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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems > Voltage Drop Problem: battery, wiring or both
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Thread: Voltage Drop Problem: battery, wiring or both Reply to Thread
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Topic Review (Newest First)
08-09-2014 01:08 PM
MarkSF
Re: Voltage Drop Problem: battery, wiring or both

Found a new, geared starter on Ebay for my Kubota, for $80. It's half the size and weight of the old one. The reduced size helps because the bolts are now kind of accessible. (they weren't at all, before)
08-08-2014 08:33 PM
Capt Len
Re: Voltage Drop Problem: battery, wiring or both

Take an old solinoid apart to see that the two bolt ends that are the terminals are corroded. More important is the copper end of the moving part. When it pits up too bad it may or may not connect across the bolt ends and can be temp sensitive. (Click,click) If you turn it 90 degrees you can get some more life out of it .That's pretty haywire. but I've done it in the snow up a logging road.
08-08-2014 08:03 PM
travlineasy
Re: Voltage Drop Problem: battery, wiring or both

I strongly suspect the problem is with the starter, thus explaining the higher than normal voltage drop and battery load-down. Marine starters are not any different that an automobile starter. There's nothing to prevent corrosion causing moisture from getting inside, and in the damp environment of a boat's engine compartment, it doesn't take long for the process to begin. The only method I know to control that environment is to install a good ventilation system, which in my boat is a 72mm computer fan that runs pretty much constantly, but uses very little electricity. It draws just .04 amps, but it moves a lot of air at 12 CFM. Since that fan was installed, my engine room corrosion problems have ceased to exist. The fan cost me a whopping $7 from Amazon.com.

Good luck,

Gary
08-08-2014 06:37 PM
MarkSF
Re: Voltage Drop Problem: battery, wiring or both

Quote:
Originally Posted by mitiempo View Post

Now if there are glow plugs and they are powered off the panel a relay does make sense as they do use a lot of current.
My Universal was wired so that the start button is only energised via the glow plug switch. The problem with that is, you have the glow plug current dropping the starter solenoid voltage!

I have rewired it so the two are separate.
08-08-2014 06:35 PM
MarkSF
Re: Voltage Drop Problem: battery, wiring or both

Quote:
Originally Posted by mitiempo View Post
I disagree. The starter solenoid doesn't use much current. That is why there is a solenoid there to start with. If the voltage at the solenoid isn't as high as it should be there is a wiring problem to or from the panel, either gauge, connections corroded, or age of wire. Adding a relay (really another solenoid) will not solve the problem only mask it and add more connections at the same time.

Now if there are glow plugs and they are powered off the panel a relay does make sense as they do use a lot of current.
I agree. The starter solenoid IS a relay. So you're adding a relay for a relay. Will that relay need a relay too?
08-08-2014 06:34 PM
MarkSF
Re: Voltage Drop Problem: battery, wiring or both

I've spent quite a bit of time trouble-shooting an intermittent no-start problem, that only occured after the engine had been heat-soaked (ie, re-start an hour after shutdown). The solenoid went click, but the starter did not spin up.

There are many things that can go wrong.

1) You need a healthy voltage to activate the solenoid. This is down to the ignition switch and wiring.

2) You need a healthy voltage at the starter main terminals. This depends on the cabling, battery switch, and starter battery.

3) You need a healthy starter motor.

Firstly, you need to systematically measure the voltage drops in your system. The starter motor needs at least 9V, ideally 10. You need to measure the voltage at the starter terminals WHILE CRANKING.

For voltage drops, connect the meter between battery + and starter +. Then repeat for battery - and engine ground. Again, measure while cranking. Please note that the losses on + and - sides add up.

Good cabling and battery switch should give you a 1V drop or less. A good battery should hold up to 11V while cranking, leaving you a healthy 10V at the starter.

In my case pretty much everything was wrong. Poor battery cables, an ageing 1-2-both switch, weak battery, ageing ignition switch, poor quality wiring to the solenoid.

So I now have new 2/0 battery cables from Genuinedealz.com, a new ignition switch, new wiring to the solenoid, a new 1-2-both switch from Blue Sea Systems, and a new group 31 battery from US Battery. Very healthy voltage at the starter now.

But guess what? The intermittent start problem was still present. I replaced the starter motor, all is good so far. Will need 6 months of use before I declare it fixed!
08-08-2014 12:01 PM
Don0190
Re: Voltage Drop Problem: battery, wiring or both

a relay only adds a couple of feet of wire

but if the problem is a bad connection from the switch to the solenoid in time the relay even wouldn't get power (still worth having the relay for times when starter battery voltage is at it's lower limit)
08-08-2014 10:59 AM
Vasco
Re: Voltage Drop Problem: battery, wiring or both

Quote:
Originally Posted by mitiempo View Post
I disagree. The starter solenoid doesn't use much current. That is why there is a solenoid there to start with. If the voltage at the solenoid isn't as high as it should be there is a wiring problem to or from the panel, either gauge, connections corroded, or age of wire. Adding a relay (really another solenoid) will not solve the problem only mask it and add more connections at the same time.

Now if there are glow plugs and they are powered off the panel a relay does make sense as they do use a lot of current.
I agree the problem is from old wiring. But rather than change out the wiring harness it's much easier to install a relay. The relay does not mask the problem it fixes it without having to get a new harness. As I said in an earlier post you might try cleaning all the contacts first.

As for the relay in some newer Yanmar installations a relay is already installed.
08-07-2014 11:16 PM
mitiempo
Re: Voltage Drop Problem: battery, wiring or both

Quote:
Originally Posted by Vasco View Post
It's for the engine control panel wiring. Installing a relay between the panel wiring and the solenoid will boost the voltage and it'll start every time you push the button.
I disagree. The starter solenoid doesn't use much current. That is why there is a solenoid there to start with. If the voltage at the solenoid isn't as high as it should be there is a wiring problem to or from the panel, either gauge, connections corroded, or age of wire. Adding a relay (really another solenoid) will not solve the problem only mask it and add more connections at the same time.

Now if there are glow plugs and they are powered off the panel a relay does make sense as they do use a lot of current.
08-07-2014 08:25 PM
preservedkillick
Re: Voltage Drop Problem: battery, wiring or both

Quote:
Originally Posted by hellosailor View Post
If you take a known good battery, and jump it directly to the starter with short fat jumper cables, that will tell you if the problem is internal to the starter, or out in your wiring.
This sounds like a good idea, thanks!
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