Intermittent Aternator Light

[TimFromLI]

Last night I went for a sail, maybe 2 hours, had the fridge on, nav lights for 2 hours and auto pilot for about 30 minutes. When I started the engine, the alternator light came on for about 15 minutes and then shut off. this is the second time in 2 weeks that this happened. 6 trojan t105's installed in spring 2020, Balmar 100amp alternator rebuilt in 2020. Belt and terminals seem fine, I have a 2 week cruise coming up on 8/2. What do you think? Batteries? Any way to test them besides resting voltage?

 

[dlochner]

Odds are there is an issue in the wiring harness. Check for continuity on the leads to make sure the connection is OK.

Do you have a battery monitor to monitor the amps going into the battery? Can you use a clamp on ammeter to read the current when the light is on and off?

 

[Don S/V ILLusion]

My understand is that idiot light indicates voltage. Check schematic to verify. Absent info about measuring your voltage pattern during and after start-up, my wild guess is a regulator issue although any of a number of high resistance connections in the harness can exhibit a similar problem.

 

[rgranger]

Speaking from ignorance and riffing off of @dlochner & @Don S/V ILLusion ... Is your "alternator" light an idiot light that only comes on when the voltage is low?

You described sailing for a while with a bunch of load bearing devices running.... I could not help but wonder if the light came on because you needed to charge and then went off when the voltage reached a set level. If that is what you experienced... I might suspect that you simply ran the voltage down a little.

 

[TimFromLI]

Speaking from ignorance and riffing off of @dlochner & @Don S/V ILLusion ... Is your "alternator" light an idiot light that only comes on when the voltage is low?

You described sailing for a while with a bunch of load bearing devices running.... I could not help but wonder if the light came on because you needed to charge and then went off when the voltage reached a set level. If that is what you experienced... I might suspect that you simply ran the voltage down a little.

I believe it's an idiot light and just senses voltage, so the batteries may be run down. I have 660AH of batteries so they should be able to handle the fridge and 20-30 mins of autopilot. I have to look at the regulator charging profile. I thought it started at 12.8v and steps up. I will test voltage at the battery and compare it to the idiot light voltage. maybe there's a bad connection

 

[dlochner]

I believe it's an idiot light and just senses voltage, so the batteries may be run down. I have 660AH of batteries so they should be able to handle the fridge and 20-30 mins of autopilot. I have to look at the regulator charging profile. I thought it started at 12.8v and steps up. I will test voltage at the battery and compare it to the idiot light voltage. maybe there's a bad connection

Is this on a Yanmar? If so, Yanmar wiring harnesses are notorious for developing faults. The Tach is a frequent issue as is the power to the starter solenoid.

 

[TimFromLI]

no it's a volvo penta tmd22a. I looked at the battery history in the renogy app and the minimum voltage was at 11.4 yesterday and 11.1 the week before - the two times that i noticed the light on. I think its time for new batteries.

 

[Don S/V ILLusion]

no it's a volvo penta tmd22a. I looked at the battery history in the renogy app and the minimum voltage was at 11.4 yesterday and 11.1 the week before - the two times that i noticed the light on. I think its time for new batteries.

Never start with the most expensive fix. You haven’t established the batteries are dead nor why they died if true. The last thing you want to do is buy new batteries annd install them in a faulty system which will kill them too with a bad alternator or charger.

 

[jssailem]

I’m with @Don S/V ILLusion.

you said the alternator was rebuilt. That is one place to start. What is the voltage being sent to the batteries?

Do you have an external regulator or is it on the alternator?

What is the condition of the wire connections?

All of these can crest the issue of weak charging of batteries. Explore the simple and work towards the expensive ( dead batteries).

Had the electrolyte levels been checked in the batteries?

 

[TimFromLI]

I can remove the alternator and have it bench tested but it is more likely than not that the batteries are bad and its not the charging system. I should have measured the voltage before and after running the engine, I'll try it . But - this is the trojans 6th season and they should not go from fully charged to 11V after 90 minutes of running the fridge and 20 minutes of auto pilot even without an alternator. Last season, while cruising, staying on moorings, the batteries never got that low after running the fridge, fans, cpap all night. My Renogy charge controller shows the min and max voltage by day for the past month and each time that it dropped to 11 was when I was out sailing with no motor running. I checked the electrolyte level, they are all fine. Connections look like the day I installed them.

 

[Tally Ho]

I can remove the alternator and have it bench tested but it is more likely than not that the batteries are bad and its not the charging system. I should have measured the voltage before and after running the engine, I'll try it . But - this is the trojans 6th season and they should not go from fully charged to 11V after 90 minutes of running the fridge and 20 minutes of auto pilot even without an alternator. Last season, while cruising, staying on moorings, the batteries never got that low after running the fridge, fans, cpap all night. My Renogy charge controller shows the min and max voltage by day for the past month and each time that it dropped to 11 was when I was out sailing with no motor running. I checked the electrolyte level, they are all fine. Connections look like the day I installed them.

Sounds like my golf cart batteries….leave the dock after being on a charger overnight and they were at 13 volts…2 or 3 hours later, down to 12 volts or less. I did check mine regularly and I am sure they were pretty much shot.
One thing I noticed was that my charger never could get to “100%“ SOC. It always showed it was trying to charge them.

My Duracell 6V GC batteries are on their 5th season.

Greg

 

[TimFromLI]

I am going to replace them with LifPo. For the difference in price it's not worth going with fla again

 

[dLj]

@TimFromLI and @Tally Ho - seems like awfully short time periods for your batteries to go south. How low do you draw your batteries down to while using? What are you doing for equalization cycles as you use your batteries? Details matter.

dj

 

[TimFromLI]

I am on a mooring most of the time. One 165 watt solar panel keeps them topped off I add another 175w when cruising. We spend about two weeks a year on the boat on moorings or anchor. I have over discharged them 2 or 3 times, I went a little too long on the water level 2 or 3 times and I haven't equalized them on a regular basis. I read through Marine Know How site on drop in LifePo. I might be able to get more AH at a cheaper cost than another set of Trojans. My xantrex 458 inverter charger and balmor ars5 regulator are not designed for LifePo. I know they can be tweaked to mimic the charge profile of LifePo but it looks like I can use a Victron DC to DC charger to get around all that. Won't get that all done in a week and I need to research this more, so looks to be a winter project. I will just buy a lot of ice, hope for sun and hope to get the last breaths out of the Trojans on our trip..

 

[Tally Ho]

For me, I am on a dock and the batteries were on a charger pretty much every day. However, my charger is (was) 24 years old and I was not as diligent at watering these batteries in the beginning. I suspect that is the biggest reason for their demise.

I did upgrade the charger for my LifePo4 battery bank.

Greg

 

[Project_Mayhem]

Ive seen a couple of dying car alternators work fine in mid to high RPMs and then the generator light would come on in the lower range. See if it's RPM related. Alternators are actually pretty simple to repair

 

[Don S/V ILLusion]

- this is the trojans 6th season and they should not go from fully charged to 11V after 90 minutes of running the fridge and 20 minutes of auto pilot even without an alternator.

that’s exactly what undercharged batteries will do.

lots of people replace dead or dying batteries without knowing why they are dead or dying. Great revenue source for the industry.

 

[Art12050]

I’ve got fond memories of Port Jeff. We lived in Miller Place for a few years when I was a kid while my father was working on the (then) Lilco Power plant on the harbor. I made my first sailing dinghy out of an old row boat that washed up in a storm. Great summers on the Sound!
Good luck with your charging/battery issues.

 

[TimFromLI]

that’s exactly what undercharged batteries will do.

lots of people replace dead or dying batteries without knowing why they are dead or dying. Great revenue source for the industry.

I'm pretty sure they were fully charged. The boat sat on a mooring and was used briefly for 2 out of 7 days. The min and max voltage measurements for the past week are below. I had issues on 7/22, 7/19 and 7/12 (not shown). we stayed on the boat aother night and I think the 10.2V was briefly while we made coffee. It appears that they were fully charged the rest of the time. My boat also charges from the solar panel so, unless both my alternator and solar panel are bad, I think it's a battery problem.

It's my understanding that Trojans have a life of 5-10 years if maintained well. In real life stuff happens, I tried but I don't think I treated them kindly so I might be on the 5 year side. In any event, I don't have time to replace them before my trip. I'll ensure that the alternator is in fact charging before we leave, I have the solar and a honda generator as backup.

 

[dlochner]

I'm pretty sure they were fully charged. The boat sat on a mooring and was used briefly for 2 out of 7 days. The min and max voltage measurements for the past week are below. I had issues on 7/22, 7/19 and 7/12 (not shown). we stayed on the boat aother night and I think the 10.2V was briefly while we made coffee. It appears that they were fully charged the rest of the timeView attachment 233188. My boat also charges from the solar panel so, unless both my alternator and solar panel are bad, I think it's a battery problem.

It's my understanding that Trojans have a life of 5-10 years if maintained well. In real life stuff happens, I tried but I don't think I treated them kindly so I might be on the 5 year side. In any event, I don't have time to replace them before my trip. I'll ensure that the alternator is in fact charging before we leave, I have the solar and a honda generator as backup.

When batteries age they lose capacity, not voltage. The batteries will charge to the proper voltage and look "charged" which they are. However, over time the capacity decreases. The 100ah battery may only have a capacity 60 or 70 ah or less after several years or some unfortunate deep discharges or lack of maintenance. The telltale sign is the batteries discharge quickly, because they don't have much capacity. This seems to be happening to your batteries. Equalizing the batteries may increase their capacity, but it will not return the batteries to original capacity.

A 20 hour capacity test will yield the actual capacity of the batteries. Note, this is capacity test not a capacitance test which is what the auto parts stores use to test the battery.