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3-4 years ago I replaced an Atwood 250 with an Atwood 500. Never had any issues till this year. I've gone thru 13 fuses. Fuse is correct size, 2amp. I have relocated the pump so its easier to access and clean out. I have had the impellor jammed with seaweed and fishing line so I have since surrounded the whole pump with screen so junk isn't jamming it. I replaced the hose thinking it maybe was clogged. I cut out the butt connectors and soldered everything back together. I had a blown fuses a week ago when we got all that rain, I replaced the fuses and the pump ran for 25 minutes to get all the water out so I know it does work. This has me stumped. It is set up to work either manually or on the float switch. Could the float switch be bad?

How long should a bilge pump last? Would the wiring get corroded enough to increase resistance to be the cause of blown fuses? What else might be the problem? Pump overheating?

At this point I'm thinking of a 3 amp fuse and a 2 amp circuit breaker...Or should I just replace the pump?
 

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You might also look for poor connections in the wiring, or even corrosion in the wire itself - these will also raise the current draw on that circuit.

Another thing to look at - is the impeller in the pump free of any obstructions? (weeds, grass, fishing line, etc) A sticky or partially impeded impeller will take a lot more amperage to turn = blown fuses.....
 

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Discussion Starter · #5 ·
QUOTE(garry454 @ Jun 23 2009, 10:43 AM) <{POST_SNAPBACK}>You might also look for poor connections in the wiring, or even corrosion in the wire itself - these will also raise the current draw on that circuit.

Another thing to look at - is the impeller in the pump free of any obstructions? (weeds, grass, fishing line, etc) A sticky or partially impeded impeller will take a lot more amperage to turn = blown fuses.....

I have considered rewiring but don't want to unless all other options are eliminated. The impellor had been getting stuck by weeds and line, but the screen was suggested by an earlier post and has been added. However, there was a small piece of weed the got sucked in through the screen the last time it blew. If a tiny piece of weed is going to stop the impellor and blow the fuse, then there must be others with this same issue and a way to fix it. If I need a 1500GPH pump I'll do it, but it better suck out everything that gets in there.
 

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Try raising the fuse to a 2.5 amp fuse.. You don't have to worry about the wire burning up because it should be at least 16awg wire and 16awg wire is rated for I'm pretty sure 15amps. If it still blows I would check the resistance of the wire which should be right around 5.3 ohms per thousand feet of wire if it's 16awg and 3.25 ohms per thousand feet if its 14awg wire. . If the resistance is equal to or less then the above numbers then the wire is good, If it's above those numbers (depending on the wire size of course) then you have either corrosion or a loose connection. Corrosion or loose connections = Resistance and Resistance = higher amperage draw and you will need to find the corrosion and get rid of it or find the loose connection and fix it. If the Resistance is fine then you need to check for a short in the wiring. If there is no short then the wiring is fine and the only thing left is the pump or float switch. If it gets to that just replace them and be done with it.
 

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Discussion Starter · #7 ·
mechanic at the marina said to just replace the pump after everything I told him I've done. Its getting to warm and blowing the fuse. Thanks for all the advice.
 

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I just bought a new bildge pump and the instructions say it draws 2.5 amps but to use a 5 amp fuse. Thinking of your problem, I looked at the pumps that draw 2 amps and they said to use a 5 amp fuse on them too. I guess they need more power to start then run at the rated amps.
 

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Well, I was thinking that a 2 amp fuse was a little small, but I just happened to still have the package from a 500GPH pump that I put in a while ago, and it calls for a 2.5 amp fuse granted a little bigger, but it also has a built in water sensor circuit.

Funny thing though... it's rated amp draw is at 2.5A at 13.6 volts, so you'd think it would be cutting it TOO close to use a 2.5 amp fuse.

Interesting also is that it only rates it at 1.9 amp at 12v (the performance also drops about 20% when running at 12v)

Did you replace or change your charger in the past year? Is it possible that you are now running a higher voltage to the pump when it's sitting (constantly on charge vs not being charged) and that might explain why you are drawing more current than in past years??

I would think that over time a pump might increase current draw as junk accumulates around the shaft seals, but I have run pumps YEARS AND YEARS and they still are good. In fact two of the pumps on my boat are original equipment from 1983 and they still perform just fine.
 

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QUOTE(KMC @ Jul 7 2009, 08:17 PM) <{POST_SNAPBACK}>Well, I was thinking that a 2 amp fuse was a little small, but I just happened to still have the package from a 500GPH pump that I put in a while ago, and it calls for a 2.5 amp fuse granted a little bigger, but it also has a built in water sensor circuit.

Funny thing though... it's rated amp draw is at 2.5A at 13.6 volts, so you'd think it would be cutting it TOO close to use a 2.5 amp fuse.

Interesting also is that it only rates it at 1.9 amp at 12v (the performance also drops about 20% when running at 12v)

Did you replace or change your charger in the past year? Is it possible that you are now running a higher voltage to the pump when it's sitting (constantly on charge vs not being charged) and that might explain why you are drawing more current than in past years??

I would think that over time a pump might increase current draw as junk accumulates around the shaft seals, but I have run pumps YEARS AND YEARS and they still are good. In fact two of the pumps on my boat are original equipment from 1983 and they still perform just fine.
Amperage draw and supply voltage are too different things.. High voltage alone will not blow a fuse. A high voltage spike would more then likely fry motors and or circuitry involved and once fryed you would more then likely have a dead short causing the fuse to blow.

Supply voltage has little to do with amp draw on a motor unless the supply voltage is low.. If the supply voltage is a little low the motor will work harder and draw more amps and this may cause a fuse to blow if the motor is unable to reach it's rated speed. A motor is rated on full load amps and running amps.. When it first starts it draws full load amps until it reaches speed then it drops to running amps and the amps will raise and fall depending on the load to the motor.. The fuses are rated above full load amps so that they will not blow at startup. If for any reason the motor starts working harder then what it's rated for, the motor will draw more amps then what it designed for and blow the fuse.
 

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While most of that it true for induction or AC motors, DC is directly dependent on incoming voltage to determine what the consumed current would be (and yes, the current is also related to the load on the pump). More voltage, more RPMs and more current (and probably more pumping). This would only work to a point though, and you're right it would eventually fry the motor. However, within the normal range of encountered voltages (~11-14VDC) I would not expect damage and I would not expect to have to replace fuses.

My point was that a similar pump to his (500GPH Rule instead of Attwood), is rated at a current of 2.5A during running conditions, but is recommended to use a 2.5A fuse... seems pretty close to me. If I ran this pump exclusively when the batteries were in a non-charging or partially-discharged state, It will only draw 1.9A and I would be provided with at least a 20% headroom to the capacity of the recommended fuse. I would think if a locked rotor condition were to occur (like debris got stuck), then the current would increase and blow the fuse as it should. HOWEVER, if I were to run this same pump exclusively when the batteries were charging, I would be constantly running right at the recommended fuse capacity

I'm not sure exactly which model Attwood we're talking about, but checking their site they have a 500GPH model which draws 1.5A at 13.6VDC, 1.3A at 12VDC ( lower current draws than my 500GPH Rule) but is still recommended to use a 2.5A fuse (same as mine)
 

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Discussion Starter · #12 ·
Nothing has been changed on the boat. Batteries never sit more than a couple days without me running the boat. I had had the marina order a new pump but they don't make that style anymore. So far it seems that the fabric screen around it has worked. I have not had a fuse pop since. Odd that the pump motor might have been getting warm before but now its not.
 
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