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Old 23-08-2009, 05:38   #1
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Switching a High Amp Bilge Pump

Have a rule 3700 pump that needs a 25amp fuse.
Want to use Contura Waterproof Bilge Pump Control Panel - Blue Sea Systems
to switch it, but it only goes up to 20 amps.
So the question is, how do you switch high amp pumps in your boat?
I guess I could bypass the fuse and put in a 25 amp fuse instead, but not sure if that would be safe.
Thoughts ?
Bob
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Old 23-08-2009, 05:49   #2
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Quote:
Originally Posted by bobfnbw View Post
Have a rule 3700 pump that needs a 25amp fuse.
Want to use Contura Waterproof Bilge Pump Control Panel - Blue Sea Systems
to switch it, but it only goes up to 20 amps.
So the question is, how do you switch high amp pumps in your boat?
I guess I could bypass the fuse and put in a 25 amp fuse instead, but not sure if that would be safe.
Thoughts ?
Bob
Run it through a relay.
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Old 23-08-2009, 05:57   #3
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Use the Contura switch to provide switching input to a relay. A standard 30 amp automotive relay will work fine if the location for it is dry. The fuse in the Blue Sea panel will now be protecting the conductor providing the switching input to the relay and should probably remain the 15 amp fuse that was shipped in the panel

To protect the pump's B+ (brown) wire, install the 20 amp fuse required by Rule in the B+ supply to the relay taking into account: the fuse should be close to the conductor's connection to the bus bar and should be accessible for easy replacement.

Hope this helps,
Charlie
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Old 23-08-2009, 14:50   #4
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Relay + separate fuse.

b.
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Old 23-08-2009, 21:17   #5
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If you put the relay directly behind the switch, you can rewire the fuse to the pump-circuit, so that the front-accessible fuse is the one likely to blow. If you put AWG-14 or so between switch and relay, you could even skip the fuse there. The coil in the relay is very thin wire, acting as the fuse.

But before you do this, check the amperage again. I don't think the pump draws more than 20A (I am sure of it actually, not even the Rule4000 draws 20A and my Rule 8000 is two 4000's coupled on an output-manifold and each 4000 is switched with a standard 20A switch). They just specify a 25A fuse because that is what the wiring can take without problems and they want to oversize the fuse a bit for an important system like this.

There's another switch to keep in mind: the float switch.

cheers,
Nick.
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Old 24-08-2009, 02:24   #6
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I am unfiamiliar with the relays you all mentioned.
I did a search, found this.... is this what you mean ?
If not got a link please ?
Thanks.
Bob
Digi-Key - PB681-ND (Tyco Electronics <!--Potter & Brumfield--> - 1432786-1)
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Old 24-08-2009, 05:51   #7
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The Tyco solenoid you found is correct.

The Rule 3700 (Model 14A) draws 15.5 amps with a 25 amp fuse/circuit breaker specified: Rule 3700 > Bilge Pumps > Pumps > Rule - ITT

The rating of the over current protection device is required to be specified by the manufacturer of pumps and other rotating equipment to mitigate overheating problems caused by a locked rotor.

My advice; do the job correctly.

Best regards,
Charlie
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Old 02-09-2009, 18:48   #8
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Keep in mind if it is fused at 25A, any inductive motor type device (electric motors of any kind including pumps) have a MUCH larger inrush current for a few milliseconds until they are up to speed.

If it is fused at 25A, it almost certainly draws much less than this. Not to say you should be using it with a switch that can only handle 20A but this is something to keep in mind in reference to wiring etc.

Just dont want to see you end up with welding cable run into your bilge
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Old 02-09-2009, 18:54   #9
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I second Charlie's advice: do it right, i.e., use a CPD of the size recommended by the pump maker.

The real danger here is of the pump itself burning up in the event of a locked rotor and a CPD larger than that recommended. Even a slightly higher fuse/breaker could carry all the current needed for the rotor coil to heat up and start burning.

Bill
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Old 02-09-2009, 19:19   #10
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First, you have to gauge the wire for at least 25 amps. The switch (or solenoid) has to be rated for at least 25 amps and of course the fuse must be no more than 25 amps. Anything different and it is not wired safely.
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Old 02-09-2009, 22:39   #11
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AFAIK, the manufacturer only states the fuse to be rated at 25A and is silent about the switch rating??

The fuse protects the wiring (so wiring must stand 25A, which is a silly thin AWG16) and the switch must withstand current at the fuse rating. Read on, here it comes: A 20A switch is rated at that value because you can use it to break a circuit carrying 20A many times before the contacts burn up. But when the switch is just on, it can handle much more. As long as the pump draws 20A or less when running (no locked rotor amps or start-up amps are relevant) you can use a 20A switch for it. Short overloads like during start-up are provided for in switch ratings. Get the full specs if you don't believe me (it's called intermittent and continuous ratings for 3 states: switching on, being on and switching off. The latter one is the lowest rating because switching off causes more arcing)
I would never ever use a relay or solenoid on a bilge pump. The failure rate of these are just too high for this crucial device. If you really want to over-engineer it, use a bigger switch, no matter what needs to be done for that.

ciao!
Nick.
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