I have a universal M25 and noticed that my alternator output voltage was at 14.3 volts with fully charged batteries. I have an ampmeter in line with the alternator output and it was reading 0. I thought an alternator was supposed to output about 13.8volts not at 14.3. Its possible the battery selector switch was switched to the off position with the diesel running recently, and I have read that this could cause problems.
Alternator question
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If you had blown the diodes, you'd know it. Alternators, particularly those with internal regulators, will run up to 14.4 V before declining to 13+ even when batteries are fully charged. Are you experiencing something out of the ordinary?
I went out yesterday and noticed the amp output was at zero after I started the engine. I was expecting some reading as the batteries had been slightly discharged. So I checked the battery voltage and it was reading a standard battery voltage of 12.4. So at that time I thought the alternator was definitely bad.The next day I started the diesel and noiticed voltage was reading the 14.3 that I mentioned , so I am confused as to what would cause this.
#1 You don't want a regulator that puts out 13.8V in absorption. 14.2-14.6V will charge your batteries faster. Some older regulators had a voltage set point of 13.8V but this leads to chronic undercharging which is not good for the batteries.
#2 You really need to address the alternator wiring circuit and remove that ammeter. These circuits are very, very problematic and can actually be very dangerous if left as is. Your entire alternator output runs through multiple feet of 10GA wire to get to the ammeter than through many more feet of 10GA wire to get to the battery bank. Not good! I just did this conversion on an Oday 30 and have done it on MANY Universal M series and 54 series engines.. Simply jump the alt to the starter stud with about 6GA wire and replace the ammeter with a volt meter.
#3 Your problem sounds like it could be a bad connection. Your factory engine wiring harness has a trailer looking connector, on Oday's it's usually near the engine panel but could be anywhere between the engine and panel, and these are a HUGE source of issues. I have a melted one sitting on my bench right now, dangerous!! This connector should be cut out, the wires cleaned and re-terminated with either ring terminals and a buss bar or heat shrink butt splices. Check ALL connections, clean and re-terminate.
#4 The factory ring terminals are famous for breaking under the heat shrink as it was not adhesive lined and they offered very little strain relief.
#5 At full charge with no loads running you should see 14.2V - 14.6V on your alternator. This is a single set point regulator so it will not step the voltage down. Your alternator is either in bulk, which is anything before your batteries reach the regulator set point or absorption, which is your regulators set point.
#6 You can't use those cheap ammeters to determine much. If you like to have an ammeter a battery monitor is a much better device. If your batteries were in fact full or close to it they could have been taking less than an amp of charge current and this would be normal.
If what you say is correct and the problem is in the harness wiring, could this be the cause of the alternator not putting out any voltage, as I was reading 12.4 volts with the engine running.
Yes it can but it could also be a faulty regulator too. The alt on those is very often "key on excite" and this is usually a purple wire to the excite terminal of the alt.. Some later ones were self excite but they bounced back and forth. Also if your alt wire to the bank is buggy then the alt may not be seeing a load. It could also be a bad ground too..
I will check the harness wiring for bad connections.Getting back to your suggestion of removing the ampmeter in line with the alternator output. I disconneted an external voltage regulator that had been installed by the previous owner.I used the 60 amp ampmeter from it and installed it inline with new #8 guage wire from the alternator output to the battery bank.What would be the problem if the wire was sized correctly and the ampmeter was large enough for the M25 alternator
going back to my car mechanic days, we used to start a car with one battery, then take the battery we used to start the car out, and put the dead battery in, so we could charge it on the run. that was with a dynamo, you cant do it with an alterator, when you run an alternator, and you remove the battery, or disconect the battery, you blow all the diodes in the alternator, and the voltage goes through the roof, an alternator, charges in AC, a dynamo, charges DC, but both will charge a battery, you just dont get as much out of a dynamo, but, a dynamo, can run, without puting a load on it, eventually it will heat up and burn out, because the electricity is going noewhere, and alternator, has a regulator in it, made up of a diode panel, and even disconeting the battery when the alternator is running, will flash that panel.
I'd have to disagree, when you disconnect the battery the regulator will still be regulating "IF" you have the voltage sense wire connected to a positive terminal wire the alternator can supply voltage to. It will continue to regulate the voltage and not let it spike. Course most of the auto alternators have no voltage sense wire as that is done internally while a lot of boats with "remote" regulators have to have a sense wire. That may or may not be at the battery.
Most voltage spikes occur when you turn the 3-way to off and the voltage sense attached to the battery terminal sees a floating battery voltage not a charging one. The regulator turns the alternator field up to bring the charging voltage up and continues till the alternator is full fielded. The sense wire sees none of that though and the voltage on the alternator side of the 3-way spikes. That is why you ALWAYS want the voltage sense wire to be on the alternator side of the three way switch.
Most voltage spikes occur when you turn the 3-way to off and the voltage sense attached to the battery terminal sees a floating battery voltage not a charging one. The regulator turns the alternator field up to bring the charging voltage up and continues till the alternator is full fielded. The sense wire sees none of that though and the voltage on the alternator side of the 3-way spikes. That is why you ALWAYS want the voltage sense wire to be on the alternator side of the three way switch.
In conjunction with Maine Sail's #4, here's some background on how 1-2-B switches are and then can be wired.
http://c34.org/bbs/index.php/topic,4949.msg30101.html#msg30101
and
http://c34.org/bbs/index.php/topic,6604.0.html
http://c34.org/bbs/index.php/topic,4949.msg30101.html#msg30101
and
http://c34.org/bbs/index.php/topic,6604.0.html
And with isolators..?
Of course you do not "ALWAYS" need the sense wire on the alt side of the switch because you can simply direct wire the alt and sense wire direct to the bank and delete the switch from the circuit and never again worry about blown diodes..Even if the regulators sense wire is connected directly to the alternator output, there is still some delay in the regulators response time, think milliseconds. In the case of a battery switch disconnecting the load/battery bank it can produce a very fast momentary voltage spike BEFORE the reg can cut it down. The regulator tries to react and cut the spike down but in many cases the damage is, and has already been done, especially if the alt was working hard when switched off.
The diodes don't all have to fail. I have had to repair two alternators this season for partially blown diodes. The alts worked but only at 1/3 or so output because not all diodes blew but some did. I took a video of an 80A Yanmar alt that produced only 35-40A cold with the blown diodes. When repaired she put out close to 95A cold. This owner switched through OFF and knew he did it accidentally. He noticed the drop in current nearly immediately as his banks had been taking 65A or so just prior..
Many alternators do not have sufficient protection internally to sustain a disconnecting of the "load". I have seen Hitachi's, Delco's, Motorolla's, Mando's, Leece-Neville's, Balmar, Ample Power and others all suffer this fate. Balmar fully admits that theirs don't have any protection from disconnecting the load.. Some car alternators do and they use avalanche diodes, don't really know why but they do, as the load is rarely if ever disconnected, but most marine alts, including Balmar's and others do not incorporate avalanche protection diodes.
I have a 55A Motorola putting out 12 +/- amps that is going in for repair in a few weeks when I get to it. Owner passed through OFF with the motor running. I had previously measured the output of this alternator well over 40A hot.. Sometimes they all blow, sometimes they still work but at reduced output, sometimes nothing happens. still not worth gambling with...
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