Livewell fill pump wiring idea - opinions?

[jtexas]

Typical livewell fill pump, through-transom intake - who among us hasn't burned one up by forgetting to turn it off while underway?

The other day it occurred to me - if I connect the ground from the pump to my outboard kill circuit, the pump will go off when I start the motor, and come back on when I shut it off.

I can't have been the first person to think of this, so.....why isn't it common practice? I mean, why shouldn't I do this?

thanks!

 

[WillyBWright]

Re: Livewell fill pump wiring idea - opinions?

You shouldn't do it because one side is grounded all the time and it wouldn't shut off with the key. The other reason is that it'll provide a path to the motor 230v kill circuit through the 12v DC motor and leave you with no spark and/or a seriously fried pump motor when you connect it to the ungrounded side. BUT ... If you happen to have a motor where the ignition gets it's power from the battery instead of making it's own ignition power, it would work. It would work in my boat because I have amplified battery ignition, but I'd have to put in a magneto style ignition switch (like most outboards have, but mine doesn't cuz it's a morphodite).

But you gave me a great idea when I go to re-do the interior of my closed-bow V-hull. Right now i have two 6 gallon portable gas tanks. I'm going to make a 3/4-width bench seat for the back so waterskiers getting in don't have to step on the seat. I was going to put one of the tanks in there as a spare and put a permanent V-shaped tank in front. There's room under the rear deck where the skiers get in for the spare tank. That bench seat is now going to house a livewell and I'm going to get me one of those newfangled outboard key switches and wire the pump just like you said. I guess sometimes it pays to own a morphodite. Thanks!

 

[jtexas]

Re: Livewell fill pump wiring idea - opinions?

yeah, I see how that could be a problem..........a mo betta electronican than me with some formal training might be able to find a way to make it work, but I'm gone have to do it the hard way, I think one transistor, a couple resistors and the purple accessory wire might do the trick.......................

 

[dingbat]

Re: Livewell fill pump wiring idea - opinions?

A simple relay would work. My trim tabs automatically retract when I turn the key off so I don't see why you couldn't use a similar setup to run your pump.

I have a scoop intake on the bottom of the hull for my livewell so I got the opposite problem. My livewell / storage fills with water if I don?t close the valve on the intake and many a lucnh have been found floating becouse of it

 

[Barnacle_Bill]

Re: Livewell fill pump wiring idea - opinions?

If you can find a normally closed 12V relay you could run it off the purple wire. Key off - ground completed, key on - ground opened. Radio shack maybe?

 

[PondTunes]

Re: Livewell fill pump wiring idea - opinions?

yeah, I see how that could be a problem..........a mo betta electronican than me with some formal training might be able to find a way to make it work, but I'm gone have to do it the hard way, I think one transistor, a couple resistors and the purple accessory wire might do the trick.......................

You're on the right track with the accessory wire. A standard 5 wire bosch relay will do the trick.

*IF* you're trying to use the purple wire it probably is a ground. In this case you should connect 86 to your purple wire, and 12v + to 85. Terminal 87 should still be grounded elsewhere (NOT to the purple wire as it only has ground when the key is on)

What this will do is apply a ground to terminal 85 when your accessory circuit is live.. This will energize the relay and break the connection from 87A and 30 and turn off your bilge pump. When you switch off the accessory circuit the relay will close and the bilge pump will resume normal operation.

 

[jtexas]

Re: Livewell fill pump wiring idea - opinions?

actually this is what I was thinking...relay sounds easier though.....

 

[jtexas]

Re: Livewell fill pump wiring idea - opinions?

At least, the bench test was successful.
I decided the relay was too easy.

Here's what the finished product looks like:

Pretty ugly, huh?
Couldn't be bothered with circuit boards and all that.

Resistor values in the original circuit were way too high, also added a flyback diode. Here's what I ended up with:

Thing is, I'm not sure the power transistor will draw 3 amps, so a clogged pump won't blow the fuse. And since I switched over to blade-type fuses, can't find a 2-amp. Might have to do it again.

 

[bruceb58]

Re: Livewell fill pump wiring idea - opinions?

The power transistor will do fine with 3 amps. Problem might be the power dissipation the way you have it in epoxy like that.

 

[jtexas]

Re: Livewell fill pump wiring idea - opinions?

I mis-articulated my concern...........the base current is about 45ma, which I believe (could be wrong) will yield just over 2 amps across the load.

Honestly I thought I was well enough within the limits of the 3055 to avoid heat-related issues......might have to mull it over a bit.....................

I'm really a total hacker when it comes to stuff like this - no training, just like to dabble.

 

[bruceb58]

Re: Livewell fill pump wiring idea - opinions?

You should just overdrive the base and the current will end up being whatever the load will end up driving since you will be in saturation. Assuming your pump draws around 3 amps when it is running and a collector emitter voltage of around 1V(according to the data sheet), you will be dissipating 3 watts across that transistor. You should really try to find a power mosfet that has a lower VCE(drain/source in a FET) voltage...less dissipation that way.

 

[jtexas]

Re: Livewell fill pump wiring idea - opinions?

pardon my ignorance.........dissipating 3 watts, in practical terms, is that wasted energy? How much more of a drain am I placing on the battery, over just running the pump?

Looking at info on power mosfets, I see Vds listed in ranges like, 70 or 100, don't really know how to evaluate these, do they typically give the voltage at saturation? I don't expect you to type out a complete primer on transistors or anything, I appreciate whatever suggestions you might have.

Parts availability being what it is (Radio Shack being just down the street) I'm tempted to do this over again eliminating the 50Ω and dropping the 220 down to 168Ω or so.......and maybe a heat sink.

thanks!

 

[bruceb58]

Re: Livewell fill pump wiring idea - opinions?

Since the data sheets list the VCE of 1V at 4A, the power pissipated through the transistor while current is lowing would be V*A or 3W in your case. This is wasted power while the pump is on. Not enough to worry about battery wise.

Just do what you are planning on doing by driving the base a little harder and maybe put a heatsink on it. You will be fine.

VDS is the max voltage that you can put across the drain and the source. In this application it would be whatever the battery voltage is. Typically MOSFETS list the "on" resistance. This will help you calculate the voltage drop across the device with a given current using ohms law.

A good MOSFET for this would be an IR530. Has an on resistance of 0.16 Ω. The part you are using is double that. If you really want to overkill it, use a IRF150...tons more current capability and an on resistance of 0.055Ω