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foremarque
foremarque

Posted: Wed Mar 30, 2011 5:38pm

Post Subject: Tachometer not working

OOps! I switched off the ignition on my Teddesley boat whilst the engine was running,instead of using the engine stop, and now the Tachometer refuses to work. I also notice that if I have both the engine and domestic batteries connected,the voltmeter shows 12v. but if I disconnect the engine battery it goes up to just above 14v. There is supposed to be a split charging relay, and there is a Sterling advanced regulator fitted. Have I blown the relay as well? I took the alternator to a specialist and they have confirmed that it is charging ok and that the Tachometer output is also alright. Nevertheless I took the opportunity to buy an exchange unit with a higher rated capacity of 70 amps. I have 5 110amp batteries and one starter 95 amp battery fitted, and I think they may be ending their life. Do I need to upgrade the relay to cope with the higher alternator output?

Tony-B
Tony-B

Posted: Wed Mar 30, 2011 7:17pm

Post Subject: Tachometer not working

First of all as long as the system is correctly wired there is NO WAY in which simply turning the ignition switch off can damage an alternator. The alternator's regulator does it at over 100 times a second.Now, the voltmeter should not be connected to both batteries. You should have two voltmeters, a change over switch or just possibly a diode in the feed from each battery to prevent one battery discharging into the other. However in the latter case the voltmeter would always read low by about half a volt. Perhaps the voltmeter is only monitoring one battery but if so I do not see how the voltage could drop so much when both batteries are connected. In fact the voltmeter should never be able to get to 14 volts with a stationary engien unless you have a mains charger in use. I just hope that you have not disconnected the engien battery with the engien running. If you have you may well now have wrecked the alternator because it is the removal of the load that causes damage. I need a wiring digram for your boat's charging system before I can even start to make some sense out of your email - it makes no sense with the information you provide. When you turn the ignition on does the red warning lamp come on. If not you need to find out why because that has a crucial role in getting the alternator charging. There is a chance the you may have welded the split charge relay contact together if it tried to break under load when you turned the switch off, but this implies the relay is ignition switch controlled. It may not even be a relay, it could be an electronic charge splitter. The 12 volts could be true if the starting battery was very discharged and the relay contacts were stuck shut, but I would need to be on the boat to check. In fact I think it would be easier to pay someone to test and sort this out than try to DIY with long distance help. I have no idea if you need to upgrade the relay unless you give me the data sheet for it. If its a Durite or Lucas 40 amp unit then yes, you do need to upgrade it. If its a black box 120 to 160 amp unit then you may be well advised to upgrade it. If its an Albright unit it should be fine. I am sorry that I can not be much help but I think this one needs instrument testing to find out what is going on. It may be helpful to you if you email me (tony@tb-training.co.uk) and tell me the area the boat is in. I expect to be visiting three boating areas over the next week and may be able to find time to have quick look for you. Tony Brooks

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