Spent the weekend at Catalina Is which gave us a chance to evaluate some things. We had noticed last year that the house bank would run down quickly (~5 hours) and our rule o'thumb of an hour of engine in the morning and evening was not keeping up. We had the batteries checked at the end of the season and they were fine. The voltage at the battery with the engine on is 13.7 V which seemed fine. I installed a battery monitor for this trip to see what was going on (Found a pretty good V, A, AH meter with a shunt made in China, cheap ~$40, on Ebay).
Our alternator is an 8MR2049 (50 amp?). When the engine started and the house batteries very low, it charged that bank at 7.5A, but within a few minutes dropped to 2A. The alternator was only seeing the house batteries at the time. This does not seem like normal behavior, but it does explain what we've been seeing on our cruises. Any ideas?
As an aside, we also purchased a 120W solar panel and PWM charge controller ($150). That worked great. It put out a steady 5-6.5 A with just a couple of adjustments during the day. It was enough to run the fridge all day with a couple of amps excess to the batteries.
Alternator trouble? Maybe not. Please advise what engine rpm you were running when you got those amperage readings. Running at idle, or even 1500 rpm doesn't always produce output even with low batteries from a night of use and the batteries able to accept high amounts of current. 13.7 is a low voltage for acceptance charging, but also please advise when this voltage was seen: at startup at idle or when full out running, etc.
Should have been more specific... We charge at ~2000 RPM. The house batteries are 2ea 80 AH Group 27 maintenance free wet cell, deep cycle. When under way, at full throttle, it exhibited the same behavior.
I did not see an adjustment for the set point on the alternator. Is there one I'm missing? What is the proper set point?
2nd : As Stu said 13.7V at 2000rpm is low if the batteries are discharged. It would be better to see 14 - 14.2V at that RPM.
You said you installed a battery monitor. When I am charging batteries I primarily look at Amperage and then look at Voltage.
What was you amperage reading?
Ron's on the path...
What amperage at what voltage at what rpm is the information we need. From what you've said so far, it appears you have a stock 1987 or so OEM internally regulated alternator on an M25XP engine. Is that right?
When I started the engine, I switched to the house battery bank. Ran the engine up to ~2000 RPM and observed ~13.7 V(approximately) and 7.5A current. Within a few minutes (less than 5) it was down to 2 A at the same voltage. The engine is an M25XP with a stock alternator and internal regulator.
I should also mention that with the solar panel alone I was seeing 14.2-14.3 V @ 6 A on the monitor- also suggesting the set point of the alternator is too low.
It could very well mean that your batteries are FULL.
Most definitely NOT full. The batteries had been running the fridge all night and the voltage had dropped to ~11.7V. Also, the batteries were able to take everything the solar panel could put out. BTW the fridge will not actually run properly below 12V , it will just cycle the fan repeatedly and the compressor shuts off as soon as it starts-another interesting tidbit.
So, then, unless there are wiring issues, you need to check the alternator. Right?
Yup. I'll check the wiring by looking for a voltage drop under load. Can the regulator setpoint change? Is that a failure mode? Somehow seems unlikely.
2ndw,
Unless you have changed your regulator, we have to assume you have an OEM setup. Unless you take it to an alternator shop, those old OEMs aren't "user adjustable."
Since your monitor is new, you may not have been in a position to know what USED to be going on with your alternator before this trip.
You might also have battery issues, but your solar system seems to be working.
Sounds more like an alternator issue. Maybe as simple as a regulator failure.
How's your belt tension?
Hmm. I think the belt tension is ok. If there was a lot of slipping I'd notice it. But you raise a good point about the rule of thumb. There are two additional variables in recent years. 1) The batteries were replaced about three years ago (could their acceptance be different than the old batteries?) and 2) the refrigerator compressor was also changed at that time. If the cycling of the fridge is a "feature" to protect the batteries, they may not be discharging as deeply as the old ones and therefore not charging as fast at the low setpoint. Now that I have the monitor, I will do a thorough discharge this weekend and report back next week. Either way, it seems that with the current situation, the alternator is not charging efficiently and should be addressed.
2nd : It sounds as though your voltage regulator is seeing fully charged batteries?!?
Dumb question - do you have the "wiring harness upgrade" installed?? (see critical upgrades)
2nd : Also rereading your #7 reply, 11.7v is EXTREMELY low (infact they maybe flat!!). I'd even guess that the voltage part of your "new" monitor isn't correct.
I'd recommend that you check the "new" monitors voltage readings against a good multi-meter.
My thought
Thanks for the ideas. The new monitor was checked against our panel mounted voltmeter and a handheld digital multimeter (also used to calibrate the current readout). All agreed within 0.1 V. Our house bank has two, 80 AH batteries. When they were tested at WM last fall, they had ~75% life left, so 2 batteries run down a little more... 0.7x160AH =112AH capacity. The fridge +other things are about 5A so 10 hrs would be 50AH or 60% of remaining capacity. I do not have the discharge curve for these batteries, but using an old curve for a lead acid battery I found on the web, the state of charge could be between 25-50% for 11.7 V for a discharge rate between C/20-C/10, so 11.7 V is low, but not out of the realm of possibility, particularly if the batteries have lost some more capacity or are out of balance.
ps. We have upgraded the harness
Quote from: 2ndwish on April 30, 2013, 11:20:35 PM
Thanks for the ideas. The new monitor was checked against our panel mounted voltmeter and a handheld digital multimeter (also used to calibrate the current readout). All agreed within 0.1 V. Our house bank has two, 80 AH batteries. When they were tested at WM last fall, they had ~75% life left, so 2 batteries run down a little more... 0.7x160AH =112AH capacity. The fridge +other things are about 5A so 10 hrs would be 50AH or 60% of remaining capacity. I do not have the discharge curve for these batteries, but using an old curve for a lead acid battery I found on the web, the state of charge could be between 25-50% for 11.7 V for a discharge rate between C/20-C/10, so 11.7 V is low, but not out of the realm of possibility, particularly if the batteries have lost some more capacity or are out of balance.
By industry standards your batteries are dead. Anything less than 80% of new CCA or MCA is considered dead. WM uses Midtronics equipment and they should have let you know that 75% is not a passing grade for batteries. Dead batteries don't accept current like newer ones do so this could be
part of your problem.. I still suspect a wiring/connection issue. You ideally should have your alt checked out too because you should have a higher voltage.. It is possible to lose
some diodes but not all....
Spent a couple of days looking into this and here is what we found.
1) Had the alternator tested at a shop and it was bad. The max current they could get out of it was 20 amps and the voltage was 13.7 or lower. Replaced it with a Leece-Neville 65 amp unit with a 14.3 V set point. The batteries now charge at 9 amps and I was able to get the alternator to put out 21 amps (at 14.05 V as measured at the alternator). Also, the tach started reading correctly (it was off by some factor before).
2) The batteries are likely shot. I ran them down to 11.9 V and let it charge overnight on the charger and only got 13.5 amp hours into the batteries (should have been closer to 80 AH). One oddity is that when we operated the solar panels, we got more charge than this...so...
3) The battery charger (Lewco)does not seem to be able to charge beyond 13.7V, which may be contributing to the battery problem. As a side note- if we replace this, is there any particular reason to go with Promariner ProNautic and not the ProSport series- the specs are similar for our application and there is a big $$ difference?
4)While mucking with the batteries I discovered another issue which seems related. While there is a very good ground return from the batteries to the engine, the ground to the service panel comes through a single 10AWG wire. With 9A running, there was a drop of 0.3V between the battery and the panel, so the fridge say, sees this additional drop which makes it cut out early as a result of its battery protection circuit (the start current for a Danfoss compressor is 11A). This also explains why cabin lights dim so much when something is turned on. When I checked the wiring diagram in the owners manual, they confirm that this ground is provided by a 10AWG wire (although where it is connected is unspecified).
We were expecting to find one problem, found several.
Definitely upsize the ground to the service panel. It should be the same size as the positive feed since it will carry the exact same current load.
2nd : Here is "rule of thumb" on battery voltage vrs % charge levels. I published this in the mainsheet tech note long ago!!
12.75V = 100% charged and 11.75 = 00% charged
( the % charge changes 5% with every .05 V -- ie. 12.25V = 50% charge).
Quote from: Ted Pounds on May 05, 2013, 01:19:34 PM
Definitely upsize the ground to the service panel. It should be the same size as the positive feed since it will carry the exact same current load.
Ted- It is not as simple as matching the gauges. The full starter current goes through the Perko on the panel, but the heavy ground is connected directly to the engine block. The panel itself requires a ground wire large enough to accommodate the service load, which is much less than the starter current. Still 10AWG seems quite small for loads which can reach 20A. I wonder what others have done?
Good point. I didn't think about starter loads. But I definitely agree that #10 seems a bit small. However, since I sold my boat a few years back, I don't remember how my boat was set up...
2nd : As the replies have said "You can't have too many grounds" !!
I ran a #4 wire from the grounded alternator case (along with my 2 positive wire) direct to the batteries.
Then to insure there was a good ground at the main electrical panel I ran a #8 ground wire from the batteries direct to the DC buss bar just above the Perko selector switch.
A few thoughts