Suspicious electrics

[Morpheous]

I suspect that my port alternator isn't charging - the volt meter is reporting 12 volts which I think is a bit low. Stbd reports about 13. I also notice that when I plug the shore power back in I get a big current draw from the mains battery charger for quite a while. I have had lots of unreliable guages - temp in particular over reads (confirmed by infra red), that's 20 year old electrics I spose. I have been working may round the varous senders etc cleaning connections and I now have sensible readings mostly.

How can I easily check the alternators - I have read you have to check the voltage across the batteries - but they are not that easy to get at and I don't know which alternator changes which batteries.

Thanks

 

[mont]

hi,
Where are you getting the alternator voltage readings from - guages ??
Do the readings increase with engine revs ??
Have you got old style split charging diodes ??, whereby the different alternators initially charge different banks of batteries first then 'switch over' to the other bank or biggest draw which is usually the house/ aux system. They will take possibly 1v off the alternators output.
The battery charger will probably not be passing through the diodes and so will probably top up the shortfall at the batteries - hence the surge of charging.

FWIW - I have noticed with my charger (modern 2 yo unit) that when you first plug in shorepower it goes into a boost charge mode (13.5 / 14v at guages) then settles back into a trickle / demand top up mode 12.5v to 13.5v at guages.

 

[Stoaty]

I also notice that when I plug the shore power back in I get a big current draw from the mains battery charger for quite a while.

Sounds to me more like bad batteries than an alternator problem. You say they are difficult to get to. How do you top them up? when did you last do it? How old are they? If you have a duff cell or cells then the alternator may well not charge above 12v. The charger working hard for a long time also sounds like a battery that will not take a charge. You need to measure the voltage with a digital meter after a 12hr rest. It should be 12.4 or more if it's ok if it's under 12 it's probably dead.

 

[Nigelhg]

What is your charging setup- do you have two seperate engine batterys and then a domestic set? Do the engines even charge the domestic batteries - sunseeker wired a lot of boats (including mine) with only shorepower charging the domestic batteries. It could be that whatever battery that your port engine is charging is very low or even may have a bad cell dragging the voltage down. You could try to confirm this using a multimeter on the battery when charging.

If you have the orginal boat manual there may a wiring diagram for your boat in it which will show your charging set up.

If you need to test your alternator you might be better to remove it and take it to a specialist who can test it under load.

Hope this helps - Nigel

 

[spannerman]

First test your alternators output with a voltmeter on the back of the unit usually a large red cable, this should be between 13,8 and 14,2 at high idle 1500rpm. If they are good then work towards the batteries checking the voltage at switches, split charge relays etc, you shouldn't lose more than 1.5 v otherwise you have to look for bad connections, dodgy wiring etc. If the batteries are getting at least 13,5 v then thats fine and your low readings are a fault between the engine, harness, ignition switch, voltmeter. The quickest way is to check the voltage at the ign switch if its low then work back to the motor, if its OK work forwards to the instruments, if the voltage is good there then its a bad earth.

 

[epervier]

I suspect that my port alternator isn't charging - the volt meter is reporting 12 volts which I think is a bit low. Stbd reports about 13. I also notice that when I plug the shore power back in I get a big current draw from the mains battery charger for quite a while. I have had lots of unreliable guages - temp in particular over reads (confirmed by infra red), that's 20 year old electrics I spose. I have been working may round the varous senders etc cleaning connections and I now have sensible readings mostly.

How can I easily check the alternators - I have read you have to check the voltage across the batteries - but they are not that easy to get at and I don't know which alternator changes which batteries.

Thanks

It's probably no help to you whatsoever, but mine is exactly the same, stb engine running 13+v port engine just on 12v, a few months ago it never reached 12v, removed it sent for repair had a diode pack go out, came back like new but only with 12v, but, the port alternator charges, the port start battery, and both domestics,

so it is working hard to charge all three, also all my batteries I replaced this season, with 135ah starts, and 135ah deep cycle domestics, plus I'm on a swing mooring, so no shore power to boost heavy usage,but so far no problems with flat batteries.

 

[Morpheous]

Wow a barage of responses here thanks very much. I'll try to add some more info - firstly this is my first mobo and not really sure of alot of it hence the post! Sadly don't have any of the original manuals, I do have some handwriten diagrams done I suspect when the battery charger was upgraded.

I can top up the batteries and they do need doing, I just have to take out the back seats to do it and this can't be done when swmbo is on board cos the moaning is unbearable.

Stb guage does increase a little with engine revs, port hardly moves at all. I think the batteries are ok - I haven't had a problem starting and the domestics seem ok - family keeps forgetting switch off lights etc.

I have no idea what sort of diodes I have or how the charging is arranged - this has been a learning year and the learning continues!!! There is a something with a black heatsink on the bulkhead but I haven't worked out what it is yet!

So basically I can put a voltmeter across the main terminals on the alt and should get a reading from that? That is what I hoped for.

Do I gather then that the batteries should be tested with everything off - prefereably rested then and I should get 12.4? Interestingly the meter on the fuse box in the cabin seems to show a rosier picture adding to my suspicion of the guages. I do also have suspect I have losts of bad connections in the bay. I have had water splashed around (leak from strainer on to drive belts) and lots of green aerosol spray over everything.

 

[Morpheous]

It's probably no help to you whatsoever, but mine is exactly the same, stb engine running 13+v port engine just on 12v, a few months ago it never reached 12v, removed it sent for repair had a diode pack go out, came back like new but only with 12v, but, the port alternator charges, the port start battery, and both domestics,

so it is working hard to charge all three, also all my batteries I replaced this season, with 135ah starts, and 135ah deep cycle domestics, plus I'm on a swing mooring, so no shore power to boost heavy usage,but so far no problems with flat batteries.

Maybe I'm worrying over nothing then. I've got 4 in mine, any idea which ones would be which? Sorry newbie can't tell the difference between starts and domestics.

 

[halcyon]

Maybe I'm worrying over nothing then. I've got 4 in mine, any idea which ones would be which? Sorry newbie can't tell the difference between starts and domestics.

Turn on batteries, swotch on ingnition so you have a voltage on voltmeters, turn on cabin lights.

Turn off one battery switch, do the lights go out ? which voltmeter does not read a voltage?

If the lights go out, then the engine with zero volts is supplying engine and domestic power.

If the lights stay on, then the voltmeter without a reading is for engine only.

Do check with other isolator to check lights go out.

You will also need to check that one engine will not start each time, both engine could be on one battery bank.

Brian

 

[epervier]

Maybe I'm worrying over nothing then. I've got 4 in mine, any idea which ones would be which? Sorry newbie can't tell the difference between starts and domestics.

PM me your email, I'll send you scanned copies of the boats wiring diagrams and layout, if you wish.

 

[Morpheous]

Turn on batteries, swotch on ingnition so you have a voltage on voltmeters, turn on cabin lights.

Turn off one battery switch, do the lights go out ? which voltmeter does not read a voltage?

If the lights go out, then the engine with zero volts is supplying engine and domestic power.

If the lights stay on, then the voltmeter without a reading is for engine only.

Do check with other isolator to check lights go out.

You will also need to check that one engine will not start each time, both engine could be on one battery bank.

Brian

Ah that sounds very logical, I'm pretty sure the engines start only when the corresponding isolator switch is on. Thanks

 

[epervier]

email sent

 

[Morpheous]

Brilliant, thanks for that very helpful

 

[Morpheous]

Spot the component???

Checked the alternator output, it's kicking out between 13.5 and 14v so I reckon it's ok. Batteries alll topped up belts tightened, fluids checked etc. Productive weekend.

However I did find this (pic attached hopefully) It has 2 sockets, and floating next to it there are wires with plugs that will fit in the sockets. Any idea what this is? I don't want to randomly reconnect them because I think everything is working so my guess is it is something that has been replaced or superceeeded???