Wire bilge to 2 different batteries?

[Cougar_15]

I've had an interesting idea but I'm not sure it will work so I wanted to get some opinions from those who know about electrical wiring. I'm planning the new wiring for my restoration and I'm thinking about going with 2 sets of switches to keep the length of the wire runs as short as possible since I'm going to be changing the location of the deep cycle battery to under the port side passenger seat. I'm planning on getting an automatic bilge. When it's in automatic mode I want it to draw from the house battery (deep cycle), in manual operation I have no preference which battery it draws from. If I put the switch for the bilge on the dash I will have to run the power lines around 3/4 of the boat to get from the battery to the pump.

So my idea (sorry for the long lead up) is to put a switch for the automatic operation in the port switch box to be powered from the house battery and a switch for the manual operation on the dash to be powered from the starting battery (which is on the starboard side). So it would use 2 shorter runs rather than one long run. The idea being that while the boat is in use the automatic will be turned off and will use manual if needed and while at the dock I'll switch on the automatic.

Will this work? Will there be any problem with having the pump connected to the ground of both battery's but only drawing power from one of them? The 2 batteries are not going to be connected in any way.

 

[Silvertip]

Re: Wire bilge to 2 different batteries?

You are defeating the purpose of the automatic feature. Many times the bilge can take on water without you knowing it. Use the feature as it is intended. If the two batteries do not have the ground terminals interconnected, your idea won't work anyway. Current needs a complete path from the same battery.

 

[Cougar_15]

Re: Wire bilge to 2 different batteries?

I understand what your saying about the purpose of the automatic feature but my need for it is somewhat limited. My boat is trailered and most of the time will only be in the water for a day or a weekend with frequent use so the automatic feature is really not needed. Once in a while we plan trips to the cottage for 2 weekends in a row and it's easier to leave the boat in the water rather than drag it back and forth. Since no one will be there to monitor what goes on, this is when I would use the automatic feature.

With regards to the wiring what I was envisioning is both a positive and negative connection to each battery with both of the negative wires (one from each battery) connected to the negative wire on the pump and the positive from one battery to the manual lead and the positive from the other battery to the automatic lead. So the pump will have a complete circuit but what I don't know if there would be a problem with the negative from one battery being connected to the negative of the other battery by both being connected to the same lead on the pump...?

 

[trendsetter240]

Re: Wire bilge to 2 different batteries?

I understand what your saying about the purpose of the automatic feature but my need for it is somewhat limited. My boat is trailered and most of the time will only be in the water for a day or a weekend with frequent use so the automatic feature is really not needed. Once in a while we plan trips to the cottage for 2 weekends in a row and it's easier to leave the boat in the water rather than drag it back and forth. Since no one will be there to monitor what goes on, this is when I would use the automatic feature.

With regards to the wiring what I was envisioning is both a positive and negative connection to each battery with both of the negative wires (one from each battery) connected to the negative wire on the pump and the positive from one battery to the manual lead and the positive from the other battery to the automatic lead. So the pump will have a complete circuit but what I don't know if there would be a problem with the negative from one battery being connected to the negative of the other battery by both being connected to the same lead on the pump...?

No there is no problem with connecting the two ground terminals.

Further to what Silvertip said, the ideal setup would be to run the positive and negative pump wires directly to the house battery. Then you run the 3rd pump wire to the switch in your console so you can turn the pump on/off when you want to.

If the pump is small and draws only 5 to 8 amps you can run 14g wire which is not expensive.

 

[Home Cookin']

Re: Wire bilge to 2 different batteries?

bilge pumps don't use that much juice anyway.* Keep it simple; fewer places to fail.
Alternative is to hook up a bilge pump to each battery, with the float on one set higher than the other.
You'll find you seldom use the manual if you have a float; if you get any water while operating, it will kick the float when you take off.
To help preserve your battery life, rig the float so that a bit of water will accumulate before it kicks on. Many are set this way. And get a float that is encased in a box; your system can fail if something falls across an unshielded float.

*if someone launches your boat without the plug on a Friday night, the pump will run well into Saturday morning before it quits. I'm not saying anything else.

 

[Proselect]

Re: Wire bilge to 2 different batteries?

I agree to keep it as simple as possible. Your idea, however, will work the way you want. No damage will be done sharing the grounds as long as they are grounded to both batteries. Your idea makes sense, but I like the suggestion of just running the 3rd wire to operate the pump manually. I also understand where you are coming from, so if that is the way you want it for your convenience then no problem.

 

[Cougar_15]

Re: Wire bilge to 2 different batteries?

Thanks Guys, great advice as always...

 

[bruceb58]

Re: Wire bilge to 2 different batteries?

The draw back I can see with using two batteries is that if the deep cycle had that auto switch to it and your battery selector was pointing to your other battery and both auto switch and the manual switch were on at the same time, you would essentially be connectiing both batteries together through the bilge pump switches. If one battery was a lot more discharged that the other, you could be sending a ton of current through the bilge pump wiring and blow your fuse.