Yanmar charging light faintly glowing, 13.8V across battery

[Playtime]

My first thought actually but then I realised he showed a 10 amp discharge with lots of stuff switched on and a 3.8 amp discharge with less switched on.

You're right . . . . . again.

If it's not a fault in the BM1 wiring, though, I am struggling to understand how the alternator is shoving out 14.3V but the battery is showing a discharge.

I will await the final outcome with interest.

 

[GlennG]

When the pic was taken, the batteries had been disconnected for a couple of weeks but had not been used. Prior to that they were fully charged, having been connected to a Stirling intelligent charger for a couple of weeks.

Normally I don't leave her connected to shore power, but this time of year I do like to run a dehumidifier.

The discharge being shown is all the internal lights on with, I think, the instruments. When I turned on the running lights and as much as I could, it drew (or indicated that it drew) just over 10A.

I would have expected the alternator to take up the slack.

Annoyingly I didn't have enough time to 'play' with the newly fitted monitor. Worse still, I can't even make it up to the boat this weekend:-(

 

[VicS]

I would have expected the alternator to take up the slack.

The fact that the voltage indcated is 14.3 volts shows that the alternator has "taken up the slack" and is maintaining its normal output voltage at which it will be charging the battery.
If it had not the volts would have fallen down below the normal resting volts of around 12.8
Your charging current must be by passing the BM1 shunt. Only the discharge current is passing through the shunt and being measured.

You need to sort out the wiring of the shunt and the battery.

 

[GlennG]

Thanks for that - a really good point. I'll chase down the wiring as soon as I get back to her, unfortunately not until next weekend. The first test is to simply compare the voltage+current with the engine running and not.

Had this weekend off - went down to Lymington to a Contessa 32 class association event. Various really interesting talks then a trip to Jeremy Rodgers building to see the two new Contessa 32's in production. Really odd to see light showing through a hull which is in the early stages of construction. Nice to see that people are still buying them in their 40th year

 

[prv]

we're talking about a Yanmar 2GM20 with conventional alternator and starter, as far as I know, which have an engine connected earth or negative return for both components.

Dredged up from a while back in the thread, I know

Can anyone else confirm that the alternator return on the 2GM20 is through its case? I'm replacing all the "heavy" cables next weekend, and this will make a difference to me. The workshop manual doesn't specifically say, but it does show an earth terminal, from which I'd assumed it was isolated return (albeit the standard loom then connects it to the block further down the line).

Cheers,

Pete

 

[steve28]

It is an insulated negative but as you say its strapped to the block further down the line.



Steve

 

[GlennG]

Update - all OK... errm, what was the problem?

I had mis-wired the battery monitor, connecting the two batteries together which effectively allowed the alternator to by-pass the shunt. I re-wired it today (RTFM) and, yippee, it's working well.

The boat's been plugged into the mains over the last few weeks, not least to run the de-humidifier. The batteries have been on charge during this time.

I turned off the shore-powered charger before starting the following.

I turned on everything I could: cabin lights, nav lights, nav gear, radio, heater blower, fridge and saw there was a voltage of around 12.2V with a current drain of 15A (photo A). After about 45 mins of this (I'd found some other things to turn on) it was reading 11.7V / 20A (photo B).

I started the engine with the 2-way switch on to the starter battery. Ran it up to 2000RPM. Switched the battery switch through both to the house battery and there was a marked change in engine note as it took up the load. The battery monitor showed 13.3V and a charge of 22A (photo C). To me this means that the alternator's pushing 42A, e.g. 20 + 22A. After about 30 mins this slowly changed to 14.1V / 9.8A.

So, all looks well - I am rather chuffed with this tool.

Now, what about that charging light? It's still faintly glowing!

I guess it's one of those things that until you have the right measurement tools, you just don't know what's going on. On a positive note I've learned loads about the charging circuit and spent some quality time on the boat


To do...
I'm fairly sure that I'm going to fit a diode isolator block for the charging circuit, to isolate the batteries. This way it's idiot proof; whenever the engine's on, it'll charge both batteries. I will leave the big battery switch alone, but leave it switched to the starter battery - the diode block will charge the house battery. As the alternator's only 55A, I'll only need a cheaper diode block.

I'm going to research one of those 'advanced alternator regulator' thingies, such as the Stirling unit. Don't need to spend mega bucks on the tap-dancing digital one with optional control panel; just one that'll properly regulate the voltages and not cook the batteries.

Thanks for everyone's help.

 

[VicS]

Glad to hear you have the battery monitor working well. RTFM as you say. (You've done the setting up and zeroing in "Engineering mode" ?)

Still a puzzle about that warning light but the alternator seems to be generating OK!. That seems to rule out the theory that one of the field diodes has failed. Back to a poor connection somewhere ?? but there aren't many places it could be and give that symptom.

If you fit a diode split charging system you really need to modify the alternator to "battery sensing", if it is not already, in order to compensate for the volts drop across the diodes.

A VSR system is an alternative which does not suffer from the volts drop of the diodes.. To which end you can get a VSR isolator switch cluster which incorporates the VSR, the battery isolators and an emergency linking switch (A few more ££ though)

There are electronic alternatives eg Driftgate's X-split.
Someone will be along shortly I am sure to recommend a Cyrix device

One step up on that are Sterlings AB chargers. These are add-on electronic devices that require no alternator modification but simultaneously give enhanced charging of the domestic battery and standard charging of the starter battery. So offer the benefits of an advanced regulator and replace the split charging system at the same time. ( see the recent topic http://www.ybw.com/forums/showthread.php?t=266704 where there is a good wiring diagram in post #23)

Sterlings Advanced alternator regulators require a small modification to the alternator and will still require a diode or VSR system to charge two batteries.

I you have a 1, 2, both switch at present now is the time to ditch it!

 

[Playtime]

I turned on everything I could: cabin lights, nav lights, nav gear, radio, heater blower, fridge and saw there was a voltage of around 12.2V with a current drain of 15A (photo A). After about 45 mins of this (I'd found some other things to turn on) it was reading 11.7V / 20A (photo B).

Good to hear that the alternator is working well and that the BM1 has proved effective.

Looking at the above figures for discharge I would be a bit concerned about the state of your batteries.

If they have been on mains charge for a few weeks they should have been fully charged before the start of this test. It is therefore a bit surprising that the volts dropped to 11.7 after a discharge of less than 15Ah.

What size is the battery (bank?) and how old?

Also, have you checked the water level lately? After a few weeks on mains charge it could well be down a bit.

 

[GlennG]

Good point re batteries.

Not really sure what the battery size is but I think they're a pair of 75 or 85Ah Delphi Freedom sealed lead/calcium batteries. They're well held and not easy to get to their sides without undoing everything. But they are old; I've had her for 6 years.

When I was running the discharge test - about 45-60 mins on 15A+, I went to start the engine and it barely turned over. The switch was on the house battery, so I switched over to the starter battery and it started immediately.

Maybe the batteries are on their way out.

A picture of the batteries is attached. I've not yet finished the wiring - want to look at adding a (fused) positive bus bar; there's a -ve bus bar to the left of the picture (out of shot). I also will be replacing some of the wiring.

Any ideas what size the batteries are?

The thing I'm most pleased about is when running the engine and switching the batteries from the starter battery to both then house, the tone of the engine markedly changed. With hindsight (!) I should have done this test before to check out the alternator: discharge the battery for a while then flick the switch to see if the engine load increased.

Anyway, I'm pleased with the meter - a worthy addition to the boat.

 

[VicS]

Any ideas what size the batteries are?

Difficult to tell from the photos esp with nothing much to judge the scale against. I'd guess not as big as 110 Ah ... nearer the size you think.

Measure them and compare with the measurements given on one of the battery suppliers websites. I wont necessarily identify them exactly but it should give you some sort of idea.

 

[mjf107]

Good point re batteries.

Not really sure what the battery size is but I think they're a pair of 75 or 85Ah Delphi Freedom sealed lead/calcium batteries. They're well held and not easy to get to their sides without undoing everything. But they are old; I've had her for 6 years.

When I was running the discharge test - about 45-60 mins on 15A+, I went to start the engine and it barely turned over. The switch was on the house battery, so I switched over to the starter battery and it started immediately.

Maybe the batteries are on their way out.

A picture of the batteries is attached. I've not yet finished the wiring - want to look at adding a (fused) positive bus bar; there's a -ve bus bar to the left of the picture (out of shot). I also will be replacing some of the wiring.

Any ideas what size the batteries are?

The thing I'm most pleased about is when running the engine and switching the batteries from the starter battery to both then house, the tone of the engine markedly changed. With hindsight (!) I should have done this test before to check out the alternator: discharge the battery for a while then flick the switch to see if the engine load increased.

Anyway, I'm pleased with the meter - a worthy addition to the boat.

Interesting that the batteries may be failing, in my researches I've come across several posts claiming poor batteries have a bearing on "glowing" charge lights, but unfortunately no technical explanation of why this should be. Maybe its the failing ability of the battery to smooth the ripple from the alternator diodes???

 

[halcyon]

Interesting that the batteries may be failing, in my researches I've come across several posts claiming poor batteries have a bearing on "glowing" charge lights, but unfortunately no technical explanation of why this should be. Maybe its the failing ability of the battery to smooth the ripple from the alternator diodes???

You get it if a field diode has failed, one pluse is missing, so the ign light earths via rotor and regulator to earth. This keeps the output going for that plulse, but possibly at lower current level.

Or if you have a earth leakage, the bulb can earth between field diode pulses, giving a dim glow.

It is possible also that the field diode output voltage is higher than the battery voltage, and you are getting a reverse flow. Normally this will not happen as the field diodes are in sync with the main positive diodes. But if the battery is starting to fail it may have a low peak voltage, allowing a charge current from field diodes via bulb.


Brian