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[Boathound]

Hi, just a quick question- my boat runs just fine then when it has used about half of the juice in the batteries I loose control of it.  
It has three motors, 2 nicad packs, power distribution board a mixer/speed controller and another speed controller. The receiver is very close to the mixer and motors. Any ideas?

Took me over 5 hours to recover it on wednesday..... it was a big lake!

[Dueller]

I'm no expert so may be corrected. It may be the voltage drop in the supply to the speed controller, many of them cut out at 6v as a safety feature. If you start with 6v then you are close to the limit already. Rechargeables also lose their voltage in a different way to alkaline. Alkalines have a steady voltage drop as they are used, rechargeables (almost) keep their rated voltage and then tend to drop off suddenly at the end.

When you lose power, i would suggest a voltage check on the pack to see what it is producing. Dont forget that by the time you recover the boat the batteries may have recovered a bit so try and run it again untill it cuts out.

[stallspeed]

Boathound,a bit more about the make and model of the equipment is a help.
Could have a radio failsafe that has not been set, but who is to know?

[Shipmate60]

It is  a Futabs Skysport 6 witth a ACTion Condor and ACTion P94 in a Graupner ARTR Scharnhorst.
Not sure on the batteries, that answer will be along soon I hope.

Bob

[Boathound]

Batteries are 8.4volt 4600mAh

[barriew]

Separate Rx battery or using FLJ's favourite device - a BEC?

Barrie

[Boathound]

Whats a BEC?

[Shipmate60]

Battery Elimination Circuit.
It allows the main power batteries to power the receiver.

Bob

[Boathound]

Its a Bec setup then

[FullLeatherJacket]

NiMH or NiCAD packs? If NiCAD, could be "memory".
Drop-out voltage on P92 BEC is 5.5v.
My main concern is that you are using two parallel packs.
FLJ

[Boathound]

How would I connect in an independant battery pack for the receiver, would I connect it to the distribution board or via the mixer?

[Shipmate60]

Direct to the receiver via a switch harness.

Bob

[FullLeatherJacket]

How would I connect in an independant battery pack for the receiver, would I connect it to the distribution board or via the mixer?

Neither. There should be a set of pins in the receiver, usually in the end slot where the servos plug, marked "Batt" or similar. That's where your separate battery harness goes. Don't use the 5v flylead from the P92 at the same time (although that would go into the same slot in the Rx).
Having mulled this one over I reckon that you have a battery problem here. Either you aren't charging them up for long enough, or they don't have the capacity you would have them hold, or there's a duff cell in one pack which is bringing down the other cells.
Discharge the packs down to 1v per cell, using a 12v car bulb and measuring the voltage across the bulb with a digital meter. STOP AS SOON AS THE READING GETS TO 7V. Recharge them at a known current and for a measured time, allowing about 140% of the maH capacity i.e. charge at 460mA for 14 hours (or pro-rata for different charge current).
You should now run the boat using one pack at a time and see if one is markedly down on the other one as regards the time to get the model down to horribly slow. Your idea of using a separate battery for this test is a good one, but if the battery is good then it should hold at least the 5.5v required to keep the BEC going.
FLJ

[malcolmfrary]

NiMH or NiCAD packs? If NiCAD, could be "memory".

The way "memory" in NiCads works is that there is one" less good" cell than the rest in the pack.  It doesn't charge as well as the rest, leaks electric a bit faster, and ends up discharged sooner.  At this point, it tries to reverse charge, initially dropping the 8.6 volts down to 7.2, but rapidly trying for 6.0, but with very limited current, so if a high current is demanded, the voltage will drop yet further.  When it gets recharged, the bad cell has even further to charge up to a point where it is usable, and the sequence repeats, only worse. 
I heard a rumour that NiCads will soon be unobtainable, so when an increasing number of manufacturers make MiMHs with a steadily reducing standard of expertise, I suspect that NiMHs will gain reports of "memory".

[Colin Bishop]

I think NiCads have been effectively banned for most applications in the EU for some years now. There are a few specialist exceptions I believe.

[Inkmark]

Colin
Slightly off the thread but I have just splashed out on a Futaba 2.4 gig set and it has NiCads.
The voltages on both Transmiter and receiver go down really fast, so I will probably change these for NiMh.
Cheers
Mark

[FullLeatherJacket]

The other possibility is that your motors are drawing more total current than you think. You do have three of them in this model, and that's no small load on the batteries unless you have very low-current motors and are niggardly with your use of full throttle.
FLJ

[Colin Bishop]

Slightly off the thread but I have just splashed out on a Futaba 2.4 gig set and it has NiCads.
The voltages on both Transmiter and receiver go down really fast, so I will probably change these for NiMh.

Yes, I had them on my 6EXE 40mhz I bought a few years back and they were only 700ma which is a bit mean to say the least. I have changed mine for 2100ma NiMH.

I don't know how the EU regs impact on imported stuff - maybe somebody will know.

Colin

[Boathound]

I would like to thank everyone for their interest and very helpful responses.