BAC Forum
General Boards => Technical Support => Topic started by: Mike Groves on May 01, 2015, 12:30:34 AM
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For some time now I've had a 1 volt drop (12.8 to 13.2 rather than normal 13.8 to 14.2) from that measured at the alternator to that measured at the battery (and on my Silverleaf and Dash Voltmeter). How many devices are between my alternator and battery and what are they?
Thanks Mike
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Probably just a battery isolator with diodes in it. The voltage drop of the isolator is about .3V. Wire resistance may account for a bit more. Also check for a bad battery pulling current.
Later Ed
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I agree with Ed. To verify where the voltage drop is, perform this test. Locate the isolator in the battery compartment (blue finned device about 4" by 10" with 3 battery cables going to it). With your multimeter, check the voltage between ground and each cable. The alternator is 14.2 to 14.6. the house battery about .8 volts less and chassis batterys about the same. All contingent on loads applied, clean cables and the age of the batteries.
Gotta love the mystery of "Tricity" Fred
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Ed and Fred, thanks, I guess the isolator is the only device between the alternator and the batteries. I'll try probing the voltage when I get a chance (Coach is at the storage facility).
Some other clues are the following:
Chassis Batteries and alternator (rebuilt) are new and this issue was discovered by the guys that rebuilt the alternator. I'd had the alternator rebuilt by Oregon Motorcoach, along with new Chassis batteries replaced, in April last year, then went on a cross country trip. The battery charge rate was in excess of 14.8 (according to Silverleaf). Prior to alternator rebuild, and chassis battery replacement I'd gotten high voltage alarms through the Silverleaf, but don't remember any after replacing and rebuilding charge system, so I thought all was well.
After reaching the east coast and upon my return west, I got to Wisconsin before I saw that suddenly the alternator wasn't charging any longer. I fretted for a holiday weekend to end, so that on Tuesday I could get it looked at, but suddenly it was charging again, so I continued, and got all the way to Yellowstone before getting the warning again from the Silverleaf of undercharging/no charge out of the alternator.
Limped my way through the park using the generator, then stopped in Idaho. That's where the guys told me that "on the bench the rebuilt alternator was giving 14.2V which was spec for the alternator, but as soon as it was placed in the coach, it would give over 15V and they said that sort of thing would fry the alternator and that's probably what happened. They verified that the chassis batteries were fine (up to charge), so that wasn't what was calling for more volts. They weren't familiar with the coach, so what they did was craft an output limiter from the alternator using some sort of electrical wizardry to limit its output to 14.2, and they noted that there was a 1 volt drop to the batteries (13.2 was the max since the alternator was limited to 14.2), but told me by limiting the output of the alternator it would not burn out again. So, I've had this issue since about June of last year, but have been happy with the charge rate which runs from 12.8 to 13.2 on the Silverleaf without causing an alarm condition.
I've read others' postings about having outputs of over 14.2, and I've read all the warnings about running the generator in the morning to pre-charge chassis batteries, but even though that would explain the high demand placed on the alternator, it doesn't explain the voltage drop to the batteries, so I guess I need a new isolator to go back to perfect.
I looked at removing it, but boy that looks like either a lot of work (mainly to get to the bolts) as mine is sandwiched in between two surfaces, or I need specific tools. Anyone done this? I'm not sure if a 2000 year coach has the same setup as mine in the battery compartment as to location of the isolator, but it probably does.
You can see the bottom left corner of the isolator barely visible in this jpeg image -
http://coach.quickreckoning.com/BatteryAndServiceBays.jpg - the bolt visible is the easy one to get to. :D
Thanks again Ed, and Fred.
Mike
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Mike,
It is pretty rare that the isolators go bad and the isolator has no way of raising voltage so if the alternator is producing too high a voltage it is usually the regulator in the alternator or a wiring issue where the ground or sense lead has a bad connection. The isolator either conducts with a small voltage drop or it is open and will not conduct any current. There should be no need to add "external wizardry circuits" to control your voltage. I would probably look for someone who has decent knowledge regarding alternators, isolators, and batteries to sort out what the root cause of your problem is and resolve it. It sounds to me like something is still not right with the alternator or its voltage sensing connections which require a good ground and a good reference voltage connection usually tied to the battery + lead.
Later Ed
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Ed,
Thanks for your post. I brings up two concise questions in my mind that I hope you can answer from your coach experience. I know its a little different than mine but perhaps the same in these areas.
Where does the battery level sensor measure the battery level to report it back to the alternator? Where's it coming from?
And two -
What is the maximum voltage output rating for this of this alternator, and how low does the battery voltage have to be to "tell" the alternator to go max rating? Said another way as an example, if the alternator senses 14.2 volts in the battery does it generate 14.2 volts or does it reduce to 13.8, what does it do?
Oh, and a third, for anyone, have you metered your alternator at its output, and compared that to your battery? Are they the same (assuming fully charged batteries)? What is the difference in yours - mine is 1 Volt difference.
Thanks to all.
Mike
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Mike
I had a very similar alternator problem on our previous Beaver. The voltage output was very high, 15.0 to 15.7 at highway speeds. When we were around idle to approx. 1200 rpm voltage was around 13.3. I do know the lead acid batteries were overcharged, electrolyte solution all over the batteries.
Went to Southeast Power in Altamonte Springs (basically Orlando) FL. and they replaced the sense wire and added a relay to prevent battery power from feeding back to the alternator when coach was shut down. The sense wire went from chassis batteries to the alternator with the relay in there. No more problems, voltage was solid at 14.2 volts.
Hope this helps.
Larry D
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Mike,
Some alternators like a Leece Neville with a Duvac system (which were commonly used in Beaver coaches) had a remote sense wire that most likely went to the chassis battery side of the isolator so it was sensing battery voltage close to the battery after any diode voltage drop within the isolator. Most alternator brands do not have the remote sense lead and sense the voltage connection at the alternator, so if someone changed that alternator out you may not have the remote sense. If so that is not a big deal. It would mean maybe .3V less on average gets to the battery +.
There are fixed voltage regulators and adjustable ones in the alternator depending on alternator brand and the era that it was built. I had my Leece Neville rebuilt and the new Leece Neville regulator went from an adjustable version to a fixed version. The new one puts out about 14.4V perhaps a bit more.
The intent is to have the voltage held at a constant and the current output varies to support the charge and chassis use load. That does not mean that you always get 14.4 V at the battery, there is voltage drop that will vary. The higher the load the more voltage drop in the wiring from the alternator going to the battery. At 100 amps you might get 13V and at 10 amps 14.4V. The other factor is temperature, if the alternator is putting out high current and it is internally getting hot, the alternator will derate itself and put out less current which could result in a lower output voltage also. The alternator will probably not get near 14.4V looking at high load of a discharged battery bank and may slowly rise from around 12.8V to the 14V region over time as the battery charge comes up and the load diminishes.
The net of all this is you probably should be seeing between 13V and 14.5V at the batteries with the engine running above idle, no external inverter/charger on (coach not plugged into 120V) as long as the batteries are good and are at a decent charge level, and less voltage possibly if they are not. I would not be looking for an exact voltage of 14.4V or 13.8V, just a usable range and consistent charging performance. 13.8V to 14.4V is typical and I have seen it even a bit higher for for some alternators, perhaps 14.8V with charged batteries.
Later Ed
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Mike,
Assuming that you still have a Leece Neville Duvac alternator, there are 4 wires that connect to the alternator, two large wires (one for output and one for ground), and two small (14 to 16 gauge) wires. one of the small wires is a sense wire that is connected to the chassis batteries, and the other one is from the ignition circuit. If the two small wires are reversed, it can cause the problem that you experienced. However, if they are not reversed, you have a bad connection in the sense wire.
If you are not comfortable in trouble shooting the alternator circuit, find an automotive electrical shop that is familiar with an Duvac motorhome alternator system to have it repaired. With you alternator producing 12.8 volts at the batteries, your batteries will not be fully charged.
Gerald
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Hi Gerald,
When the alternator was last rebuilt, and the gentlemen did that special wiring that prohibits my alternator from putting out 15.8V and burning up in the process, I found that the rear engine door fan no longer worked, so I found a wire unattached by the alternator (which was to drive the fan) and hooked it back up to a post and its now working again, so my assumption is that wire is from the ignition circuit because it now operates the fan as it once had, ie, fan runs all the time, then after engine shutdown it times out after about 20-30 minutes.
They attached the special wiring getup to the other post I believe so that must be limiting the sense to the alternator and thus limiting its output voltage to 13.8 to 14.2 (of which I read from 12.8 to 13.2 on the silverleaf and if I voltmeter the chassis battery). I am not sure but part of this wiring change may also contact the positive post on the alternator.
Anyway, my original goal of this posting was to figure out why, if the alternator was pushing 14.2 was the battery only showing 13.2 so that must be across the isolator as there is nothing else between them. I wasn't comfortable removing that isolator as it was so hard to get to with the tools I had.
Mike
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Mike,
I am not sure that you need extra getup wiring here. It may be that your sense wire is now on the wrong side of the isolator (alternator side). 15V at the alternator is OK if it is 13.8 to 14.4V at the battery post.....that is the idea with a sense wire. Maybe the tech can detail the wiring change that he did and you can post it so we can see what is up.
Later Ed
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Ed,
I guess I could find the paperwork and give them a call, but its been a whole year since they did this. They would probably remember the event because they worked mainly on school buses and I brought them a coach, but I doubt they would remember how the patch wire works. I do remember them discussing diodes.
It does work. It fixes the output to no more than 14.2 volts and I haven't burned the alternator up in a year which is much better than burning it up in 2 months which it did the first time, and it was bad when I bought the coach, so it probably wasn't a new problem.
I agree with Gerald that I'm not getting the chassis batteries fully charged but then again, I am now parking more than I am driving so it does get charged when I am plugged in. One mechanic told me, I'm not hurting myself as 12.8 to 13.2 is higher than 12V and I haven't had any issues starting the coach.
I guess the guys that did the rebuild would disagree with you when you say 15V is ok (mine was giving out 15.8 or so and to them that definitely was not ok), and that's why they fixed it at 14.2 max which according to them was the max output this alternator should be pushing. I guess I understood that logic as why push more than 14.2 to keep a battery at 13.8 (which is what I've always thought chassis batteries were).
I know when my generator is running, the house battery charge ramps up to about 14.2 or 14.3 during the charge cycle on the inverter, before eventually coming down and leveling off at 13.5V at the float setting. So I don't know why I'd want the alternator giving more than that.
My issue is more with why the 1V drop as I am happy with the limits on the output. And I think we've basically all agreed it has to be through the isolator since there's nothing else between the alternator + side and the battery.
Thanks,
Mike
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Mike,
I have never seen an isolator that had enough resistance to cause a 1 volt drop in charging voltage without failing. Also the resistance would have to be the same on both sides of the isolator which is almost impossible or your house batteries would be charging at 14 volts while the chassis batteries are at 13 volts.
Voltage output is not what burns-up an alternator. Amperage output is what burns-up an alternator. However, if the high voltage is reaching a battery bank, they will take more amps so the issue is how many volts are reaching both banks batteries. I still say that your alternator needs to be properly repaired.
Gerald
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Mike,
The way this is supposed to work is the alternator sense wire looks at the battery voltage and compensates for voltage drop through the isolator. As Gerald pointed out 1V is too much drop for a good isolator. When I said in my post that 15V at the alternator is fine if the batteries are seeing about 13.8V to 14.4V, the 15V will not burn out an alternator as long as the voltage level is good at the battery and the amp load is not too great due to a bad battery forcing extra load.
The reason I bring up the "getup" and understanding it, is lets say they added a series of heavy duty diodes in series with the output lead in order to drop the voltage getting to the battery, that could account for a 1V drop. At this point I guess I am not sure if you have a Leece Neville alternator with a Duvac system, not sure if the sense lead is seeing battery voltage, and what has been added circuitry wise to give you the output that you are getting at the battery bank, which seems a little low but probably in the scheme of things should be adequate. Without knowing what you have installed and how it all is supposed to work makes a lot of this speculation...we know how the original system was supposed to work.
One thing that could be helpful is to take some voltage measurements with shore power off and the engine running. As always only take these measurements if you feel safe doing so and are physically clear of the belts while doing so. Measure the alternator output post to ground (large + lead), sense wire to ground, the center post on the isolator to ground, then each of the two other isolator posts to ground, chassis battery + to minus posts, and the house 6V pairs in series + to minus posts. They should read in the +13V region also. This should tell us where the voltage drop is occurring or if the alternator output voltage is low. Also photograph the "getup" and tell us what alternator leads it is connected to.
You could elect to hunt down a good alternator shop and have them sort this out if you are uncomfortable with these measurements and still want to get to the bottom of this. Hope this helps.
Later Ed
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Thanks Ed,
I'll have to wait until I go back to the storage lot, but I can tell you I've already taken two of those measurements, the output voltage is rock steady at 14.2 initially, and the chassis battery is 13.2 hence my initial question of what's in line (in between) the alternator output of 14.2 and where it connects to the battery.
Anyway, for now, I have some action items but they'll have to wait for my return to the coach.
Anyone going to be at Pacific Shores any time from June 9 to June 21. I'd love to meet some members of the forum, and if also owners at Pacific Shores, that would be great as well. I am studying all the owner information to catch up on the history of the resort.
Thanks everyone,
Mike
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Mike,
I have never seen an isolator that had enough resistance to cause a 1 volt drop in charging voltage without failing. Also the resistance would have to be the same on both sides of the isolator which is almost impossible or your house batteries would be charging at 14 volts while the chassis batteries are at 13 volts.
Voltage output is not what burns-up an alternator. Amperage output is what burns-up an alternator. However, if the high voltage is reaching a battery bank, they will take more amps so the issue is how many volts are reaching both banks batteries. I still say that your alternator needs to be properly repaired.
Gerald
Ok, let's assume then that my isolator is not working properly. While running down the road, with my monitor on (the CMP), the coach batteries are not getting any more than 13.2 volts as well, so that value matches my silverleaf chassis battery value. Those two values do seem to parrot one another. Does this mean the isolator is simply not working at all? Is that what you're saying?
I may have confused you when I talked about the coach batteries charging at 14.2 or so while running the generator or plugged into 120V. I never said that they were charging at 14.2 from the alternator while running only the engine. Rather, to be very clear, they MATCH what the chassis battery is showing - ie 1V less than alternator output which varies from 13.8 to 14.2 but never more then 14.2 (rarely see less than 13.8 and only for a short period - pretty steady in between those two measures, which I consider normal alternator output).
For clarity, obviously I don't have a real-time sensor for the alternator output, but under the conditions noted on my monitor gear (13.2), when I have gone to the back and measure alternator output to ground, it has always yielded the 14.2v. So, I am in no way saying that I can measure all simultaneously all the time as I can with chassis and coach batteries using the CMP and the silverleaf.
Thanks,
Mike
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Mike,
The purpose of the sense wire on the alternator is to deliver the desired voltage to the batteries. With a Duvac alternator, any resistance in the isolator is disregarded because the alternator voltage regulator is reading the voltage at the batteries instead of it's output voltage at the alternator. Apparently the shop that worked on your alternator disabled the sense wire circuit on your alternator if it exist. Most coach owners have no idea what the alternator output voltage is at the alternator because they are looking at the gauges that read output at the batteries which should be around the 13.8 to 14.2 volt range.
Your isolator is working if it is passing current through from the alternator to the batteries, not getting hot, and not letting one battery bank discharge the other bank. However, if the cable between the alternator and the isolator is good with good connections on both ends, and both battery banks are receiving the same voltage at 12.8, your sense wire circuit is your problem if you have a Duvac alternator. The key here is with your alternator, is it designed for a Duvac electrical system.
If you do not want to repair your sense wire circuit, you can replace the battery isolator with a good quality "Bird" system that will directly tie your alternator to your chassis batteries and remove the need for the isolator and sense wire. I would recommend a "Bird" system like the Blue Sea system instead of the Intellitec system that Monaco used on late model Beavers. A "Bird" system will allow you to use the less expensive alternator like trucks and busses instead of the more expensive Duvac system used on motorhomes.
Gerald
Gerald
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Gerald,
I think we agree that other owners have no idea what their alternator is outputting.
They only know what their batteries read, and those values are as high as 14.8 from what I've read. And that's about what mine read when I had my chassis batteries replaced and alternator rebuilt in April of 2014. Based on what I'd read, I felt this was normal voltage to see on the silverleaf. I now think that the alternator output at that time was about 15.8V, and I would not be surprised if other owners measure their output voltage that they would see something similar.
Since V=IR, and assuming resistance is a constant, a higher voltage will mean a higher amperage as they are directly proportional mathematically. My newly rebuilt alternator burned up during a 2 month trip across country.
Since being rebuilt the second time in 2 months (rebuild again in June 2014), the gents who repaired mine the 2nd did measure the output voltage (something not done typically because the rebuild is farmed out to someone else by a coach maintenance facility and therefore can not be tested on the vehicle by the rebuilder), and found it to be in the 15 to 15.8 range but only 14.2 on their bench test, I do know what mine was outputting, and also after they did the "fix" I know its now outputting 13.8 to 14.2.
So, I am still wondering if any owners will put a meter on theirs and see what the output post is reading. I wonder if theirs will show 15V or more, and if perhaps, this is the reason there has been so much talk of alternator rebuilds/replacements for these coaches. I do know that the other theory is that dry camping causes too much current to be generated by the alternator and thus burns out the alternator and that the fix for that was to run the generator in the morning or while driving to mitigate this issue. This was an actual precaution I used during my 2 month cross country trip, but it didn't save my alternator.
Thanks,
Mike