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Electrical Conundrum

Cardo

Member
Hey Everyone,
I have a strange electrical issue that has me stumped. I have noticed this situation on two separate circuits: bilge pump and radar. When hooked up to shore power, both function correctly. When on battery power only, the bilge pump works at a much slower pace and the radar dome does not function at all.
These two units are on separate curcuits and no other circuit or unit on the boat seems to be affected similarly.
I have load tested the batteries and all are good. Power is getting to all units.
Any insight on why this may be happening or what to test next?
Thanks in advance,
Rich
 
Hi Rich - how did you load test your batteries? Are these circuits the ones with largest draw/load on your boat?
-Mark
 
Hey Mark,
I load tested the 3 batteries individually with an automotive load tester, the one with the heating element.
These may be two of the largest draws, however the isssue occurs if each is the only curcuit drawing power.
Rich
 
Other members (like Jim Cleary who is an actual electrician!) might have some better ideas …

But if the batteries are already proven to be able to handle the load, I would start looking for faulty connections. I would apply the load then run around with my thermometer gun and see who is getting hot. Or measure voltage drop across connections. Or turn power off & use my ohm meter to hunt for resistance.

I’d hunt in both the positive and negative legs since it could be either one.

One of Nigel Calder’s big themes is that stainless steel is a bad conductor. And people often put stainless “in the circuit” as washers or nuts. They can be used as fasteners, etc as long as they aren’t in the circuit. He had an example of a boat owner who used a stainless nut & washer between two ring connectors and they got so hot they fried some flesh.

I think something like that could be a big enough draw to keep a bilge pump or radar from being happy & productive.
 
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Check the wires, they may have common wire not thick enough, and you may have to big voltage drop. Bilge pump and radar are big current suckers.
 
The strange clue, though, is they work fine when plugged into shore power. So, when getting fed from the battery charger, it’s fine.

I’d maybe focus first on the connections & cables between the batteries. If those were faulty or undersized the radar & bilge pumps could misbehave, but maybe they are being fed more directly from the battery charger.
 
First test, on the pump because it's easier to access. With shore power disconnected. Disconnect the pump, as close to the pump as possible. Disconnect both the positive and negative wires.

Turn on the pump circuit. Measure the voltage at the disconnected pump wires. Also measure the battery voltage. They should both be the same, about 12.6v.

Now, connect the pump, in a way you can still measure voltage there. Like, just temporarily twist the wires. Repeat the 2 voltage measurements. If you still have 12.6V at the battery, but less at the pump, then you have a connector or wiring problem. If the battery voltage is low, then a battery problem.

Assuming everything else works (can you transmit on VHF, and are you received at the other end clearly?) Then it's likely a connection problem. Since radar is affected also, look at the ground wires, and look at where they might be in common. Could the ground for the radar be sliced to the ground for the pump? Maybe in the bilge on the way to the base of the mast?

Let me know what you find, and I can give some more ideas/tests.

You could also repeat those tests for the radar, but would need to go up and down the mast half a dozen times.
 
The strange clue, though, is they work fine when plugged into shore power. So, when getting fed from the battery charger, it’s fine.

I’d maybe focus first on the connections & cables between the batteries. If those were faulty or undersized the radar & bilge pumps could misbehave, but maybe they are being fed more directly from the battery charger.
It is odd, but not unexplainable. And I can imagine ways for them to work on shore power by both a bad connection or bad batteries.
 
Rich

Is this a problem that has recently became an issue? Meaning, have these circuits worked fine in the past? If so It probably means there is a high resistance somewhere in the circuit wiring from the batteries out to those devices. I would start at the batteries and work out in the direction of the pump and radar and remove and clean ALL the connections to locate a source of corrosion. Remember, a connection may look perfectly clean and free of corrosion, but it could still be the source of the problem.

Jim
 
Thanks for chiming in, Jim.

I first noticed a subtle difference in the performance of the bilge pump. The radar became an issue last season. The fact that only these two systems seem affected supports the connection theory that you Mark brought up, and Warren's thought about a common ground connection.
I'll get at some tracing and voltage testing this weekend. Hopefully, I'll find something!

Thanks again, guys!
 
Don't discount the possibility that the 2 issues are unrelated. It isn't uncommon, when wiring gets old, for a whole bunch of connectors to all fail about the same time. I made a lot of money off another sailor this past season, fixing something new every 2 weeks. Radar, interior lights, VHF, lift pump, navigation lights, autopilot. All the same issue, just different ring connector that failed each time.
 
Carlo, I'm a negative guy:
The 12v wire circuit negative grounding point is a busbar in the engine compartment. Access through the quarter berth access hatch. It is subject to possible splashing from the prop shaft. Over the years, much new work gets grounded there. A small gauge wire goes from the tiny busbar to the engine block. Mine was green, wire connections corroded. I redid everything new & larger, including cleaning the block grounding point from both harness & battery, coating all with anti-corrosion goo. The juice has to get home!
 
Dave,
I replaced the busbar in the engine compartment and redid all connections including using the compound that Jim Cleary suggested.
I also replaced a busbar connected to the bilge pump. I am in the process of redoing all those connections.

Warren,
My MFD reads 12.6 V at the unit as the battery. I did a resistance test for the radar cable that was suggested by Raymarine. The cable reads the correct resistance. This seems to indicate that the issue may be in the radar dome itself.
There is a voltage drop at the bilge pump to about 10 V. I will continue to trace connections for this issue. The Auto switch is on the main panel and the manual switch is in the cockpit.

As Jim said, all connections should be suspect!
Thanks again, guys!
 
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