Oversheeting involving RMG failsafe and bad battery or cell

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Oversheeting involving RMG failsafe and bad battery or cell

Postby s vernon » Mon Aug 05, 2013 8:34 pm

I have seen this twixe recently and lucked out as to the apparent cause a couple weeks ago. Another of our fleet members had it happen to him yesterday and I think I remember it happening to someone at Elon many years ago. A Florida friend told me the same symptons happened to him as well and it was a bad cell in the boat battery pack causing it.

So I will post this for people to keep in mind if they ever see something like this.

What I think is happening in most cases is that the RMG winch, which is set up in failsafe mode, senses low voltage due to high amps being drawn and a boat battery pack problem like maybe the battery getting a little low or a bad cell in the pack. The RMG, by design, sheets to slighlty more than half way in and sits there for a while. Then for some reason the RMG comes to life again and sheets in the other "half way plus" putting a pretty good strain on the sheets and on itself. And then it just sits there again. It does not matter where the sheet stick is on the radio.

In the first one that I saw and got lucky on, the sheeting and sitting was occurring when I moved the rudder stick, perhaps full throw. I am thinking there might have been binding in the rudder causing high amps which contributed to the low system voltage/RMG going into failsafe.

The cure for it was to put a known good (charged) battery in the boat. The "bad battery" actually had a slightly higher measured no load voltage than the "good battery", just to be aware of that wrinkle.

I guess this might be a another good reason not to use RMG failsafe. And to measure nimh battery pack voltage under load, looking for a bad cell.
Scott
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Re: Oversheeting involving RMG failsafe and bad battery or c

Postby Rick West » Tue Aug 06, 2013 12:02 pm

The Battery Limiter ("Fail Safe") option is part of the RMG set up. I thought most had this feature turned off for the last decade. Additionally, after the 2005 summer of the Phantom in the Bilge, the alternate wiring (RMG use manual) of the radio board became widely accepted. This mitigated loss of the RMG by separating the wiring for the RMG and the growing popularity of high torque servos. These servos presented better control downwind in a moderate breeze or gusts. High amp loads fakes a battery low voltage condition and the RMG will react to this event in a nano-second then check out okay when out of the water. Hence, the "Phantom."

The run can be a high load on the winch. Even higher loads occur rounding the leeward mark when sheeting in and high loads on the rudder are common.

The Battery Limiter feature is for battery failure and aids in getting the boat back to shore. This and standard wiring is not recommended for the EC12. Moreover, those of us sailing the J Class use two batteries in the wiring separation to provide voltage to the RMG during high amp draws. Battery failure today while in use is extremely rare.

A search of this discussion site should find those conversations.
...94 [8D]
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Re: Oversheeting involving RMG failsafe and bad battery or c

Postby greerdr » Thu Aug 08, 2013 10:27 pm

Ric nailed this!
Read the booklet Bob G sent with that winch.
Scott,you are a great skipper but not all of us can pull a boat from death and make her win as you do.
Your hints are super and I thank you for them.
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