Mamba Max LVC issues - RC-Monster Forums

eovnu87435ds · **Mamba Max LVC issues -** 12.02.2008, 06:09 PM

Hey I'm having some issues running my mamba max with 5s lipo... I will use a fully charged battery at 21 volts, and run in my mamba, and it will work with no cutoff. but if I try to set a cutoff, it will never arm. I tested at 21 volts, and had the lvc set to 15.7, and it wont arm. I take the lvc off and it runs. anybody know whats going on?

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dirt101 · 12.02.2008, 06:15 PM

way back when I ran my MM on 5s it wouldnt arm on anything over about 20.5V. I always had to slightly discharge my packs, or just not charge them all the way.

suicideneil · 12.02.2008, 06:23 PM

Since the MM is only rated for 3s lipo, Im amazed it hasnt blown up running it on 5s lipo, new or old MM design. I'd say be grateful it works at all and get a seperate 5s lvc; not that there are any comercially available, but a 4s lvc can be tweaked to work with 5s lipos...

BrianG · 12.02.2008, 06:31 PM

Well, it sounds like the firmware isn't set up for 5s to me (from lack of LVC choice). Isn't there an auto setting? Dunno if it even works for 5s though...

But yeah, you're asking a lot from an official 3s (unofficial 4s) ESC. The FETs are probably fine, but I'd be more concerned about those 25v caps - 4v of headroom is not a lot (I like about 25%) - especially if using motor braking (back-EMF pulses can be higher than battery voltage).

eovnu87435ds · 12.02.2008, 07:22 PM

from what i've heard and personal experience the MM works fine with 5s. It does get a little hot so I have it fan cooled. Also, I dont know alot about electrical systems, but Im guessing that if the brakes will back charge the battery, It probably will not charge it as much as was used in the energy to get it moving in the first place. Anyways, I got it down to right at 20.5v and it armed and ran perfectly!

BrianG · 12.02.2008, 08:01 PM

Quote:

Originally Posted by eovnu87435ds

...but Im guessing that if the brakes will back charge the battery, It probably will not charge it as much as was used in the energy to get it moving in the first place.

You can't assume that. An inductor works kinda funny (which is what a motor is really); when you apply the voltage it creates a magnetic field and back EMF/coil resistance limits the amount of current and speed at which it "charges". Once you remove the voltage and depending on how fast the field is allowed to collapse (braking force), the resulting induced spike can be MANY times larger than the supply. However, the battery is a load, which will reduce the spike a lot, but may still be higher than you would think.

Quote:

Originally Posted by eovnu87435ds

...Anyways, I got it down to right at 20.5v and it armed and ran perfectly!

Personally, if you are that close to the edge of working vs not working, some components are being pushed and shortened the lifespan. Who knows, it may work forever.

dirt101 · 12.02.2008, 08:03 PM

I ran mine for months in my revo geared for 43 with a 10xl and it never gave me any problems. I had a fan on it and it never gave me any heat problems either.

Matthew_Armeni · 12.02.2008, 10:58 PM

The only way it is really going to work well is if you A- Don't run the internal LVC, and B- don't run motor brakes. Brian is right, those voltage spikes are big. That being said, I routinely run my MM's on 6s all the time, no problems. I just use mechanical brakes and don't use the LVC.