MGM Low Voltage Cut Off - Owners READ

I have been posting my problem with my MGM 22418 in the thread http://www.rc-monster.com/forum/showthread.php?t=10124

I started this thread because I think it will get more people to comment who
have had a similar issue. My 22418 has the cutoff problem that many have reported. I am using a Flightpower Evo25 6s 5000mah 25c lipo, so my batteries shouldn't be the issue.

I know that all MGM owners don't seem to have this problem, but there seems to be plenty who do. If we can all pool our thoughts together we may be able to get it solved.

I sent the email copied below to MGM tonight


Greetings,

I am having trouble with my new MGM 22418 – 3. It seems that there are many others who are experiencing this similar issue.

My setup:

22418
Neu 1521/1Y
Flightpower EVO25 6S 5000mah 25c
HPI Savage

When I have the controller set to race mode everything works well. I don’t want to use this mode due to the loss of protection to both my Lipo and the overload protection. When I use reduce RPM mode the performance is poor, and I am pretty sure that the controller is reducing RPM even when the battery is full. When I use cut off mode the cut off is initiated anytime I go past roughly half throttle. My Lipo is a very high quality lipo with 125 amp continuous, 175 amp climb outs, 250 amp max burst capability.

I have attached a word document with screen shots from each of these settings. They were taken with the lipo fully charged and the truck being held off the ground. I also set the acceleration to 2.99, the slowest setting. Even when the truck is held off of the ground these symptoms persist.

Please notice the MAX PEAK CURRENT [A] reading for the 3 settings:

Race Mode – 260.55 [A]
Cut Off – 1679.1 [A]
Reduce RPM – 1515.05 [A]

It seems like there is something wrong with the calibration. In Race Mode the max peak current seems reasonable at 260.55 amps. In the other 2 modes the reading is over 1515 amps, which seems unrealistic.

Please let me know what I can do to remedy the situation. I have run auto tune several times and tested all of my connections. Let me know if you need any other information.

Thank you,

Shon Barrett

I have attached the screen shots from my tests. Note that I have the MGM set to the softest acceleration mode and also note the Max Peak Current differences.

It seems that my problem may be much more severe than others are having, but we all may be having the same problem. So far I feel like this is a calibration problem based on the amp draw shown while in reduce RPM mode and cut off mode. If this calibration is set wrong then why couldn't the voltage cut off be set wrong as well? They could be related.

I think that they should make the voltage cut off adjustable, or solve these issues that many of us are having. At $400 this is a considerable investment. If you have similar problems post here and send an email to MGM @ mgm@mgm-compro.cz

If they see that many of us are having this problem maybe they can adjust the software.

Cheers,

Shon

The attachment was missing a screen shot...

If the pictures don't show click on the blank area and the should appear.

Also, I check the voltage of the pack immediately after the tests and my bluepoint meter showed 24.44 volts. It is a very accurate meter. The readings at shutoff show a little over 23 volts. Just something to ponder. I know the cells start to recover immediately.

I realy hope that MGM will take care of use and take this message in consideration. I've a 16018 that i've bought from Mike at RCM who did the same thing too, and yes, for a +/- $400.00 controller it's very frustrating.
I'am sure that MGM can do something for it or Mike at RCM can place little pressure at MGM to solve this problems.

For me, i wait to buy an MMM and my MGM will stay sitting here, maybe to drop on a little 1/10 project latter.

A $400.00 controller, with 160A of capacity, and about just good to drop in a little 1/10 low amps conversion

Hey guys, why not use this and set the controller in race mode??
For $25.00, this unit can almost solve the LVC problem of the MGM controller

http://www.rc-monster.com/proddetail...rod=lisavercar

[bdebde]

I have the 16024, which now runs reasonably well, after 4 motors and 3 batteries trying to sort it out. 20c batteries are the problem, 25c seems to work ok for me (still not for others). I still had to disable the quirky reverse on the thing, because I couldn't stand it. You would certainly think for a nearly $400 controller it would do all things right.

I will certainly upgrade to a MMM when they are out. I too thought about dropping this MGM in a light on road project @ 8s and keep the amps low.

[BrianG]

Originally Posted by bdebde

...20c batteries are the problem, 25c seems to work ok for me (still not for others)...

That would lead me to believe that the LVC on this is too sensitive and is responding to the very brief dips in voltage during high current bursts. MGM ought to add a little delay to the LVC circuit/algorithm.

Does the MGM have an option to increase punch control? That would pull less current from the battery, which would keep the voltage from dipping to the LVC threshold as easily.

No option for the punc control, but we can adjust the time to reach 100% of the full trottle. But somes guys here had try to adjust it but not solve the problem.

I have never tested mine with the cutoff selected, so I set cutoff to on this morn and will see what mine does and I have my accel set to .012 also so it should do it if its going to...I have just reg maxamps 2s and 3s 8000mah in series...I will report back little later today when I get a chance to run it ...

same problem on 16018, at least before it cooked. it blew out the bec first, and still ran with an RX pack or UBEC, and then a couple of fets burnt out. It still runs, sort of.

I had the same cutoff problems, as well as some strange behavior from reverse/brake.

[Just go Play]

Speaking of cooking controllers yesterday I noticed that all the screws that hold the heat sinks in place on my 16018 had started to back out allowing the heat sinks to move around. Luckily I noticed before having them fall off which would not be good for the FET's.

As for the LVC problems I am convinced that if MGM just used a hard cutoff value instead of their variable calculated nonsense we would not be having these problems. The other quirky issues (low speed braking, freewheel not consistant, etc) are bad enough considering the price of these controllers.

On the upside since these problems are all programming issues there is hope that they can be resolved through software updates...preferably before feeling the need to by another controller to replace it.

[bdebde]

Originally Posted by BrianG

That would lead me to believe that the LVC on this is too sensitive and is responding to the very brief dips in voltage during high current bursts. MGM ought to add a little delay to the LVC circuit/algorithm.

Does the MGM have an option to increase punch control? That would pull less current from the battery, which would keep the voltage from dipping to the LVC threshold as easily.

It has accel setting from .13 to 3.0 sec (basically same as punch control on MM). Higher settings help, but then you have no wheely action and lame acceleration.

Originally Posted by bdebde

It has accel setting from .13 to 3.0 sec (basically same as punch control on MM). Higher settings help, but then you have no wheely action and lame acceleration.

Even with my setting set to 2.9 I still have a problem. I think that for some batteries may be the whole issue. You need good lipos to run the types of setups we are running, I accept that. But for most I think the problem has to do with either the LVC being way too sensitive or a factory setting is off. If my batteries were breaking a sweat that would be one thing, but they are not even getting warm. My problem is so bad it does it even when the truck isn't on the ground. Under a light load such as this there is not much strain put on the batteries.

The idea of running an external lipo cutoff or a warning system is a good one, and I am looking into that, but I still think it is ridiculous that we should have to resort to that to get the performance we paid for. Plus we lose the overload protection that truly is a good feature to have.

Those who have had problems try this and let us know what happens. Set the truck to race mode with a full pack and run it for a few minutes. Does your performance increase? Log the data on the computer and compare your Max Amps and your Max RPM.

For me just holding the truck off of the ground and making this comparision I can tell a huge difference. The reduce RPM mode and especially the cutoff mode interfere and cause my performance to be mediocre. As I said on the cutoff setting it won't even go past partial throttle.

[jhautz]

You dont have to loose the over current protection if you just set it to NiMH mode rather than race mode. That disables the internal LVC but not the over current protection. Then you could run the external LVC.

I had sucess with running mine with a slower spool timing, but I do agree it takes some of the fun out of the powerfull setup when you need to dail it down just to keep the oversensative LVC in check.

The external LVC that was linked to below works great by the way. Its no frills and no nonsense. It just works. I use it on a BK 12020 controller and its works perfectly. When the voltage dips below 3.0v/cell it just cuts off. When it comes back above 3.0v it turns back on. So when you hit your limit the truck just kinda starts to stutter a full throttle and you know your pack is about ready to dump but it still lets you drive it back in.

I actually like that solution. Could be a winner.

EDIT: One thing I just remebered... dont plug a half dead pack into that external LVC. It does seem to have a hard time sensing the number of cells in your pack if its not close to full when you plug it in. It might sense a 4s pack instead of your partially charged 5s pack. Could cause a problem if your not carefull.

Originally Posted by jhautz

You dont have to loose the over current protection if you just set it to NiMH mode rather than race mode. That disables the internal LVC but not the over current protection. Then you could run the external LVC.

I had sucess with running mine with a slower spool timing, but I do agree it takes some of the fun out of the powerfull setup when you need to dail it down just to keep the oversensative LVC in check.

The external LVC that was linked to below works great by the way. Its no frills and no nonsense. It just works. I use it on a BK 12020 controller and its works perfectly. When the voltage dips below 3.0v/cell it just cuts off. When it comes back above 3.0v it turns back on. So when you hit your limit the truck just kinda starts to stutter a full throttle and you know your pack is about ready to dump but it still lets you drive it back in.

I actually like that solution. Could be a winner.

EDIT: One thing I just remebered... dont plug a half dead pack into that external LVC. It does seem to have a hard time sensing the number of cells in your pack if its not close to full when you plug it in. It might sense a 4s pack instead of your partially charged 5s pack. Could cause a problem if your not carefull.

NiMH mode doesn't have a cutoff? If so this could be the best solution for now.

[hobbimaster]

I have never tried mt LVC on my 16018 either. I bounce back and forth between 2 4600 7-cell packs and 2 orion 4800 packs, so I just use NiMh mode. In all honesty its easy to know when to stop running a set of lipo's. Performance drops quickly and it will start to slow down. As long as you take notice in performance/speed loss, you'll know its time to pull her in. We use to do this all the time running Novak and LRP speedo's in 1/10th, pre-LVC days.