Problem with my Homemade Boat!

[Emerson H-W]

I have a homemade boat that I have to launch on Saturday, but I need some help ASAP with a problem. Pretty much, when I push on the throttle, the motors run and then die off within a few seconds.

I have two Graupner speed 700 Race (9.6v) motors with a Victory series ESC and I interchange two 9.6v batteries, one is 3500 mAH and the other is 4200 mAH, both are NiMH.

At first, I thought is was the speed control and I talked to Montana Designs (the company that makes it) and they said it may be because it is set up for LiPo use and not NiMH, but then I plugged the motors directly into the battery pack, and I still had the same problem. I re-soldered the wire connections to the motors and I am using new Deans plugs on everything.

Could this problem be because of a bad connection somewhere in the system?
Again, I am leaving on Saturday and I am really trying to get this boat that I made working in the water by then.

[Shaun Hendricks]

Sounds like the batteries can't hold up the amp draw from the motors. Are the batteries hot after the motors die down? How do they charge after that?

Again, the batteries sound tired. Try a fresh pack (that has gone through a proper break-in process) and see what happens. If it still does it, it sounds like the power is being sucked off someplace.

Try one motor at a time. If one runs great and the other badly, then you have a mismanufactured motor. There is likely a short in a winding or something of that nature. Get a new one if that is the case.

If it isn't either of them, then the combined drain of the motors is probably to blame, too much drain on the batteries. You'll have to rewire for either a parallel battery set, use higher drain capacity batteries, or wire the motors in series to halve the drain they put on the system.

Those are the only solutions I can think of at the moment. :confused:

[Umi_Ryuzuki]

The Graupner speed 700 Race draws 3.3amp no load.
http://homepage.ntlworld.com/edward.matthews/ddmbc_files/motors/graupner.htm

Now for some reason my brain is failing to do math today...
But I am thinking that would run about 10 minutes on your batteries.

If the motor is drawing 6amps due to your set up then your run time will be half.

:confused:

[Aerominded]

If we are talking a matter of seconds, I have to ask... Have the batteries been charged? :confused:

[Ghost 2501]

If we are talking a matter of seconds, I have to ask... Have the batteries been charged? :confused:

ya know Aero. I think that there may well be some possibility that they are indeed a tad on the flat side.

I have also noticed on both my ni-cd and ni-mh packs, that if left fully charged for a few weeks, the charge will infact discharge over time. yes even ni-mh and ni-cd packs have "half lives" regarding charge levels

[420TEE]

How old are these batteries? May be time for new. Sounds like this is not your first boat. Do these batteries work OK in another application? Plugged straight in all you've got are batteries and motors. Must be one or the other.

[mfr02]

It does sound like uncharged batteries. I have on occasion been caught out by a charger not actually charging.

[LtDoc]

Basing things on two motors and a 4200 mAh (4.2 Ah) battery, and assuming no other loads at all and a fully charged battery, you should expect something close to about 30 minutes of run time (NOT an exact/realistic number figure, but close). Since you aren't getting anything close to that amount of run time, the first thing that comes to mind is that the battery(s) doesn't have a full charge for some reason. The next thing that comes to mind is that the draw current of the motors is more than stated. If they are drawing something like 25 amps instead of 3.3 amps each, you'll end up with a short run time like you're seeing. A 'loaded' condition instead of a 'no loaded' condition. That also brings in the capability of the ESC, can it handle 25 amps? I have no idea...
Good luck!
- 'Doc

[Ghost 2501]

It does sound like uncharged batteries. I have on occasion been caught out by a charger not actually charging.

I have also done that, however I plugged the charger to the wall, plugged the battery to the charger and left it at that, what I didnt do is turn the wall socket on! :o D'OH!!!!