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Old 05-12-2019, 03:14 PM   #1
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More electrical: Helm tied to bow thruster... huh?

Noticed yesterday on a cruise to Newport for lunch (was gorgeous out), that whenever I ran the bow thruster, the VHF radio would complain about low voltage. At the same time, the house battery was being charged properly... therefore I surmise:

The bridge (or maybe just the VHF radio) is wired to the bow thruster battery.


Is this in any way normal for any boat? For a KK42?

I'm betting not, and I'm betting it's another in a long line of "just make it work" wiring issues I'm finding.

Thoughts appreciated on what should be normal here.
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Old 05-12-2019, 03:58 PM   #2
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Greetings,
Mr. b. "Is this in any way normal for any boat?"





I think your "just make it work" observation is an accurate assessment. My own wiring "expertise" is marginal, to say the least, but like many, many other TF members, I've seen my share of WTF's in the wiring department.


Yet another good reason to take some time to either make your own diagram of your wiring and/or clean up what's there.
I'm hoping to do some electrical remediation in the near future. Trace and label.
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Old 05-12-2019, 04:56 PM   #3
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Do you know for sure that you have a separate bow thruster battery? Your thruster may be powered off one of the start batteries or the house bank. No way to tell except trace the wires and see where they go. If it is off the start or house bank it may be drawing that battery down enough to cause low voltage on the VHF. I would think it is unusual to wire a VHF to a thruster battery but I have seen unusual things before. Do you have a good understanding of the boats wiring? If not now would be a good time to investigate and see what is powered by which batteries. Good luck.
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Old 05-12-2019, 06:24 PM   #4
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I am about 10% through tracing all the "new" wiring. I trust the original KK wiring and have schematics of sorts for it.

I do, for sure have a bow thruster battery.

If it was wired to only one of the house batteries, the VHF wouldn't chirp at me when I hit the bow thruster, but all the time. I'm 99% sure it's connected to the bow thruster battery. The only thing I don't know is if the entire bridge/helm is connected to it, in which case I'm "low volting" all sensitive electronics which is not good. I will be investigating more, but so far I'm hearing this is a bad idea.

PS: Thinking about it, I'm positive this is a horrible idea, as the bow thruster is high power draw, and hooking electronics to that battery is asking for trouble.
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Old 05-12-2019, 06:33 PM   #5
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Have no separate battery for the bow thruster and presume its power comes from the house batteries, but haven't experienced your issue since operating a radio while making delicate maneuvers with the thruster has not been attempted.
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Old 05-12-2019, 06:39 PM   #6
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Quote:
Originally Posted by markpierce View Post
Have no separate battery for the bow thruster and presume its power comes from the house batteries, but haven't experienced your issue since operating a radio while making delicate maneuvers with the thruster has not been attempted.
House banks are usually bigger than bow thruster banks (therefore less voltage drop).

Plus my batteries are all a bit weak, none (except the engine battery) tested over 65% SOH.

It's instructive of you to point out that some bow thrusters are tied to house. I would think that means either you have a smaller thruster, OR a big ole house bank and associated cabling.

PS: Wasn't operating my radio, it was just on and then chirped at me about low voltage. It's a Uniden, maybe it's also more sensitive than others, or has a low voltage warning "feature"...
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Old 05-12-2019, 07:19 PM   #7
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Well if you do have a dedicated battery for the thruster, I would move any electronics off that battery and to your house bank. I have a dedicated battery for my stern thruster but I have never measured the voltage when the thruster has been actuated so I really donít know what it drops to. Our boat has a seperate breaker panel on the bridge but it does not have adequate wiring to it. Our VHF would complain about low voltage at times so I ran new cable to the bridge and added a seperate panel just for the electronics. I went oversize on the cable so I get really good voltage on the electronics. I left the other things on the OEM panel and now that the electronics are off the old panel the voltage on the old panel is much better.
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Old 05-12-2019, 07:24 PM   #8
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Greetings,
Mr. b. A thought...Disconnect everything from your thruster battery and see what still works. Any upper helm stuff affected?
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Old 05-13-2019, 06:52 AM   #9
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If you have a thruster battery, itís important to know how itís connect to the house bank.
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Old 05-13-2019, 09:57 AM   #10
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Quote:
Originally Posted by Comodave View Post
I have a dedicated battery for my stern thruster but I have never measured the voltage when the thruster has been actuated so I really donít know what it drops to.

Well I have measured the voltage at my thruster batteries and it drops when activated...mine was to 9.ĒsomethingĒ volts. Some of that is related to battery health perhaps, but I would think itís not a good idea to have a thruster bank powering other electronics.
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Old 05-13-2019, 01:11 PM   #11
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Mine will go down to about 10.4 or so...

I stopped by boat at lunch, turned off battery switch on thruster battery, VHF still worked. Then I disconnected the battery, stopped working. So the power is tapped off prior to the switch but after the battery terminal.

Next steps: With battery disconnected, see what else has stopped working, then try to find the entry point for the bow thruster power to the helm.
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Old 05-20-2019, 02:42 PM   #12
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Again, I feel your pain. Our thruster battery is separate, but at some point a PO moved the wheelhouse electrical panel feed from the house bank to the start bank, so every time you start the main, all the electronics reset. Fun.
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Old 05-20-2019, 02:57 PM   #13
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My bow thruster batteries are separate from house and engine start banks. They consist of 4- 6v golf cart batteries and their own charger. A simple SOC meter ($9.00 on Amazon) tells me how healthy the thruster bank is.
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Old 05-20-2019, 03:15 PM   #14
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Guess what I was doing today...
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Old 05-20-2019, 03:38 PM   #15
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It may not be that the radio is connected to the thruster battery. That would be really strange but of course not out of the question.

My bet would be the radio and the thruster circuit share a mutual negative buss/connection somewhere that has a poor connection or is undersized and is creating the voltage drop under load.
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Old 05-20-2019, 03:44 PM   #16
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I see a pile of old cut out cable ties but where is the pile of old, disbanded, undersized, non marine style wire? Every time I get into my wiring there is always a pile of that too! Though most has been cut out at this point.

I especially enjoy finding circuits powered by speaker wire and the like!
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Old 05-20-2019, 03:48 PM   #17
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Quote:
Originally Posted by Duvie View Post
My bet would be the radio and the thruster circuit share a mutual negative buss/connection somewhere that has a poor connection or is undersized and is creating the voltage drop under load.
Great second thing to check for...

I do still think it's a positive hookup because of the mess, but very possible it's a negative buss, will check as well. thanks!
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Old 05-20-2019, 03:50 PM   #18
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Quote:
Originally Posted by Duvie View Post
I see a pile of old cut out cable ties but where is the pile of old, disbanded, undersized, non marine style wire? Every time I get into my wiring there is always a pile of that too! Though most has been cut out at this point.

I especially enjoy finding circuits powered by speaker wire and the like!
That was ten minutes I had at lunch. I actually don't see a lot of undersized (surprise), just OLD and way too pliable.
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Old 05-20-2019, 04:03 PM   #19
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The other thing that I always do when working on the wiring is removing the old tie wraps. If I add a new wire I will tie wrap it to the bundle then I will cut out all the old ties. I hate it when trying to follow circuits and there are six layers of tie wraps in the bundle!

Keep chopping!
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Old 05-24-2019, 01:09 PM   #20
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I absolutely agree with all the comments about being certain NOTHING but the thruster works of that battery,

There is a different issue here, however, and that is alternative power source for the VHF itself.

You can buy for 100 to 200 what campers call a "generator" but is actually a high capacity Lithium battery. These can charge form 12v as well as solar or 110. They can be wired into your main 12 v circuit. Then you can wire the VHF and other low amperage electronics directly to the "generator."

This achieves several things
1. the radio now gets "pure" 12v, free of variations caused by your alternator
2. If you need to power down everything else because of some issue ..eg smoke coming from the engine room, the vHF will still work.
3, These generators have built in 110v inverters and USB jacks that can supply your cell or other USB 5v powered devices.
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