More electrical musings...
- Thread starter bridaus
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dhays
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You have got a big project there but it sounds like you are making good progress.
Ventana
Senior Member
Good luck. I've been tracing electrical stuff on ours since we bought it last fall, and I haven't really even scratched the surface. Doing this for a living you would think I could just dive in and fix everything, but honestly I'm so tired of looking at marine electrical crap that by the time I'm home from work I don't have the patience. I do have a big box of parts with just about everything to build new panels for in the salon, but again there is the issue of time and ambition.
For our bow thruster, there is a separate battery under the forward berth. I think it is only charged by it's own AC charger, so via generator or shorepower, but our wiring looks worse than yours and I haven't traced that out yet. It's on The List.
My goal is to get away from running the generator, so I'm switching as much as I can away from AC and trying to decrease usage, but it is a slow process.
For our bow thruster, there is a separate battery under the forward berth. I think it is only charged by it's own AC charger, so via generator or shorepower, but our wiring looks worse than yours and I haven't traced that out yet. It's on The List.
My goal is to get away from running the generator, so I'm switching as much as I can away from AC and trying to decrease usage, but it is a slow process.
bridaus
Senior Member
Larry,
An aside to the issue at hand, you have AC and DC wiring in the same locker (the disconnect switch and the regulator on the AC side), that is a potential safety issue, and ABYC violation. If you can't move the DC switch to the DC side, it should at least be placed in an enclosure. Move the regulator to the DC side as well.
It's a violation to have AC and DC components in the same locker/space, as it is to run unsheathed AC and DC wiring in the same bundle.
If one of these wires overheats and the insulation melts, it could bring AC and DC into contact, which could result in AC current returning through the water.
Thanks for that! Both are an easy fix.
exmaggiedrum
Veteran Member
Separate thruster battery
I've installed a few and worked on more than a few bow thrusters. A separate battery is most often located at the bow thruster so that wire sizes don't have to be huge coming from the house batteries (usually much farther aft). Depending on the length and the amps required you could need 4/0 wire for a long run, or even more. This is expensive and hard to run sometimes.
One issue is that the thruster battery then needs a charge source. Since thrusters use a lot of power for just a very small time the total draw on them is small, just like starting motors with start batteries. So you can use a trickle charger or separate charger just for that battery.
If you want to use the house batteries to boost a weak thruster battery you would still have to have the bigger cables although you might get away with a bit smaller because the time in use is usually small. But that wouldn't meet ABYC standards and if you did run it for a long time it would overheat the too-small cables.
You could use a combiner to charge the thruster battery while charging the house batteries and the cabling could be sized for a longer but smaller amperage but if you tried to run the thruster by combining them and the cables were too small you could start a fire or melt something. But if you are in an intense spot and need a short burst from your house batteries you might get a way with it. Not recommended though. Fuses should be rated for the wire size and max amps, not the thruster size or battery size or anything else.
Regarding using a meter to find a parasitic draw, the best tool to start with is a clamp-on ammeter. You can find inexpensive ones easily now. Working as a marine electrician for several years I never put a meter set on "amps" in line with any circuit. You will blow up the meter if you are wrong about how big the amps are and you have to disconnect the circuit to do it anyway. A clamp-on meter is easy to use and it can be put on either the negative or the positive wire depending on what you are trying to figure out.
What I would do is turn everything off that you think is involved and then run around and put the clamp-on meter at each battery lead at each battery. When you find a draw that should be shut off you then have to go downstream with the meter to find the unswitched draw. It is not always as straightforward as you would think. You might find a big surprise that you would not have predicted.
You may have to turn on and off DC circuits at the panels to ID what is going on. It is trial and error. Sometimes it is easy and quick and other times it takes more work.
A handy design, and the one recommended for all boats, is to have a DC current shunt at the DC negative from each battery bank. The shunt has to be the very first thing after the battery DC neg with no other neg wires going to the battery around the shunt. The shunt is connected to a meter which will show all current going in and out of the battery. If you have everything shut off and the meter still shows a draw (aside from the meter draw) then you know all the time whether your wiring is set up the way you want or if something else will not shut off. More than a few times, a parasitic draw can be traced to a faulty alternator which has shorted out. This will show up on the meter (or dead battery). If so the alternator will be warm to the touch with the motor off. This is only one type of issue that a meter can help with.
But a clamp-on meter will pay for itself very quick after you learn the few basics. A fancier one will have a "max hold" feature where you can leave it on while you crank an engine or run the thruster and it will show how many amps max were used even if you are up at the helm to run things at the moment.
Just some ideas.
I've installed a few and worked on more than a few bow thrusters. A separate battery is most often located at the bow thruster so that wire sizes don't have to be huge coming from the house batteries (usually much farther aft). Depending on the length and the amps required you could need 4/0 wire for a long run, or even more. This is expensive and hard to run sometimes.
One issue is that the thruster battery then needs a charge source. Since thrusters use a lot of power for just a very small time the total draw on them is small, just like starting motors with start batteries. So you can use a trickle charger or separate charger just for that battery.
If you want to use the house batteries to boost a weak thruster battery you would still have to have the bigger cables although you might get away with a bit smaller because the time in use is usually small. But that wouldn't meet ABYC standards and if you did run it for a long time it would overheat the too-small cables.
You could use a combiner to charge the thruster battery while charging the house batteries and the cabling could be sized for a longer but smaller amperage but if you tried to run the thruster by combining them and the cables were too small you could start a fire or melt something. But if you are in an intense spot and need a short burst from your house batteries you might get a way with it. Not recommended though. Fuses should be rated for the wire size and max amps, not the thruster size or battery size or anything else.
Regarding using a meter to find a parasitic draw, the best tool to start with is a clamp-on ammeter. You can find inexpensive ones easily now. Working as a marine electrician for several years I never put a meter set on "amps" in line with any circuit. You will blow up the meter if you are wrong about how big the amps are and you have to disconnect the circuit to do it anyway. A clamp-on meter is easy to use and it can be put on either the negative or the positive wire depending on what you are trying to figure out.
What I would do is turn everything off that you think is involved and then run around and put the clamp-on meter at each battery lead at each battery. When you find a draw that should be shut off you then have to go downstream with the meter to find the unswitched draw. It is not always as straightforward as you would think. You might find a big surprise that you would not have predicted.
You may have to turn on and off DC circuits at the panels to ID what is going on. It is trial and error. Sometimes it is easy and quick and other times it takes more work.
A handy design, and the one recommended for all boats, is to have a DC current shunt at the DC negative from each battery bank. The shunt has to be the very first thing after the battery DC neg with no other neg wires going to the battery around the shunt. The shunt is connected to a meter which will show all current going in and out of the battery. If you have everything shut off and the meter still shows a draw (aside from the meter draw) then you know all the time whether your wiring is set up the way you want or if something else will not shut off. More than a few times, a parasitic draw can be traced to a faulty alternator which has shorted out. This will show up on the meter (or dead battery). If so the alternator will be warm to the touch with the motor off. This is only one type of issue that a meter can help with.
But a clamp-on meter will pay for itself very quick after you learn the few basics. A fancier one will have a "max hold" feature where you can leave it on while you crank an engine or run the thruster and it will show how many amps max were used even if you are up at the helm to run things at the moment.
Just some ideas.
Waywego
Veteran Member
A helpful tool for working on 12V systems is the PowerProbe. I have the PowerProbe III with 40' of power supply cable and you can add 20' more if needed. It is basically a DC volt meter coupled with the ability to ground or inject 12V (up to about 8A) through the tip of the probe. I sure wish I had one of these back when I was towing trailers all the time!
Xsbank
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Those posts are useful for connecting cables to lengthen them for a specific purpose but I would toss them and install bus bars. Those stacks are poor practice and can result in failures. One bolt for all those contacts?
Also, judging by the discolouration in there, humidity is an issue. Vent the area better and start checking all those wires for corrosion, a lot of it is untinned automotive wire and automotive crimps. Replace all of it!
Every circuit/system needs a fuse or a breaker to protect it and every device needs a fuse or breaker to protect it.
Nigel Calder’s bible is essential reading.
Also, judging by the discolouration in there, humidity is an issue. Vent the area better and start checking all those wires for corrosion, a lot of it is untinned automotive wire and automotive crimps. Replace all of it!
Every circuit/system needs a fuse or a breaker to protect it and every device needs a fuse or breaker to protect it.
Nigel Calder’s bible is essential reading.
Last edited:
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