Mariner 8 hp two stroke problem – Charging

[GART]

My set up worked fine until I had cooling problems earlier this year, the engine overheated and I have been having various problems since.
I charge the battery (20 Ah Lead acid deep cycle no “liquid” acid but damp woolly stuff). By solar power & outboard engine with built in rectifier. I “boiled” the battery after only about 20 minuets motoring; the ammeter was only reading 1.5 – 2.5 amps. The 5-amp fuse did not blow. Although a sunny day the solar panels are only 3w and go through a controller to stop overcharging.
I was also trying out an Autohelm 800 at the time, it is possible something is wrong with it, it did stop working, that is when I discovered a locker full of battery gas and fumes coming out from the battery! The outboard no longer had an output, upon checking the earth wire from the rectifier to earth had not only melted the insulation on the wire, but the wire itself had disintegrated.
I have made a new connection to the earth, but still does not charge, there is AC coming out from the charging coil, but very strange readings the other side of the rectifier. On an analogue meter there is nothing, on a digital meter there could be 18v but only on the 50vDC range nothing on the 20v range, and it does not matter which way I connect the wires (normally I get a – if connected wrong way round).
Probably a new rectifier is needed, Maplin seem to sell lots of rectifiers for under £1, I expect a new Mariner one will cost £50+

Can anybody advise which Maplin Bridge rectifier I would need, or point me to a circuit diagram?

Secondly any ideas what caused it to go wrong in the first place?

 

[VicS]

Crumbs!!!!!

What is the DC output of your engine? either amps or watts.

Do you know if it is regulated. I doubt it but it might be.

How many connections are there to your rectifier. If just two wires from the coil, a +ve and a negative (earth), then you will probably be able to use a Maplin Bridge rectifier. 50 V PIV should be adequate but you'll need one with an adequate current rating. They do one rated at 10 amps which will probably be OK subject to your "generator" not producing more than that (or 120 watts) It may be have to be mounted on a small heat sink though. I'm looking at type KBPC10005.

You will have to keep your fingers crossed that the coil in the engine is not damaged. Check the AC output with a 12v bulb as well as with a voltmeter.

I would have thought that a 20 Ah battery would have taken around 2 amps without problem and the output from a 3W solar panel is so small that it really does not even need a controller. But I just wonder if that could actually be the cause of the problem. What happens if the volts at the battery/ engine output rises way above the output volts of the panel cotroller, especially if it is a shunt regulator.

One possible cause of the problem is a faulty or incorrectly connected rectifier but if the 5amp fuse is between rectifier and battery that should have blown before any damage was done.

If the Autohelm had developed a fault that could have shorted out the battery but hopefully you have a fuse in that circuit that would have prevented any damage. It would not explain the melted insulation on the rectifier earth connection.

If your problem had occured as soon as you switched on I would have asked if you might have connected the battery polarity wrongly. If you connect a battery the wrong way round to a bridge rectifier you will instantly fry the rectifier and maybe also damage the wiring. Possible ??? A fuse may not save the rectifier but it should save the wiring.

Based on my own experience if at any time the Autohelm was in use powered by the DC output from the engine but with the battery not connected you will could well have blown the voltage control circuit in the Autohelm.

Sorry for rather disjointed post ... thinking out loud really.

 

[GART]

Wow Vic
Thanks
The manual quotes 70w output but does not mention Regulated, but Volts & Amps increase with revs.
The solar controller was put in to regulate the outboard as well, but I found it stopped it charging completely, so I bypass it from the outboard.
I don’t think the rectifier can be connected up incorrectly except the AC wires but I assume as both same colour it did not matter. The positive has an in line fuse, and the negative bolts to the engine block. As does the negative from the battery.
I cannot put the battery the wrong way round, the wires would not reach.
Auto helm is fused, but when I bought it, it did not work, by swapping the wires over in the plug it worked. I assumed previous owner had wired up differently to my socket.

 

[Lakesailor]

Rectifiers are buggers.
Any unintentional short on whilst fiddling with the electrics will do for them. Just a spanner touching a live terminal and spolt! done for.

 

[mtb]

if the regulator / rectifier has blown the higher the revs the higher the voltage hence cooking your battery, but you have worked that out for your self ?

cheers
Mick

 

[VicS]

[ QUOTE ]
Whow Vic

[/ QUOTE ] I dont know about that. I thought it was rather a pathetic reply

However to work through your later post.

70 watts is a pretty good output from a small outboard. That's potentially 6amps which might be too much for a 20Ah battery. What is the spec for the battery, does it give a charging rate? It is more typical of the rate for a 70 Ah battery. Ok as the battery charges the current will fall but with an AC output rising to 18 volts it is still going to a touch on the high side, maybe, although I did say that the 1.5 to 2.5 amps you observed would be OK. I am having second thoughts now! The smallish volume of electrolyte in an AGM battery does mean you have to be a bit carefull to avoid overcharging.

You are quite right about the volts rising with revs that is what you would expect from a simple system with no regualtor. Just elementary Physics!

I think I would be tempted to look for a regulator that will control the output from the engine, but probably not worry about the output from the solar panel. I have a 5 watt panel permanently connected to my battery suplementing a meagre 5amps maximum from the outboard but I do have a 60Ah conventional wet leisure battery.

You are right about the AC input to the rectifier being reversible and if you cannot physically connect the DC side wrongly thats not the cause of any problem. I mentioned the fact that getting the battery reversed is instant death to the rectifier because many people do not realise it. I have even had people tell me I am wrong but once it is explained they meekly say "Oh yes". Anyway I am always suspicious when something like this happens after curing some totally unrelated fault.

Your logic about the wiring of the Autohelm is reasonable. I have a A/H 1000 (pre digital) and although i have always taken care that it is wired correctly what others have said on here in the past seems to imply that they are not damaged by being incorrectly connected.

Still absolutely no closer to understanding what went wrong on you I'm afraid. I just cannot see where a sufficiently large current to melt the insuation on the earth connection of the rectifier could have come from at least with a correctly connected batterey and a 5 amp fuse in the circuit. About all you can do is to check the coil, it should light a car headlamp bulb, replace the rectifier and progressively check and reconnect every thing else one thing at a time double checking that everything is correctly connected.