"Zephyr" - Finally, the "v4" Fechter/Goodrum/Hecker BMS...

do you think you could do that again with the camera focussed on the job and not swinging about as you change positions? It is very difficult to follow. That way we can see if the leds are coming on all at once or separately. and can you discahege the battery a bit first.
 
Gregb said:
do you think you could do that again with the camera focussed on the job and not swinging about as you change positions? It is very difficult to follow. That way we can see if the leds are coming on all at once or separately. and can you discahege the battery a bit first.

The leds all flash at the same time including the main led

I will try and post anothe video today woth battery discharged a bit first
 
I think i got it working, i tune the voltage of my psu so that each cell charges to 4.10v, the shunt channels dont even light up, but once the cells reach the 4.10v mark the led trips to green. It seems the channel shunt will only ever light if the cells are to out of balance.

i tried setting the charger so each cell gets up to 4.15v but it would not trip the main led to green, instead it would continously try to trip the main led with all shunts lit up but could not, i guess because the voltage was simply to high

Steveo
 
steveo said:
I think i got it working, i tune the voltage of my psu so that each cell charges to 4.10v, the shunt channels dont even light up, but once the cells reach the 4.10v mark the led trips to green. It seems the channel shunt will only ever light if the cells are to out of balance.

i tried setting the charger so each cell gets up to 4.15v but it would not trip the main led to green, instead it would continously try to trip the main led with all shunts lit up but could not, i guess because the voltage was simply to high

Steveo
I was grappling with this same problem for ages - trying to make it so that they all charge right up to the perfect voltage. But what I found was that you really have to dial down the voltage a bit before it reliably triggers the EOC.

It's never going to be absolutely perfect, but it's better to leave the charger voltage just a little short of the ideal cell voltage than risk the BMS cycle staying stuck on and gradually heating up. I've got my charger now at about 85.8V(3.58V per cell) rather than the ideal 86.4V (3.6V per cell). Most of the LEDs come on just ever-so dimly and BMS never gets hot. So far this seems to be doing the trick and my EOC is set so that it cuts out once the current drops to 1.0 amps. (from my charger's standard 9.0 amp charge rate). If I had the EOC any lower than this, it had a tendency to stay stuck on at around 0.8 amps and never switch to green at all.

I've still yet to give it a proper trial with these adjustments, the proof of the pudding to me will be if it reliably switches off in pulse mode, which I found was causing me the most difficulties with the EOC cutoff. Fingers crossed that this will behave better at the new voltage and EOC settings.
 
Lowering the charger voltage is a good workaround for now, but the circuit is supposed to still turn off at the right current even when it is cycling. I suceeded in creating a test fixture that duplicates the problem. Now I'll try to find a simple way to correct it. Hopefully it will just be a component value change somewhere.

The cycling mode is equivalent to the throttling on older versions of the board. I just slowed it way down to prevent charger interaction issues.
 
OK guys, got it.

The problem was with higher charge currents/smaller cells, the on time during cycling was too short for the EOC detector to trigger. In earlier testing, we were mostly using very large cells at a lower charge rate, so the timing was not an issue.

The solution will be to add a 1N914 diode to enable the EOC detector during the HVC delay time. My test setup used no cells (worst case) so the timing cycle was as short as possible.

The diode needs to go from the base of Q2 to U3 pin 7 or the gate of the main FET. The cathode (end with the black band) goes to Q2.

Here is a layout diagram showing the location of the diode (in blue). I think you can bend the legs of the diode around the existing resistor legs and solder it in.

The anode side of the diode can go to either end of R14.

Once you install the diode, you should be able to crank the charger voltage up a bit and still get good end of charge shutdown.
Some cycling is normal if there is significant cell imbalance, but it should shut down after a reasonable amount of time. Having the diode will make variations in charger voltage less critical.
 
fechter said:
OK guys, got it.

The problem was with higher charge currents/smaller cells, the on time during cycling was too short for the EOC detector to trigger. In earlier testing, we were mostly using very large cells at a lower charge rate, so the timing was not an issue.

The solution will be to add a 1N914 diode to enable the EOC detector during the HVC delay time. My test setup used no cells (worst case) so the timing cycle was as short as possible.

The diode needs to go from the base of Q2 to U3 pin 7 or the gate of the main FET. The cathode (end with the black band) goes to Q2.

Here is a layout diagram showing the location of the diode (in blue). I think you can bend the legs of the diode around the existing resistor legs and solder it in.

The anode side of the diode can go to either end of R14.

Once you install the diode, you should be able to crank the charger voltage up a bit and still get good end of charge shutdown.
Some cycling is normal if there is significant cell imbalance, but it should shut down after a reasonable amount of time. Having the diode will make variations in charger voltage less critical.

thanks for looking into this fechter, I will try this mod when i have the chance...

as i mentioned earlier i was able to set the charger so each cell his 4.10v and then the main led goes to green

with this mod, will it allow me to set the voltage of the cells to 4.15 of 4.20v for lipo?... any ideas roughly? how about for a life cells?

thanks
-steveo
 
I have asked this question on another thread to no avail and have tried finding it on the mouse catalogue.
Does anyone know the name /no. of the plug for the cell-log O/P plug and where it can be obtained?
thanks
Greg
 
steveo said:
thanks for looking into this fechter, I will try this mod when i have the chance...

as i mentioned earlier i was able to set the charger so each cell his 4.10v and then the main led goes to green

with this mod, will it allow me to set the voltage of the cells to 4.15 of 4.20v for lipo?... any ideas roughly? how about for a life cells?

thanks
-steveo

It won't change the voltage where the shunts come on but will allow a little more variation in charger voltage and still have a reliable shutoff. With the EOC pot turned up higher, you can run the charge current higher toward end of charge to speed things up.
 
Gregb said:
I have asked this question on another thread to no avail and have tried finding it on the mouse catalogue.
Does anyone know the name /no. of the plug for the cell-log O/P plug and where it can be obtained?
thanks
Greg

I've never been able to find them. If you find some, let us know. I wish they used a more common connector.
 
Thanks a lot! I'll get round to this soon...
Does this fix the EOC issue generally (it not shutting off in either mode with the voltage set too high), or just the pulse mode EOC issue? Is the 1N914 diode the "1N914_T50A" that is used elsewhere on the control circuit?

Thanks
 
Zenid said:
Thanks a lot! I'll get round to this soon...
Does this fix the EOC issue generally (it not shutting off in either mode with the voltage set too high), or just the pulse mode EOC issue? Is the 1N914 diode the "1N914_T50A" that is used elsewhere on the control circuit?

Thanks
Almost any diode will work. Yes, I used the same one used elsewhere on the board.

This will fix the problem where it goes into cycling and gets stuck in that mode.
If you set the charger voltage way too high, the shunts will be full on at end of charge and you would need to adjust the EOC pot higher than about half way to make sure it turns off, but it should still turn off.
 
I've done the mod. Since I had it open, I took it as an opportunity to fit the second Q3 FET, so that I can run it with a 15A or 20A charger later on.

I elected to mount the diode on the underside of the board. The diode leg had just enough room to fit in with the FET leg, which made it nice and straightforward to double up the two jobs.

[EDIT] Corrected as per Richard's suggestion in the following post. It goes to the gate not the source :oops:. I moved it across to the rail serving the gate (shown at the bottom of the picture).

The other end just went to the bottom of the middle pin of Q2.

gfmod02b-640x480.jpg

[EDIT] Photo of corrected layout as per Richard's suggestion

It'll be some time before I know for sure that this works. I'm still fine-tuning the charger voltage and EOC. It seems that unless I have it just a bit lower than the 86.4V ideal (3.6V per cell), then it sometimes sticks and never switches off. The voltage seems to fluctuate a little according to various factors, and if it goes over a certain threshold then it will just run away, never turning off and just getting hotter and hotter. It looks to me that - for whatever reason - a slightly lowered voltage is what my system is happiest with. All the cells end up nicely balanced once they've settled, and they all discharge in step with one another right up until they cliff-dive at the end.

I've set to see if this mod has fixed the pulse mode yet. One thing I did notice while tinkering, is that once I ramped up the voltage again, pulse mode came on by itself. Is this a good way of 'forcing' it to see if it works, and also calibrating the EOC with this mode?
 
I can see from the pic that the diode is going to the wrong leg on the FET. It should go to the gate leg, which has the skinny trace. It looks like maybe you can just snip one end off and move it over to on top of the trace leading to the gates.

Once you get that moved over, yes, you should be able to get it going in the throttling mode and dial up the pot and it should shut off. If you have a way to measure the current it may be helpful.

During normal operation, near end of charge you may or may not see it go into the throttling mode depending on how much imbalance there is in the cells. After that it should shut down. I think if you have the pot set high (more CW), it will shut down a bit early which may be better for the cells.
 
fechter said:
I can see from the pic that the diode is going to the wrong leg on the FET. It should go to the gate leg, which has the skinny trace. It looks like maybe you can just snip one end off and move it over to on top of the trace leading to the gates.
Doh! :oops: It was a long day...
gfmod02b-640x480.jpg


Thanks for the suggestion! Easy fix.
 
fechter said:
Once you get that moved over, yes, you should be able to get it going in the throttling mode and dial up the pot and it should shut off. If you have a way to measure the current it may be helpful.
Yes. The great thing about the BMSBattery charger is they have a display that is switchable between voltage and current. It's in my little video (25 seconds in) from when I first tested the board:
http://www.youtube.com/watch?v=QN6tYkzuMNM&feature=related

Now I've put the extra main MOSFET on, should I be okay with a 15A or 20A charger? I built it solidly with nice thick gauge wire everywhere. Are there any issues I should be aware of before I try it with anything more powerful (apart, of course, from making sure the EOC is stable and works okay now)?
 
Zenid said:
Now I've put the extra main MOSFET on, should I be okay with a 15A or 20A charger? I built it solidly with nice thick gauge wire everywhere. Are there any issues I should be aware of before I try it with anything more powerful (apart, of course, from making sure the EOC is stable and works okay now)?

Should be no problem. A single FET can handle up to about 20A. The current shunt will get hot, but it is made to take it. Just avoid having any wires in contact with it as the insulation could possilby melt.
 
Still not terribly impressed with the instructions. In the Charge Control section Test It says use a current limited PS set to 100mA but no mention of initial voltage. It then says turn voltage up to 20V... From what ???
There is still no instruction for 8 cell units that after cutting the board then term 9 or B8 should be strapped to +.
and it is as though the 47uF (c101) capacitor across the leads doesn't exist....
 
Gregb said:
Still not terribly impressed with the instructions. In the Charge Control section Test It says use a current limited PS set to 100mA but no mention of initial voltage. It then says turn voltage up to 20V... From what ???.
From zero would be a safe guess...

I didn't have any fancy equipment, so I used his alternative approach of simply running a power supply to it in series through a 100W bulb. That protects the board in case there are any shorts. You can test both the shunt circuits and the main control circuit that way. If you look earlier on in the thread, you can see where I'm running through the tests and double-checking with Richard (Fechter) if I'm doing it right, what to expect and what to do next.

I will get round to writing this up at some point, but I've been busy with other things. If you don't have bench power supply equipment, just run a charger through a 100W light-bulb. Use a little screw-in light-bulb holder, and run the positive through the bulb and use the wire that comes out of it as your "protected" power source to attach to the positive of the board, to check that the main LED lights and that shorting the EOC pins turns the LED red. If something is badly wrong with the board then the bulb will light up brightly.
 
Yes I have been collating all your chats about testing. It is just that the tests and instructions seem to be written for advanced users and not people like yourself, new to the game. The charging or discharging of the 47uF could be confusing to people trying to measure/compare the chan leads. And the other things I have listed should have been included by now. There is serious money involved in building this. Also many bench supplies don't like being started at zero. I have written quite a few instructions for techs over the years and these are not among the best I have read. There doesn't seem to be a consolidated list of corrections yet or the differences of the various marks of boards. Especially the addition of the switching diode. And Gary's web page is still down. I have been caught up with a lot of other things recently including making a bench PS so have put it aside for the time being and just read the thread when I can. Don't get me wrong I think they have done a good job, but when you charge money for things, you have to keep it up to date.
 
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