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WakeWorld Discussion Board » >> Boats, Accessories & Tow Vehicles Archive » Archive through January 14, 2005 » Issue with drop in voltage when running pump « Previous Next »
By Nate (norcalmalibu) on Monday, September 27, 2004 - 10:17 pm:    Edit Post Delete Post
In my 89 skier, I have a reverse pump for my ballast system. This problem gets worse everytime I go out. When I hit the switch to pump it out nothing happens and the voltage almost goes to 0. One time i left it with it on as the voltage was pegged and a wire almost caught on fire started smoking. I have sense added another battery and the problem is still there. To get it to work I usualy shut the boat off turn it back on and flip the switch up and down from fill to drain back and forth and sometimes it turns on. Im not that good with electrical so any ideas on how to get this pump to turn on everytime without melting wires would be great thanks

By Doug Gierosky (d_fresh) on Tuesday, September 28, 2004 - 4:20 am:    Edit Post Delete Post
Not knowing your set up, it's difficult to diagnose the problem. Are you controlling the motor current through switches, or relays? What gauge wire are you using? Do you have any pics?
By teddy (amixman) on Tuesday, September 28, 2004 - 6:22 am:    Edit Post Delete Post
nate u either have a failing pump or a short in the wite i would think the former because a short doesent go away after u flip the switch, either way u have serious elect hazard that u need to fix before u use it again!!!!

unplug the pump turn the switch on if your gauge doesent do anything change your pump and the melted wire, if it pers on 0 start hunting 4 a short

By Rod McInnis (rodmcinnis) on Tuesday, September 28, 2004 - 10:25 am:    Edit Post Delete Post

You have at least two problems that you should correct before you burn your boat up!

The entire purpose of a fuse/circuit breaker is to protect the wiring. If you had a wire start to smoke it is a clear indication that wire is too small or the circuit breaker / fuse is to big (or perhaps you don't have one at all).

The second problem is that your pump is drawing excessive current. if it starts sometimes and not others then I would suspect that the motor on the pump is damaged and needs to be repalced.

If the wire started to smoke then it is definately damaged and should be replaced. I suggest overhauling the entire pump, wiring, switch and circuit breaker to make sure everything is sized properly and doing its job.

By Nate (norcalmalibu) on Tuesday, September 28, 2004 - 11:09 am:    Edit Post Delete Post
Thanks for the input, the wire that it is connected to has a inline fuse. I suspect also that the fuse is to big. I am going to take a picture of the set up and post it along with the pump. I doubt the pump is damaged because once it starts running it works great and the voltage is around 13 on the meter. On a high power pump like this what size wire should I get? thanks all for your help
By Rod McInnis (rodmcinnis) on Wednesday, September 29, 2004 - 1:18 pm:    Edit Post Delete Post

You said that the voltage goes to zero. Where are you measuring the voltage at, the meter on the dash?

If the voltage to your dash goes to zero then I would say you have some serious wiring issues.

It could still be the pump. A typical D.C. motor has a commuator and brushes to make contact. It is not unusual for a motor to short out a portion of the rotor windings. When this section of the windings gets connected via the commutator to the brushes it can flow a LOT of current without developing any torque to help the motor turn.

If the motor is spinning the inertia will carry the rotor past the damaged winding and the motor continues to run. Draws a little more power and runs a little slower but it can still work okay.

The problem is when the motor stops with the damaged winding selected by the commutator. When you turn it on is simply draws lots of current and may not develop enough torque to start turning.

There could be other factors as well.

In general, a stalled motor draws LOTs of current. As the motor picks up speed it develops "back EMF" and the current draw is reduced.

Many loads, especially pumps, the load on the motor has sharp peaks. If the motor is running the inertia of the rotor will help carry the shaft past the peak and the pick up speed again once the peak passes. This allows the current load on the motor to average out. A problem can occur is the motor has to start against the peak load.

You mentioned that you have a reversing pump. If this is a flexible vane pump then the highest load it sees could be when the pump has to reverse direction and bend all the vanes the opposite direction. If the impeller is old and stiff it might be requiring more torque to bend the vanes over than the motor can deliver.

If you think about it, when you start the pump it is likely to be reversing. If the last thing you did was fill the ballast tank, the next thing you are likely to do is empty it. This would put a heavy load on the motor and it might not be able to handle it.

The problem gets worse if the wiring is not sufficient. If the motor draws maximum current, and the wiring won't handle it, the voltage at the motor drops. The lower voltage means less torque. Less torque increases the odds the the motor won't start against the high load.

I would start by figuring out the maximum current that the motor wants. If you know the brand and model we can probably look it up. The maximum current should also be printed on the motor body if you can get down to where it is and read it.

Once you know how much current the motor requires we can select the proper size wire to supply it. This will be a function of the current AND the length of the wire. Tell me how many feet it will take to get the wire from the switch to the motor.

The switch needs to be able to handle the current. Many switches are very limited and might not be suitable for the amount of current the motor requires. In such case you isntall a relay, which can actually simplify things some because the relay can be mounted closer to the pump and perhaps shorten the length of heavy wire you need to run. For example, if the pump is close to the engine the relay can be powered (through a fuse) from the main distribution point on the engine and the run can be a few feet. Small wire then runs up to the dash to the control switch (the existing wire would work fine, assuming the insulation hasn't been damaged).

If you are taking power from the fuse block or distribution point up by the dash then you need to make sure that the wiring to the dash can support this much additional current. If your volt meter drops to zero (or any significant drop) then it tells me that there is something wrong with the wiring to the dash.

Start by telling us the make and model of the pump and where you have it mounted.


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