New AGM batteries have caused low charge alarm to sound at tickover

O

OMG626

New Member
Joined
7 Jun 2021
Messages
5
Visit site
Hi folks,
I have upgraded my house batteries (2x 110Ah) from cheap old lead acid car batteries to proper marine grade deep cycle AGMs.
Great, except that has now caused the low charge warning alarm to sound on tickover, which is incredibly annoying for everyone on board as it is LOUD!
Presumably the lower internal resistance of the AGMs means the alternator is now not generating enough to lift the voltage at low revs??

Question is, am I going to have to now invest in an alternator upgrade as well, or is there something else I can do to adjust the alarm level?

Afraid I don't know what alternator I have, but the engine is a 34 year old Yanmar 3HM35.
I replaced the drive belt last year and I don't believe it is slipping, but I will try tightening that first (haven't had a chance yet).

thanks
Tim
 
Did you ensure the new batteries were fully charged before fitting them?

As an ex pro Car Mechanic and Motorcycle Shop and Garage owner I know how batteries lose charge when stored.

We had a weekly regime of checking/charging if required.

Not all outlets do the same.
 
Strangely, I had the same thing happen when I installed new agms. I could get the alarm to shut off if I gave the engine some beans for 5-10 seconds. This persisted for about a week or so then it stopped doing it for no apparent reason. Hasn't done it since either 🤔.
 
Are you talking about the exciter based alarm ?

This sounds when exciter voltage is still coming basically from battery and not countered by Alternator .... as you increase engine revs - the Alternator output rises and basically equals / exceeds exciter voltage .... alarm stops.

I would suggest that your AGM's may be puttying out slightly higher than your old batts ... so Alternator is having to be at a slightly higher rate to counter.
I say this because I know when my on-board batts are really highly charged as I need slightly higher rpm on engine to stop the alarm ....
 
robmcg said:
Strangely, I had the same thing happen when I installed new agms. I could get the alarm to shut off if I gave the engine some beans for 5-10 seconds. This persisted for about a week or so then it stopped doing it for no apparent reason. Hasn't done it since either 🤔.
Click to expand...
My AGMs (Rolls 4x100Ah) have done that when starting from time to time since fitting in 2010. I never thought more about it as after a blip of high revs the alarm stops and we drop back to tickover.
 
Refueler said:
Are you talking about the exciter based alarm ?

This sounds when exciter voltage is still coming basically from battery and not countered by Alternator .... as you increase engine revs - the Alternator output rises and basically equals / exceeds exciter voltage .... alarm stops.

I would suggest that your AGM's may be puttying out slightly higher than your old batts ... so Alternator is having to be at a slightly higher rate to counter.
I say this because I know when my on-board batts are really highly charged as I need slightly higher rpm on engine to stop the alarm ....
Click to expand...
Yes, that's the one. It does stop as soon as any revs put on the engine, but it will come back whenever I go into neutral, even if I've been motoring for an hour or more and batteries are full.

I guess the simplest fix is to increase engine tickover speed until it stops, might mean a bit more wear on the gearbox going in and out of forward/reverse...?
 
OMG626 said:
Yes, that's the one. It does stop as soon as any revs put on the engine, but it will come back whenever I go into neutral, even if I've been motoring for an hour or more and batteries are full.

I guess the simplest fix is to increase engine tickover speed until it stops, might mean a bit more wear on the gearbox going in and out of forward/reverse...?
Click to expand...

That should not happen surely - somethings possibly not right.

Once the alternator is supplying charge - the exciter lead that triggers the alarm should be at zero potential. Sounds like the alternator is failing at low revs... dropping below the level needed to match the excitation.

Its a b it like the old dynamo / weak alternator days of cars .... I'm old enough to have sat and seen the Red Ignition light flickering when engine idling ... its the same thing. Insufficient output matching the exciter ...

I have a bog standard car size alternator on my Perkins 4-107 ... nothing special at all .. probably in the 50A range ... My BEEP will sound until about 1000 - 1100rpm then is matched ... and stops. Of course I blip throttle to maybe 1200 - 1400rpm to clear starting crud anyway ...
But once alarm stops with that blip - I can close throttle down to idle at about 600 - 650rpm and still no alarm.

I know my alternator is well past its sell by date ... because the decay of that exciter field is rapid after stopping engine. In theory I should be able to restart the engine after a few minutes and no alarm ... but even if I immediately restart - it sounds ... fields decayed.
 
Do you have solar panels as well charging the batteries? If the solar controller voltage is higher than the alternator on tick over, the alarm will sound and the light may also flicker on. This is because the regulator in the alternator will shut it down.
 
Boater Sam said:
Do you have solar panels as well charging the batteries? If the solar controller voltage is higher than the alternator on tick over, the alarm will sound and the light may also flicker on. This is because the regulator in the alternator will shut it down.
Click to expand...
That makes no sense. I have solar on my engine start batteries but that doesn't happen. The alarm is sounding because the voltage is low not because it is high
 
OMG626 said:
Hi folks,
I have upgraded my house batteries (2x 110Ah) from cheap old lead acid car batteries to proper marine grade deep cycle AGMs.
Great, except that has now caused the low charge warning alarm to sound on tickover, which is incredibly annoying for everyone on board as it is LOUD!
Presumably the lower internal resistance of the AGMs means the alternator is now not generating enough to lift the voltage at low revs??

Question is, am I going to have to now invest in an alternator upgrade as well, or is there something else I can do to adjust the alarm level?

Afraid I don't know what alternator I have, but the engine is a 34 year old Yanmar 3HM35.
I replaced the drive belt last year and I don't believe it is slipping, but I will try tightening that first (haven't had a chance yet).

thanks
Tim
Click to expand...
You changed your batteries, what connections did you undo, redo, or otherwise disturb? Have a good check of all the associated connections first before getting too technical.
 
Gumpy said:
On a 12v system fitting a 47ohm 10watt resistor in parallel with the ign light usually means you will never have to blip the throttle again to stop the alarm sounding when you first start the engine.
Click to expand...

Personally I like to have that alarm sounding on start up ..... having had alternator failure in the past - its a feature that gives me actual indication that alternator has built its 'field' and is now charging when the alarm and light go out.

Yes its an annoying beep - but that's what an alarm should be.
 
Refueler said:
Personally I like to have that alarm sounding on start up ..... having had alternator failure in the past - its a feature that gives me actual indication that alternator has built its 'field' and is now charging when the alarm and light go out.

Yes its an annoying beep - but that's what an alarm should be.
Click to expand...
Sure, if it was just on start-up that would be fine, but it's ALL the time I go into neutral/tickover, which I am just not prepared to just put up with.

I did have to modify the cabling to the batteries and put in a new victron shunt, but fairly sure all those connections are 10X better than they were before.

Later this week I will experiment with tightening the alternator belt and seeing how many extra tickover revs are required to silence the alarm, hopefully it's just a small increase and then problem solved.
Thanks all
 
OMG626 said:
Sure, if it was just on start-up that would be fine, but it's ALL the time I go into neutral/tickover, which I am just not prepared to just put up with.

I did have to modify the cabling to the batteries and put in a new victron shunt, but fairly sure all those connections are 10X better than they were before.

Later this week I will experiment with tightening the alternator belt and seeing how many extra tickover revs are required to silence the alarm, hopefully it's just a small increase and then problem solved.
Thanks all
Click to expand...
Just a thought, and not knowing your wiring arrangement. I know that the shunt will be on the -ve side of the battery. Have you considered that there maybe a volt drop caused by the shunt which is causing the excitation problem with the alternator at low RPM? perhaps if you tried a slightly higher wattage lamp in the circuit the resultant reduction in resistance may solve the problem?? If it does it would be interesting to know if the insertion of the shunt was the cause and you were not just treating the symptom and not the fault.
I am flying a bit of a kite on this one, as I say not knowing the actual circuit. Just that you have a new problem and a new bit of kit so does 1+1 = 2?
 
You must log in or register to reply here.

Other threads that may be of interest

N
Volvo Penta Alarm Module/Alternator Issues
Replies
1
Views
226
superheat6k
superheat6k
B
How does a tacho get RPM and engine-hours data, and how to fix faulty readings?
Replies
17
Views
604
Centurion11
C

Share this page

Top