Low cost BMS - Page 9 - Fuel Economy, Hypermiling, EcoModding News and Forum

harlequin2 · 02-17-2013, 04:47 PM

Jumpers are not "delicate" at all and can work very well in this sort of application.
I've done a lot of work with networking systems for various applications and addressing has always been a bugbear. If you have a few hundred nodes and they all have to be set up individually, it becomes a real PITA. Hence my daisy chain system where its all taken care of automatically! I can't think of a better way to do it and I look forward to the day that someone shows me such a thing.

filip · 02-17-2013, 04:52 PM

Quote:

Originally Posted by harlequin2

I've done a lot of work with networking systems for various applications and addressing has always been a bugbear. If you have a few hundred nodes and they all have to be set up individually, it becomes a real PITA. Hence my daisy chain system where its all taken care of automatically! I can't think of a better way to do it and I look forward to the day that someone shows me such a thing.

I will try to play with the IR broadcasting solution and provide some feedback on advantages/disadvantages.

Each module needs a bench test after assembly and it seems to me that setting the address after verifying the MCU operation won't be that troublesome.

kovgab3 · 02-23-2013, 11:34 AM

Quote:

Originally Posted by harlequin2

First off, you can't use a fet as a load without some form of stabilisation - simply applying some voltage to the gate results in a completely unknown and quite unstable current flowing. "Calibration" as you suggested does not work, it is simply too unstable to be even thought about.

Many "commercial" BMS cell modules are using FETs for dissipating.
They don't measure the dissipating current, but they are monitoring the temperature of the FET.
And they use PWM to keep the FET living

for example:

kovgab3 · 02-23-2013, 11:34 AM

doesn't let me attach a link...

kovgab3 · 02-23-2013, 11:35 AM

maybe after 2 more posts...

kovgab3 · 02-23-2013, 11:36 AM

last empty post... sorry for that

kovgab3 · 02-23-2013, 11:37 AM

maybe now:
EV-Power | RT-BMS System

harlequin2 · 02-23-2013, 04:23 PM

Yes, that could work. You'd need a choke in series with the fet to limit the rate of rise of current - you'd effectively be making a switch-mode power supply! Also, a temperature sensor on the fet. Is that simpler than a current sensor? And why use a fet? A bipolar transistor might be better as its easier to drive from a logic level.
So there you go: A pwm drive output from the micro, a bipolar power transistor, a choke and a small resistor in the emitter lead of the transistor to act as a current sensor feeding into a spare adc input on the micro. The transistor is turned on and the current monitored - transistor turned off when I reaches the desired level. Oh, you'd need a Schottky diode across it as well to absorb the voltage spike when the transistor turns off.
All this to shift the heat dissipation from a resistor to a transistor.
If anyone can think of a clever way of sending this power to the cell with the lowest voltage, you might have something.

kovgab3 · 02-24-2013, 05:15 PM

Quote:

Originally Posted by harlequin2

All this to shift the heat dissipation from a resistor to a transistor.

Not "ONLY" for that.
But to raise the dissipating current in a quite cheap way.
As you also had written some posts before, if you want to dissipate with 5A, then you need a large and expensive high power resistor. And it's very difficult to remove the heat that gets generated there.
If you use a resistor with metal housing, that will be even much more expensive, and that's a pain to assembly onto a heatsink.

If you use a "cheap" FET, then the heatsink is easy to attach. If you monitor the temp. of the FET, and you play with the PWM of the FET (and the current through on that), then the FET lives long, and dissipates much more current, then the resistor.