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Ballast Tank Motor Relay & NiMh Question - Hunting for a 12v RC relay

R/C Submarine modelers

Postby safrole » Wed Aug 06, 2003 10:34 am

I just got my Robbe U-47 and a 750ml Engel piston tank. I know I could use an ESC to operate the tank, but I would prefer to use a relay, since there will be upgrades in the future that would be better suited by momentary full voltage. In any event I am trying to avoid rigging up a servo with a cam/microswitch setup which I foresee being less accurate when I'm "bumping" the tank to try to hover. Please tell me what I'm missing. I have a Futaba Skysport 6 (surface frequency).

Another junior question...
I bought two 3Ah NiMh battery packs. Does the physical size of the battery (C, sub-C) affect my battery endurance? I thought the amp hour rating was a rating of total capacity. So do smaller sized 3Ah batteries last about as long as larger 3Ah batteries?

Thanks for your time,

--Jason Overhulser
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Postby raalst » Wed Aug 06, 2003 12:03 pm

You are correct in that the Ah value (or mAh) is a measure
of total capacity. it tells you the battery can deliver
1 amp of current during X hours (3 in your case)
or e.g. 2 amps during 1.5 hours. The more amps are
consumed by the electronics, the shorter the battery
lasts. sounds logical..

The types and sizes of battery differ mainly in how fast they
discharge when short circuited (do *NOT* do this).
The rate of discharge is in Amperes (Amps) and
high quality batteries can produce more amps than
lower quality batteries (at any given time). So, high
quality batteries are capable of discharging faster.

This behavious is called internal resistance because
it seems there is a resistor inside the battery limiting the
amount of amps it can produce at any time.
High resistance = low quality

A perfect battery would in theory discharge in 0 seconds
with gazillions of amps (and a large BANG undoubtedly)
because there is no resistance in a (perfect) short circuit.
Volts = Amps x Resistance, with Resistance = 0, the amps
can go sky high.


Ronald van Aalst

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Postby Robse » Wed Aug 06, 2003 2:08 pm

Hi Jason..

About the relay Q: I have used two relays from Graupner, "Mini Switch 40", stock no. "3294".

In short, it's a >15A relay for 12VDC use, remote controlled. It's normally used to reverse engines, or as a (EMC??) brake, but it can easily be used as a remote controlled switch. It's about 1x1x1/3 inch, with a curcuid board and SMD components mounted on one end. (Small, but powerfull...)

Take a look at Graupner's homepage( ), and search for either type no, or stock no.
For initial data, take a look at my page:

(Sorry for my spelling, but I'm about as tired as a complete retirement home..)
Yours Sincerely, Robert Holsting, Denmark
1/81 SSBN Ohio Class scratch builder, more at

"Never be afraid to try something new; remember that it was amateurs who build Noah's Ark, and professionals who build the Titanic"
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