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Author Topic: A question of Amps?  (Read 1128 times)

pugwash

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A question of Amps?
« on: August 03, 2010, 05:35:34 AM »

This is two questions in one post aimed at the more technical electrically minded members.
First I have two small switches which I would like to use in the wiring loom.  They are from the
same maker - one has on it 1.5amps at 250v the other has 3amps at 125 v but what amps will the
switch cope with in a 6v system and is there a formula to work this out in future.
Secondly the boat is fitted with 2 MFA  Torpedo500 motors marked 4.5v - 15v is there any way of
calculating  approximately what they will draw from the battery at 6v.
If there is an answer I am sure someone out there can supply it

thanks  Geoff
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DickyD

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Re: A question of Amps?
« Reply #1 on: August 03, 2010, 08:26:25 AM »

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Watchleader

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Re: A question of Amps?
« Reply #2 on: August 03, 2010, 07:28:20 PM »

It aint quite as simple as it may seem.

Switch are rated  in terms of volts by the insulation quality, and creepage and clearance distances inside the switch.
ie. the ability not to short out (flashover) when said voltage is applied.
The "amps" is the rated current carrying capabilty of the switch contacts.
This is also dependent on whether the switch is to be operated with the load applied, or operated  before the load is applied.
The contacts will break down (burn) faster if they make contact with load applied.
2
The amount of current required from the battery will depend on how much work the motors are doing.
Free running with no prop in the water, or small prop and small hull - realatively little current will be drawn.
Large prop pushing a lage hull, will require a lot more current.
The more the motor is loaded the more current required.
Increasing the applied voltage for the same power requirement will reduce the current.
Hope this helps.  O0
John
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bosun

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Re: A question of Amps?
« Reply #3 on: August 03, 2010, 09:27:17 PM »

Took The Words Out of My Mouth John, %% :-))
Ring you later.
Bosun
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pugwash

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Re: A question of Amps?
« Reply #4 on: August 03, 2010, 11:17:57 PM »

Thanks to you all - I think I have enough info to work things out, I did find out about the motors, just got
a bit confused as they no longer make this mark but it appears to be the same as the MFA540/1 - its exactly
the same in dimensions etc so I've used the data from this motor.  As for the switches between John and
SWMBO (with her A-level physics) I think I should be OK.  I suppose rule of thumb if the switch starts to smoke
its not man enouth for the job.   I have no trouble with mains electricity, I have done three full rewires on my
previous homes and they are still standing, but I always had problems on the yacht with 12v and it seems to
have carried on to 6v.  No more dumb questions - I hope

Geoff
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