Wire Size for Alternator??

[rv_safetyman]

My problem is that my house battery alternator is not delivering very high amperage.  Let me give you some background:

I have installed a 12V alternator for the house battery bank.  It is a Leese Neville and is supposedly rated at 220 amps.  The first unit I installed was a Delco 22SI and was rated at 150 amps.  I ran number 6 wire to the battery bank (both positive and negative) - distance about 20 feet.  The 22SI would not charge more than about 30 amps (it was a new unit).  The voltage on the Delco seemed very low, even if the batteries started out at fairly high state of charge (don't recall seeing it over 12.8 volts).  I took it to an alternator shop and they said it had low output.  They put the LN on the tester and it almost drug the large AC motor down to stall.

However, LN also does not charge at a very high rate (and our batteries got down to about 50% before we hit the road from Quartzsite).  It appeared that I was only getting a net current flow of about 30 - 40 amps for short periods, often less -- as measured by my TriMetric (generally the current draw while we are on the road is about 20 amps draw, so the combination of the solar and alternator may have been 50 amps in).  The voltage seemed to be better and was around 13.2 after about an hour on the road.  I have checked the connections and they are good (replaced a couple of them).  The alternators are both 1 wire, and I have to boot the rpm up to get it activated, but I can see the voltage and amperage jump up.

One other factor is that the solar cells are also trying to charge the battery and that could mess with the alternator system.  On the next leg of the trip I will disconnect the solar to see if that affects the system.

As I began to think about the issue, I focused on the number 6 wire.  It seemed to "look" good, when I grabbed it out of my wire supply.  But, as I explore wire ratings for 12V/20 feet/200 amp the tables would suggest I should be using 2/0 (welding cable).  I have looked at several alternator installations with alternators in this size range and they do not use nearly that large of wire.  Before I invest in larger wire (have you priced copper lately?) I would like to probe the "intelligence bank" of this great group and see what wire size you think I should install.

If you have any other thoughts about why my charge rate is low, I would appreciate the input.

Jim

[DrivingMissLazy]

Jim, for reference, #6 wire is what is recommended for use as a 50 amp shore cord. I think it is significantly undersized for a 220 amp alternator.

90 degree C. rated wire good for about that amperage should be about 3/0. You are way undersized for that system. 

Richard

[gus]

An alternator will normally produce as many amps as the load demands up to its limit. Amps drop off as the charge builds up.

I cannot imagine a load that would demand the full 220a.

It appears to me that 30-40amps is plenty to charge a battery bank. I don't think I would want more than that if the bank was only about 50% down, the slower the better.

My 160a LN sometimes won't start charging until after the first 30 - 50mi when I first start out in the morning. The only time itever failed me was when the belts got too loose.

[TrevorH]

One cheap way to get some heavy guage wire is to buy a set of heavy duty jumper cables.  I got a 20' set that used 0 gauge wire for $29.99.  So thats 40' of 0g wire.  I couldnt find it cheaper. 

[JohnEd]

Jim,

This is a rare opportunity for me to do some pay back.  Why just today and only a few hours ago i was in my bud's alternator rebuild shop and jaw boning about ......you guessed right.  He related a problem and idiosyncrasy with "SINGLE WIRE" alternators.  Seems they want to see some battery voltage BEFORE they will put out.  Like some women about money....I didn't say that....family show. 

Here is the rub.  You put an isolator in the charge line and the alt doesn't see the voltage.  You have to spin it up real high to let the minuscule residual magnetism in the rotor start things off.  The built in regulator is the culprit on this problem and others.

I wanted guidance on getting max charge to my bats.  I knew that the isolator was dropping voltage and all the other connections to boot were doing me a little harm.  I wanted to know if I could relocate my regulator "PICK UP POINT" to my battery and get the system to regulate the voltage to what the battery needed.  The answer of course was YES, AND THATS FINAL.  He is a kidder.

I have a remote regulator and I can adjust the full charge voltage to up to 20 volts.  Learned that accidentally and luckily I was watching the voltmeter and not the ampmeter.  It looks like you are SOL with a one wire system but stay with me here.  I asked Rick if I could make the one wire system a remote sense system by taking the regulator + wire from the + alternator terminal and running it straight to the battery and the answer was yes.  So there you go Pilgrim....problem solved and you don't have to buy anything but a length of wire the same gauge as that on the alternator.  Not big!

Your LN alternator has a tiny hole in the rear over the regulator.  That is the hole where you insert the screw driver to "ADJ THE ALT OUTPUT VOLTAGE".  Oh, be still, my beating heart.  Someone else will have to tell you what the proper charge voltage is for a deep cycle.

I think this should be clear for a guy with your background but I may not have done a good job of "splainin" it.  Feel free to call me at 541 915 0832 for in person confusion if you like.

Good luck and thanks,  Your answer about my extinguisher volume is ?

John

[rv_safetyman]

Hi John.  It is late and my brain is fried from some additional research.  I will take a better look at what you said in the morning. 

I did find a bunch of good stuff at the Prestolite website.  A document that pertains directly is a Technical Bulletin on wire size required for various size alternators (http://www.prestolite.com/literature/tech/alts/TSB-1001_wire_size.pdf).  Richard had the size pretty well pegged.

Thanks guys and more input is always welcome.

Jim

[TomC]

With our Freightliner sleeper trucks, they also use remote sensing regulator as described previously.  This way you're getting the voltage of the batteries, not of the entire system.  14.1 volts is where our alternators are set, or 28.2 for a 24v system.  Good Luck, TomC

[Sean]

Jim,

I have a 270-amp alternator (24 volt Delco 50DN), and the ~8' of 2/0 running from it to the chassis batteries melted off its insulation from use, and started corroding.  We just upgraded that run to 4/0.

With ~20' of run at 220 amps, I would run a minimum cable size of 4/0.

FWIW.

-Sean
http://ourodyssey.blogspot.com

[Sojourner]

Voltage output of alternator with the full charge battery to be at least 2.2 voltage higher than 12 volts or 4.4 volts higher than 24 volt at fast idle or higher.  Reading is taken at the alternator outpost. The battery voltage should be nearly the same or no more than a half volt less. This is a factory design spec for all alternator equipped charging systems.

If the voltage reads less than above, with a full state of charge in the battery, then the problem is either too slow rpm or bad diode, or bad internal connection or bad regulator. Bad diode will rob more power from the engine and get hotter than normal plus a louder growling noise. In other words, bench test motor will overload with a bad diode. Oscilloscope test will show one of three sine waves flat or straight with one bad diode.

Here is a link that has a voltage drop calculator at the bottom of the page:
http://www.powerstream.com/Wire_Size.htm

FWIW

Sojourn for Christ,
Jerry

[JohnEd]

Jerry,

That power stream site is excellent.  I book marked that, for sure.

I noticed that there was a caveat on the wire size spec.  It said that the  gauge spec was for wire in free air.  I intend to put my wires in flex conduit and have the conduit imbedded in foam.  I know I will have less cooling than free air.  Your thoughts on wire gauge selection?

Thanks,

John

[donnreeves]

I'm running two 140amp Leese Nevile single wire alternators. One for the house bank the other for chassis. When on the road with one roof air running through the inverter the house alt can't quite keep up with the load. It looses about 5% of the battery charge per hour. I switched from #6 Wire to 00 cable and see no difference. When I switch both battery banks togeather, with both alts charging, both banks stay fully charged. A few people have told me that I can't tie both alts togeather because the regulators would fight each other, but that doesn't seem to happen.   Donn

[rv_safetyman]

As I continue to research this whole alternator issue, I find the Prestolite (Leese Neville) has a pretty good website.  One good document I found it their training manual.  Might be worth a download for some folks.  It should pertain to all starting and charging equipment.  Link is:  http://www.prestolite.com/pgs_training/training_0.php.

Thanks to all who have given me some good information.

Jim

[DrivingMissLazy]

Jerry,

That power stream site is excellent.  I book marked that, for sure.

I noticed that there was a caveat on the wire size spec.  It said that the  gauge spec was for wire in free air.  I intend to put my wires in flex conduit and have the conduit imbedded in foam.  I know I will have less cooling than free air.  Your thoughts on wire gauge selection?

Thanks,

John

John,
My charts show two different tables, one of single conductor in Free Air and one for not more than three conductors in raceway or cable and at different temperature ratings of conductor. Therefore need type of conductor insulation/insulation rating and desired amperage before I can provide you an answer.

Richard

[JohnEd]

Donn,

Your 140 amps "should" be enuf all by it lonesome.  That agrees with your numbers....right?  The reason it isn't working is that your alt isn't keeping the bat voltage at the correct level AT THE BATTERY.  Sorry to shout.

Your LN, as a single wire system, cannot sense the voltage at the battery.  It is at the battery where the rubber meets the road for tricity.  Your alt has two posts, one is ground and the other is B+ or battery positive.  On those two terminals are two wires that come out of the regulator "bump" on the alt.  Remove the connection to the alt B+ and then disconnect the regulator wire.  Attach a wire of like gauge to the reg wire and then run that wire down to your bat + terminal.  When you fire the system compare the bat voltage to before you ran the wire and I think you will see that with the wire connected at the bat the voltage is "higher" at the battery while it is the correct voltage....was that 14.1 for a fully charged bat with the eng at fast idle.   Please make sure.  If it is off by a tenth or two, and it most probably is, adjust the LN alternator.  You do that with a screw driver through the tiny hole in the rear of the alternator and you should get aduj data from the mfr.

This applies to ALL single wire systems.  Most are undercharging the bat because the regulator is "thinking" the voltage at the alt + is the same as the bat....it isn't.  The LN is easy to break out the regulator + wire but they all have that electrical point in them.

The symptom where the single wire alt doesn't charge when the engine first starts but does so after the engine revs is a lead pipe synch symptom that there is a equalizer in the circuit and the alt field is isolated from the bat by diodes and the field can't energize to start things off.  That comes from the horses mouth.

Got more good news for all.  That DN 50 that costs $700 rebuilt with a $350 core can be replaced.  You heard it here first.  Bosh maks a twin 125 amp series connected alternator setup that is belt driven for 24 volts and 250 amps.  Costs?  Really cheap when you consider the DN50 costs and you can put this together yourself for even less.  The two alts weigh less than the 50 so it is cheaper to operate and MPG should increase...theoretically. Not rocket science and really simple after you hear it 'splained".

This was fun!  A lot of people are goingto get a charge out of this.

John

[donnreeves]

John, I already have the wiring in place to do what you sugjest, so that would be easy. What confuses me is the fact that my volt gauges, which are tied to the batteries are reading 14+V with the engine running. Wouldn't that indicate that it's getting full voltage to the batteries? I had attibuted the shortage to losses in wiring and the inverter. Donn