Sinbad Posted January 30, 2009 Report Posted January 30, 2009 Just had to get out for a quick blast today to check everything was still OK with the charging / battery. two weeks ago the engineer has checked over the charging and connections, and condemned the brand new battery purchased from BHG! So with the remaining old batttery in place, took the boat out of the marina and firststop round to the quay to review millionaires row. Even in these austere times, I counted at least 10 very large super yachts in the sunseeker dock, in various stages of completion!! Then it was such a snotty chop in the harbour, a good force 4-5 SE breeze and cold, I went on a cooks tour, down Wills cut towards brownsea, round the back to stone island, then followed south deep round the back of furzey and green islands. Nice flat water round here, and a chance to open the throttle a bit more... In the marina, with the engine idling - seemed to produce 13.2Volts... Round to the quay, voltage at times got up to 13.6, then after a bit of low speed manoevering (in gear, and out of gear) next to sunseekers, I noticed it seemed get stuck arround 12.6V irrespective of throttle opening. Quick switch off of Engine, then re-start, and engine starts to show over 13V again, and even got up to 14.8V at times.... So, was the low volts due to a partly discharged battery, and as the charge built back up on the battery, the voltage started to rise ? The Engine seemed to need a bit of time at wider and wider throttle openings before the charging seemed to show. Cant explain why the voltage suddenly showed a step change upwards, after a quick engine re-start, unless there's a fault still somewhere. Would this be the rectifier/charger circuits not switching over to charging properly ? Does putting the engine in gear have something to do with it, as there is an interlock with the engine start ?? Anyway, despite all the guage watching, to have the harbour to myself and a chance to play in the waves for a while did me some good and blew a few cobwebs away at the same time. Just hoping next week the winds drop light, and might be able to get a few late whiting before we call the end to the season..... Paul Quote
charlieannear Posted January 30, 2009 Report Posted January 30, 2009 I'm no expert, but I think you should be seeing something like 14.2v at all times, with very little variation. Has your outboard got an actual alternator, or just a rectifier? I'm sure someone like Charlie or Bob will know more, but I think (sorry) something's still not right there. Quote
Paul D Posted January 30, 2009 Report Posted January 30, 2009 You should be seeing around 14.4 volts to charge the battery. Lower than this and you will not be charging the battery or not charging the battery sufficiently ( 13.8 V will trickle charge a lead acid battery ) See below for some useful values : Battery Charging Voltages Would also be useful if you had an ammeter to see what sort of charging current ( not much I suspect ). My guess as to the problem ? - Regulator ? Quote
Sinbad Posted January 30, 2009 Author Report Posted January 30, 2009 (edited) Hmm - I was suspecting something. I've been running a test meter across the battery terminals - so it might not show the rectifier output exactly. Does your O/B give out 14V+ when Idling ? Any thoughts about why it seemed to switch on when I restarted the engine ? Paul Just looked at the 'workshop' manual.. and there's no alternator - and the rectifier voltage is suposed to be 14v@1500rpm and 18V at 3500rpm, so it does vary, but what this equates to at the battery, and how it stops it overcharging the battery I dont know... more investigation required Edited January 30, 2009 by Sinbad Quote
Bob F Posted January 31, 2009 Report Posted January 31, 2009 Certainly got some weird voltage readings going on. The 12.6V reading whilst the engine is running does not indicate a bad battery, but it's not a normal reading either (when the engine is running). If there was a bad cell in the battery the voltage would actually be very high (above 14.4v depending on the rating of your charging circuit (i.e. the charging circuit would produce its maximum regulated value usually between 14.5 and 14.9V). A reading a 12.6v is exactly what you would get from a 100% fully charged battery when the engine is off. But you shouldn't see 12.6V when the engine is running. It would normally be higher than 13.4v. A reading of 14.4v or slightly higher just after turning on the engine is normal. The circuit is sensing that the battery has been drawing a lot of current to start the engine and so the alternator produces its maximum output to recharge the battery. On a pleasure fishing boat where we typically do short engine runs of less than a hour, our batteries never get fully recharged (because a battery needs many hours of continuous charge to charge it properly). So, on our fishing boats it's typical to see the voltage readings always being over 13.8v (i.e. the alternator is sending charge to the battery because it is not fully charged yet, or there are other circuits like lights and electronic equipment that are drawing current from the alternator). If you say that the battery, connections and cables have been verfied, then I think you are left with two things to check. 1 - the regulator or 2 - check if there are any fuses in the charging circuit or around the engine and make sure they have not blown. How where the connections checked? Was it just a visual check and a tightning with a spanner? Or did they perform a voltage drop test across all the cables? This is really the only 100% way of ensuring that your cables and connections are fully operational. But I'm not an expert, either. BF Quote
Sinbad Posted February 1, 2009 Author Report Posted February 1, 2009 Hi Bob, Thanks for your input, looks like Ive got a few more things to check.... its getting to that time of year, when there'll be plenty of time to go through the lot - more carefully. Pity its been so blooming cold lately - Ive already spent one day on my knees in my float suit, head in the bilges... More coming up I suppose... Paul Quote
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