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stewal
stewal

Posted: Wed Apr 27, 2011 9:59am

Post Subject: battery montitor

Hi Tony, I have just fitted a battery monitor which required the shunt to be in the negative lead. As I have twin alternators and the negative termindals for both starter and domestic banks are common it is now reading the current produced by both alternators. If I directly connect the negative from the engine to the starter battery the monitor no longer reads current into the domestics. Whilst its not creating any particular problem is there an easy way of isolating the monitoring of the alternators when they share a common negative connection to the battery bank? I understand this would be possible for the positive lead but the monitor must be on the negative side apparently. Thanks.

Tony-B
Tony-B

Posted: Wed Apr 27, 2011 4:42pm

Post Subject: battery montitor

Good practise dictates the shunt should be in the negative side because it prevents a short to hull on the two shunt to meter leads causing afire. Other than that it is down to the design of the actual unit. Unless the shunt & meter are designed to handle high currents like those imposed by a large inverter or the starter motor you should also avoid these being passed through the shunt. As long as no large inverter is involved I think fitting the shunt in the negative link between the starter and domestic bank will do what you want as long as the main earth to the engine is run from the starter motor negative and not the domestic negative terminal. Otherwise I will need an accurate wiring diagram for your boat to see if I can work out how to wire it. The best plan would be to make the supplier's technical department earn their keep and advise you. Just to make your day I hope that you are aware that such devices have a regular and nasty habit of telling lies. After a very short time they lie about the degree of charge in the battery but not the amount of discharge. The reason is that the extra amount of current required to get batteries back to the same degree of charge as they were in before the last discharge varies according to temperature, battery condition and battery construction. If you intend to use this to tell you about the state of battery charge I would suggest that log onto the Smartguage website and settle down for a period of technical study. Tony Brooks

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