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Old 09-02-2004, 01:40 PM   #1
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Smile Urgent! Alternator/isolator wired incorrect!

See battery isolator thread for background. The Airstream manual shows a red wire, in series with a diode, going to the Alternator sensor. My diode shorted out and I had all kinds of problems with both the alternator and the isolator. I checked with my dealer, Chevrolet national, Airstream etc. etc. No one new what the red wire was for or what it was doing. In my coach it was blowing out fuzes in the ignition circuit. All answers are on the www.surepower.com web site (they make the isolators). Our motor homes (from 1985 to 1993) use the Delco CS series of alternators. These units require a voltage input from the engine battery which is used by the regulator to adjust the alternator output voltage. I spoke to a Sure Power engineer and he could not figure out why Airstream hooked the sensor terminal of the Alternator to the alternator output. I suggested that what they did was put a diode in series with the sensor wire to get a voltage drop so that the regulator would hold its output just above that drop. He agreed, however, he said that was the wrong way to do it. I threw the diode away and wired up my system per the Sure Power Technical Note (Multi-Battery Isolator Application & Installation Instructions). Wow I am getting over 14 volts on start-up which drops as the batteries charge up. I did not need a new alternator or a new isolator just had to wire the system correctly. Good Luck Try it you will like it.
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Old 09-02-2004, 01:46 PM   #2
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Great Info

Thanks for the update, and the website with the solution.

I have to wonder, though, if Airstream built a "high voltage" link into the system to help the 'fridge stay on line with 12 volts when the engine is running. I "think" (don't remember for sure) that the 12 volt element will not come on until 12.8 volts is sensed.
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Old 09-02-2004, 02:59 PM   #3
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I guess my older coach doesn't have that wiring(?) I replaced my alternator with a 135 amp and battery isolator with a 200. Have been happy with the charging rates ever since. No worries.
In fact,, the two best things I did, was the above upgrade, and the "Hi torque starter upgrade. Sure has made travelling more secure.
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Old 09-02-2004, 04:04 PM   #4
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Quote:
Originally Posted by ALANSD
I guess my older coach doesn't have that wiring(?) I replaced my alternator with a 135 amp and battery isolator with a 200. Have been happy with the charging rates ever since. No worries.
In fact,, the two best things I did, was the above upgrade, and the "Hi torque starter upgrade. Sure has made travelling more secure.
Right. From about 1986 and older it is a different regulator and it does not have a voltage sensor terminal. Also you usually have a 3 terminal battery isolator which works fine with your alternator.
The 1986 and later changed the voltage regulators built into the alternators in that they sense the engine battery voltage and adjust the output accordingly.
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Old 09-02-2004, 04:10 PM   #5
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gotcha...thanks for clarifying for me
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Old 01-08-2005, 09:56 AM   #6
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Alan,

The Chevy dealer has told me the alternator is bad and not charging my batt. I asked him to put in a higher amp one than stock, which is 80 amps. he said it's the biggest he can put in and won't go higher amp due to wiring, etc...
How did you manage over 100amps?
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Old 01-08-2005, 12:44 PM   #7
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Alternator and a battery question

I bought mine from the same people I got the aluminum starter from in Dallas. WWW.4Alterstart.com
The starter was so good I went to the same source for the alt.

they build their own in the standard GM case, and I upgraded to a higher rated isolator I found that would handle the output. It has worked like a charm for 18 months or more I guess.

I do have a question regarding my Optima coach battery. I notice the voltage on it will drop to about 12.4 or so over a week of non use, even with the ground disconnected. My chassis battery which is an autozone cheapie- holds at 12.7 all the time, and is connected.
I can't see any drain on the optima, but wonder if it needs a better charge when sitting. I use a 2 amp trickle or a 15 amp higher power to keep it up.
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Old 01-08-2005, 06:54 PM   #8
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Just FYI, those alternators were designed only to keep the battery charged, not to charge one. What that means is that the increased load (and internal heat) can cause premature failure in the later model alternators. Maybe Airstream put a diode in the system to keep the alternator from cooking itself trying to charge the battery. That is the only reason I can see why this might be done.

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Old 01-09-2005, 10:06 AM   #9
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So, since my MH sat for two weeks while being worked on, then maybe that's why the battery is dead. They told me that they charged my batts full in the morning, test drove around awhile, then when I'm supposed to pick it up late Friday, the battery was dead! That's when I was told that the alternator didn't keep the batt. charged. I think it may be that they didn't charge it all the way. My MH always started right up before taking it to them. They said this can happen...one day it works, the other, it's dead.

Anyway, they said it looks like I need a replacement and due to the access to this thing, it'll be @ $650. The part is about $200., but they go by book labor. It'll be a GM rebuilt with warranty. They wouldn't consider my buying an after market and having them install...liability. And I ain't doing it myself!
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Old 01-09-2005, 04:33 PM   #10
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Quote:
Originally Posted by Astrodokk
Alan,

The Chevy dealer has told me the alternator is bad and not charging my batt. I asked him to put in a higher amp one than stock, which is 80 amps. he said it's the biggest he can put in and won't go higher amp due to wiring, etc...
How did you manage over 100amps?
Got to love stupid people that don't know how or are too lazy to make a change. Here this dealer could have made few extra bucks with a simple upgrade.

If you want to go to a larger alternator the thing that would need to be changed is the gage of the wire between the alternator and the battery. Thats it in a nut shell. The rest of the wiring is going to be fused and not be able to exceed its max rating without blowing the Fuse or Fusible link.


GM used two different wiring set up over the last 30 years. On most vehicle the main battery cable will run directly to the starter. At the start will be the harness feeds for the Fuse box hot, Fuse box IG and alternator. On the RV or High amp alternator variating the simply ran a second 10 or 8 gage wire off the Alternator directly to the AUX pig tail on the positive battery connection.

Somebody had made comment about somebody wiring the Field circuit directly to the Positive battery output. That can be done but the risk is a slow drain. Basically the field will stay hot and it has the potential the have an electrical bleed back through the armature.

There are "One Wire" alternators that will not need a Field charge to excite the alternator into charging. They have an extra diode to prevent the possibility of voltage bleed back to ground. If its not listed safe to wire as a single wire it would be best to make sure the field wire is wired through ignition so that it is only energized when the key is on.

In a dual battery set up it is common that some isolators also will provide and connection for field or will list a Field dependent alternator wiring diagram as was noted above.

A tip for alternator upgrades is look at the late 80's truck line. Trucks like K30 crew cabs, 3/4 ton suburbans etc came with a single pulley 105 amp alternator stock. If your sourcing then a 1988 Suburban 3/4 ton with 454 would be a good one to tell the parts guy.
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Old 01-09-2005, 07:03 PM   #11
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Quote:
Originally Posted by 59toaster
Got to love stupid people that don't know how or are too lazy to make a change.

Somebody had made comment about somebody wiring the Feild circuit directly to the Positive battery output. That can be done but the risk is a slow drain. Basiclly the field will stay hot and it has the potential the have an electrical bleed back through the armature.
A very quick and simple way around this, is to hook the Field wire to the input (ign) wire lead on the distributor. When you turn off the ignition, you are shutting off power to the field. So, no draw. I would recommend something in the way of circuit protection, although the Field wire doesn't normally draw much power, just enough to excite the circuit.
And, if you want to, GM in later years ran a charge wire directly to the battery, rather than down to the starter and back to the battery, there is less voltage (and current) drop this way.

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Old 01-10-2005, 09:39 AM   #12
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WHOAH, 600 bucks for an alternator?? Sorry but that is too painful. I would think you could order the high power job and get some local mechanic to put it in for you. I changed out the alt and the wires on mine (for heavier duty wire as mentioned above) and it took less than an hour, a few tools, and little hassle other than a stubborn bolt.
Now I know not everyone can do their own work , but there must be a better way.
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