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Old 22-06-2018, 14:19   #1
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how to install starting relay

Ok, my buddy has a Yanmar 3GM30 afflicted by the well-known voltage drop issue in the starting circuit. Apparently the standard fix is to add a relay. The yard sold him a relay to fix the problem, but didn't give any guidance on how to install it. Pic shows the existing wiring, and the new relay that needs to be fitted.
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Old 24-06-2018, 01:46   #2
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Re: how to install starting relay

You will need to wire the new relay in series with the existing Starter solenoid input (the White wire)
Hopefully the attached will explain this.
Essentially, mount the relay as necessary, closer to the Start the better. It sounds as though it is internally earthed through the case? so if not mounting on the Engine, you may need to run an earth back to the Engine or suitable -ve connection.

Check the small green wire is the control input for the relay. Should be a circuit from this to the case or the -ver terminal of the new relay.

The White wire on the Starter will probably be the control Input from the Starter key switch or Push button. You can confirm this by operating the switch and check for voltage on this wire.

If this is correct, disconnect the White Wire (from Starter motor) and connect to the Green wire on the External relay (new Relay). When you operate the Starter key switch, you should hear the new relay click.

You will need to run a small (say 2.5mm2) wire from the terminal which has the large red cables connected. This should be the Battery supply to the starter, to one of the posts ( I assume these are some type of terminal) on the new relay.

From the other post of the new relay, connect a wire to the place where the old white wire was on the Starter Motor.

if the cable to the new relay needs to run any distance or could be damaged, you may want to consider fuse protection. This is only for Short circuit protection so a 15 or 20A fuse would probably do
Hope this helps
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Old 24-06-2018, 10:21   #3
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Re: how to install starting relay

There are 2 issues here. First is that the current run from your key switch down to the solenoid needs cleaning up. That pathway may not be strong enough to get the solenoid to snap closed and allow high starting current into the starter motor. If the thin wire run from key is good, and the starter just clicks a bit on key turn, then it's the high current run that needs attention.

How many amps does the relay you bought say it will handle? If 15A then it is for installing in the key-to-solenoid run. If it says 40-60-80A it's meant to bypass the solenoid (which is a relay in part). Wiring in each case is very different.

Cheap testing trick is to tap lightly on the solenoid while someone turns the key. If it spins normally then the solenoid is sticking and while a small 15A relay can bring more current to the solenoid, you're not actually solving the root cause.
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Old 24-06-2018, 17:05   #4
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Re: how to install starting relay

Dymaxion, I agree with what you say, however, as the OP states, "Yanmar 3GM30 afflicted by the well-known voltage drop issue in the starting circuit". If this is a well known problem, perhaps Yanmar have an issue with their starter motors?
I would think the root cause is the size of cable Yanmar (and most others) use in the control wiring. This being the case, the real solution may be to rewire the start solenoid with a larger cable, but not practical. Hence the simple? fix of an additional relay.
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Old 24-06-2018, 17:24   #5
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Re: how to install starting relay

Quote:
Originally Posted by Ding Duck View Post
Dymaxion, I agree with what you say, however, as the OP states, "Yanmar 3GM30 afflicted by the well-known voltage drop issue in the starting circuit". If this is a well known problem, perhaps Yanmar have an issue with their starter motors?
I would think the root cause is the size of cable Yanmar (and most others) use in the control wiring. This being the case, the real solution may be to rewire the start solenoid with a larger cable, but not practical. Hence the simple? fix of an additional relay.
IMO, the root cause is lack of maintenance of the electrical harness.
You are correct that there is general perception the control wiring is too small but IME, the problem is corrosion build up in the connectors of the harness and allowing sea water ingress to the connectors.

I note that Yanmar did originally place one of the harness interconnects in a poor position that made it difficult to keep the water away from it but I understand this has been moved in later years.

Clean and if necessary replace corroded connectors, coat with a dielectric grease (like DC-4) and the original Yanmar wiring works.

The addition of another relay is a quick and dirty fix but I do accept that it works.
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