those times when a partially discharged battery is connected up. Monitoring individual cells could get messy, but I suggest designing the v1.0 circuit to at least allow for measuring both the current and the overall pack voltage.

I guess the unit will be powered directly from the main pack (like all the FDRs are) so you have to consider the range of supply voltages and design your onboard regulator and Vref with that in mind. Be nice if the unit can operate from 2S to 12S (6V to 50V).

Great idea Jermo, looking forward to following your progress.

[Probedude]

I need to do some research on controllers because most have everything else we'd want built in. I just have to find one I like. I don't have any programming gear (sold it all off a few years back) but that should be easy to get.

I vote for having a serial port and just program it on your PC. You can do so much more with a GUI to let you enter parameters, have the PC bracket/check the data, even do any 'hard' math to come up with the register values to program into the heli watchdog unit. Also use the serial port to download information from the watchdog unit. I'm pretty sure this is why the EagleTree unit is 'so sophisticated'. All it is doing is logging A-D values from the current sensor, and any other sensor that is spitting out a voltage or frequency, over time - time just being clock cycles on the CPU. The PC software then does the conversion to actual volts, amps, rpm, etc.

Regarding programming pics, they all support serial programming these days and support in-circuit programming. Not much to buy and you can make your own programmer, and of course MPLAB is free. Take a look at the Atmel line of microcontrollers too. They have a nice assortment of 'features' for cheap and in combinations not available in the PIC lineup.

KGfly - the unit will consume little power so being able to be powered by that wide voltage range is easy. The thing to watch out for is common mode voltage issues, spikes, and signal conditioning.

Dave
Heli/Lipo Watchdog - 05-16-2007 (just in case someone else is hoping to use the name!)

[Jermo]

very true..and we get the advantage of updating via firmware. It's just been a long time since I've done this. I'm sure they don't use assembly anymore :D .

Supply voltage isn't a concern since most of the stuff I recall working with had a large working voltage range. The total pack voltage would be easy to monitor since it's all available on the same connections if we use the balance connector. The part that I'm not sure of yet is the ADC connections since we need to ideally support 1s up to 12s?.

as a side note this circuit would be able to record current use just like the eagle since the data is right there already.

I can't promise to make this but I'll certain make the effort once I'm back to work.

[th3tick]

Would it make sense to do something which grafts on to the E-Logger itself? The Power Panel does something like this already, displaying it instead of setting off an alarm. That is, for the mAh counting at least.

[Jermo]

It wouldnt' take much to have an add on display. I'd prefer to have any diplay as an add on to cut weight. If you choose to fly with the display that's your call. In addition this would make it easy to mount the display anywhere.