Trouble with MGM 22418 - HELP!!!

I am having the LVC problem that others have written about. In this case I really don't believe my batteries are a problem. Here is the setup:

MGM22418
NEU 1521/1Y
FlightPower 6S 25C 5000mah

I had previously setup the controller using the "Reduce RPM" Low voltage cutoff setting. I decided that I would rather have the protection of the "cut off" mode. I also noticed when I was checking the data after a run that the value "Current in full throttle [A]" never had a value. I assume that that value is never present because the controller never actually goes to full throttle. The truck seems to run good when in the reduce RPM mode but cuts off in "cut off" mode. I have previously run autotune. I thought maybe I had a bad solder joint on my Deans so I re-soldered them all.

Does anyone have any idea what is going on. My battery is pretty good, everyone seems to have good luck with this FlightPower. Connections are good. I have played with lower acceleration settings with no luck. Ideas?

[bdebde]

For the "amps at full throttle" to read anything, you need to hold full throttle for several seconds. It took me quite a while to actually hold full throttle long enough to get a reading there.

I had problems with 2 different brands of 20c batteries, but switched to Neu 25c batteries and no problems. I would think the 25c flightpowers would be up to the task.

What acceleration setting are you running?

Originally Posted by bdebde

For the "amps at full throttle" to read anything, you need to hold full throttle for several seconds. It took me quite a while to actually hold full throttle long enough to get a reading there.

I had problems with 2 different brands of 20c batteries, but switched to Neu 25c batteries and no problems. I would think the 25c flightpowers would be up to the task.

What acceleration setting are you running?

I've pretty much tried them all. I have it at .36 now. These batteries should be able to handle this.....

Any other thoughts?

[bdebde]

Does it work ok in the "reduce rpm" mode? Is the battery new, do you have another good one to try?

On reduce RPM it works. The battery is new, only 4 or 5 cycles on it. I think I may not be getting the full performance in reduce RPMs. I hold full throttle for long periods of time (across big fields) and I never have "Current at full throttle" data.

I don't have another battery to try unfortunately. I was going to get another one of these FlightPowers because I have been pleased with the runtimes but now I don't want to spend the cash. Could it be the MGM?

I misspoke, I meant to say I have the acceleration set at .39s

I just verified that something is wrong. I set the controller to "race mode", held the off the ground and pulled full throttle. Max RPMs measured 39500. I switched to "reduce RPMS" and max throttle doing the same test was 36200. So obviously the controller is limiting power due to the LVC. The question is are the batteries the problem or is it the MGM? I don't have another battery so I am kinda screwed. I don't think its the batteries though. They don't even get warm, not even a little when I run this truck. They don't seem to be strained. Voltage on all cells is 4.16 after this little test. They are supposed to be quite up to the task, so.........

Suggestions?

[bdebde]

It may just be the MGM, others have still had trouble with good batteries too on high powered setups (that 1521 is going to pull alot of juice). If it works OK in "reduce rpm" mode I would just run it there, it will still cut off if the voltage gets too low, and you will know it before then because it will really start lacking power (reduced rpms) before it gets to that point. I run the same accel setting and" reduce rpm" mode with no problems on 6s with 1515 2.5D.

What kind of max amps reading are you getting?

It works on reduce RPM but I am not getting the performance I paid for. I would have been better off with a less powerfull setup. When I use the reduce RPM mode it limits the RPM even with fresh batteries as my test showed by switching to race mode and checking the max RPM. It is noticibly more powerful even when just holding the truck off of the ground when in this mode.

I don't know how many amps I am pulling. It always shows some number above 2400 in the maximum amps field. I never have had a figure in the amps at full throttle.

Also the cutoff is not user adjustable as is stated on the rc-monster store. Nowhere in my instructions or on the PC program is there any way to adjust the Lipo or NiXX voltage cutoff

[bdebde]

Yeah the cut off voltage is not adjustable, factory set at 3.1 according to MGM. If you are seeing max amps of 2400, then I would say you need larger batteries to maintain voltage. It may also be possible that you are seeing the current limiting feature in the MGM (which is disabled in race mode). Even running a Big Maximum on 6s, I only saw max of 900 amps and with the current 2.5D it only runs 400 - 500 amps. Even thought these values are not accurate (according to MGM) they do give some indication of the maximum amps of your set up. I would try a larger capacity battery if at all possible, to see if you are in fact dropping the voltage too low. Perhaps try 2 of your current battery in parallel.

Originally Posted by bdebde

Yeah the cut off voltage is not adjustable, factory set at 3.1 according to MGM. If you are seeing max amps of 2400, then I would say you need larger batteries to maintain voltage. It may also be possible that you are seeing the current limiting feature in the MGM (which is disabled in race mode). Even running a Big Maximum on 6s, I only saw max of 900 amps and with the current 2.5D it only runs 400 - 500 amps. Even thought these values are not accurate (according to MGM) they do give some indication of the maximum amps of your set up. I would try a larger capacity battery if at all possible, to see if you are in fact dropping the voltage too low. Perhaps try 2 of your current battery in parallel.

I get the feeling that the MGM is just calibrated wrong. The 2400 amp value is just not realistic even for an instant spike.

I am looking at the eagle tree right now, the only problem is if it confirms my problem I'll really be no better off.

[MetalMan]

Is purchasing the eLogger V3 (formerly MicroPower) an option for you? This would tell you what is truly going on with your setup.

[bdebde]

It is too bad the MGM doesn't give an accurate amp value, it would really be helpful. I have found with my set ups (just a guess), that the actual value may be around 1/3 of the reading you get there.

Can you gear down any and see what happens?

I know I was at my wits end with the MGM for a while, after trying 3 motors and 2 different 20c batteries, and still no difference. I was to the point where I thought that something was wrong with the controller. Finally got a Neu 25c battery and it works OK now. It is drivable now after all the messing around and finally disabling reverse, but I will likely replace it with a MMM when they come out, just because the MGM is a bit quirky.

[jhautz]

I ran an eagle tree on my MGM at one time trying to diagnose the exact same issue. At the time I had 3 MGMs. All 3 did the same thing. They would start cutting out after only 5 minutes or so of runn on my 20C packs and in some cases started doing it right away if I set the motor spool up time to a low value to really give it punch. What I found was the eagle tree was telling me that the owest voltage it recorded was 3.4v/cell and around 110Amps. Then I took the exact same buggy and swapped out the MGM for a Quark 125 and it the cutting out went away and it ran perfectly. With the Quark I was able to hit spikes as hig as 130amps and the voltage dropped down to 4.25v/cell. When the quark started triggering the LVC I took the 5000mah pack and charged it all the way and put back aroun 4750mah. With the MGM if I stopped as soon as the LVC kicked in I could only get 1100mah or so back in.

In all honesty on the track I didnt really even notice the issue cuz I set the spool up time to a higher value and it pretty much masked the problem. I noticed it more when I was bashing and wanted to do high speed runs and drag races on pavement.

Anyway... I guess I kinda started to ramble here.... To summarize: I found the LVC on the MGMs to be more like a 3.4v/cell cut off rather than tthe 3.1v they report. The amp reading on the MGM software was about 4 times what I measured with the eagle tree.
A reading on my MGM of around 490A measured only around 120A on the eagle tree.

[BrianG]

Wow, those amp values sound wayyy off! AFAIK, the only two ways to measure current is measuring the voltage drop on a series-connected shunt, or use a inductive clamp. The clamp could be a coil of wire wrapped around one of the phases, but I doubt it. The shunt could introduce too much voltage loss (especially on a 224A ESC), so I don't see them doing that either.

The only other way I could see it working is if the software watches the battery voltage drop to calculate a very rough current value. But that requires some assumptions made about the output resistance of batteries and that they are all the same, which they are not.