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Re: [TowerTalk] U.S. Tower MDP-750 motor failure and related prolems

Subject: Re: [TowerTalk] U.S. Tower MDP-750 motor failure and related prolems
From: Les Kalmus <>
Date: Mon, 20 Dec 2010 09:06:25 -0500
List-post: <">>
  The low voltage comments below are very accurate.
I believe the max voltage reduction should be limited to 3% to maintain 
proper operation.
You should plan your wiring accordingly.
Also, if you double up on wiring, the result you get, if you use two of 
the same size wires is is the size -3.
I.e., 2 x #14 in parallel = #11.

Les W2LK

On 12/19/2010 11:36 PM, Richard (Rick) Karlquist wrote:
> On 12/19/2010 7:31 PM, Victor Morris wrote:
>> Aloha everybody,
>> I'm new to this group and I'm looking for some help. Earlier this year I 
>> purchased a TMM-433 HD tower from U.S. Tower. I chose the option with an MDP 
>> 750 motor, inside control box, and outdoor relay box.
>> Almost from the beginning I've had trouble. It started with what appeared to 
>> be an intermittent problem with a stuck outdoor relay. Sometimes the tower 
>> would not raise when e I turned on the power. However if I went outside and 
>> tapped the box, the tower went up fine. I thought this was just a nuisance, 
>> but I may have been wrong.
>> About 3 weeks ago a circuit breaker tripped one time when I tried to lower 
>> the tower. I reset the breaker and the tower lowered properly.
>> Vic, AH6WX
> The biggest user caused problem with these things is insufficient
> wiring.  If the wiring is marginal, the breaker may or may not
> trip depending on temperature and other conditions.  The motor
> draws 20A @ 120V.  That is a 6 ohm load.  The round trip resistance
> of wiring back to your *service entrance* should be only 5% to at
> most 10% of this.  For 10%, this works out to 200 ft of 12 AWG wire.
> And that's marginal.  I use doubled up 10 AWG wiring for mine, and
> it just barely starts on hot days.  I believe it is well known
> that insufficient voltage on motors is bad for them.  Of course
> leaving the power applied to a motor with a dead starting cap
> can't be good either.  Starting caps go out all the time.  I
> used to have a pool pump motor that went through caps at the rate
> of a new one every year.
> I have traced out the circuit for my MDPL1000 and can send it to
> you if it is helpful.  You will probably have to use it as a guide
> and trace out your own version.  There are two relays in cascade.
> The timed ones seem to be the most troublesome.  I had to replace
> both of mine.  However, I cannot think of any way the relays could
> damage the motor.
> I always stand outside by my tower and watch it go up and down.
> I just don't trust these things.
> Rick N6RK
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