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Onan Generators

What Have You Done to Your Onan Generator Today?


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  #111  
Old 02-17-2013, 12:35:10 PM
Leon N. Leon N. is offline
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Default Re: What have you done to your Onan generator today?

ETN550: Nice to hear from you. I am impressed with what I see. Your battery arrangement caught my eye because I have Onan Tech bulletins and major service manuals which state the following with respect to battery requirements. I assume your DJA uses exciter cranking and does nt have a seperate starting motor. If that is the case, then Onan says the following:

"Exciter cranked plants use two six-volt batteries in series. Each battery must be at least 105 amp. hour capacity. Do not use undersized batteries on revolving armature plants as serious armature damage may occur."

That is why I turned down a chance to purchase an old exciter cranked J series plant after the seller said he could not get it started and the battery went dead.

Leon

I trust you know this. The only problem I see if you use two 12-volt batteies in parallel is in the way you recharge them or keep them on float charge.
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  #112  
Old 02-17-2013, 01:01:36 PM
rmchambers rmchambers is offline
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Default Re: What have you done to your Onan generator today?

I'm not sure if that recommendation was for batteries that may have been somewhat depleted. My MDJA 3.0 gets spun up fast with a single12V battery I also have thick short cables as well. The key here is having a working decompressor solenoid. Once the engine steel and copper and cast iron flywheels get spinning the solenoid lets the exhaust valve close and there's plenty of inertia to get the engine to pop off. Extended cranking (because of fuel issues etc) is going to kill your exciter real fast. If you've run your machine dry, open up the nut at the injector and bleed the air out properly, if you keep trying to crank it to make it work you're going to let the smoke out, but that's probably true for any Diesel engine. At least though if you have a starter motor that's an easy swap-out.. the exciter cranked ones - not so much.
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  #113  
Old 02-17-2013, 07:21:53 PM
DrCharles DrCharles is offline
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Default Re: What have you done to your Onan generator today?

A 12 volt, 105 AH battery (or two 6 volts, etc) is a huge hunk of lead and it may well not be necessary, because the amp-hours is not the "real" reason for that spec.
I can't find the specific Onan manual I read this in, but I recall that there must be at least 10 volts at the solenoid terminal during cranking. A smaller battery should do just as well as the two 6 volt 105 AH recommended many years ago, providing that it has sufficient cranking and cold-cranking amps to meet that voltage requirement!
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  #114  
Old 02-17-2013, 08:21:11 PM
Leon N. Leon N. is offline
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Default Re: What have you done to your Onan generator today?

I new this would start a controversy. Oh boy! Dr. Charles, I have a lot of respect and admiration for those early on Onan design engineers. I might refer you to , for example, one of the Onan major service manuals, #967-500, page 39. I might add, that any low duty cycle DC motor that has a commutator and the rotor is locked puts much stress on the commutator. If there is insufficient torque generated to turn the rotor, over heating may develop very quickly. Exciter cranking circuits are designed for short operation and with insufficient amperes to generate the necessary torque damage may ensue.

Six volt batteries are designed with 3 banks of 2 volt lead acid cells connected in series, thus 6 volts. Each 2 bank consists of many more 2 volt cells connected in parallel than you will find in a 12 volt battery. Thus you can get more amperage out of a 6 volt battery? Maybe that is why exciter cranking has limited utility. However, exciter cranking was dictated in part by the cck designed generator.

Sure you can probably use a small 12 volt batter to start a CCK if optimum conditions exist. If it was me, I would not risk it, especially if the 12 volt is not kept on float charge.
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  #115  
Old 02-17-2013, 09:21:30 PM
DrCharles DrCharles is offline
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Default Re: What have you done to your Onan generator today?

6 volt batteries have twice the amperage because they have half the voltage of a 12 volt battery. In the same physical sized case, naturally there are twice as many 2 volt cells in parallel. The number of watt-hours per pound remains the same!

If you put two 6-volt batteries in series, of course you get 12 volts at twice the amperage of a single 12 volt battery of the same case size, because now you have twice as big a battery. The same is true if you put two 12-volt batteries in parallel. Twice the lead, twice the WATT hours (volts * amps * hours).

I never said that insufficient battery size would not be harmful to the segment through which all the current is flowing (not turning the armature). Obviously it is. And the need for keeping your batteries at 100% charge (by float charge) is also the same regardless of the ultimate number of series/parallel plates.

There are some pretty hefty 6 volt batteries available at your local farm store. But again I recommend checking the cranking amps, which is much more important than the amp-hours, especially since as you point out the duration of operation should be kept very short. Some of the larger, heavier batteries (more amp hours) actually have FEWER cranking amps than the smaller ones!

So if it makes you feel better to have two 6-volt 105AH batteries in series, rather than two 12-volt 50AH batteries in parallel, go for it! As long as it turns over smartly.
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  #116  
Old 02-17-2013, 09:47:46 PM
ETN550 ETN550 is offline
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Default Re: What have you done to your Onan generator today?

My batteries are actually group 27 deep cycle. They are 650 cold cranking amps each. So unless I'm mistaken, in parallel they should be good for 1300 CCA at 12 volts. However, my jumper wires between the batteries are 2Ga, not 00. The wires to the gen are 00. The Onan DJA manual says to use (2) Group 1H 6 volt batteries in series with 450 CCA. So, unless I'm mistaken (2) 6 volts in series at 450 CCA would be 12volts, 450 CCA. So even though my jumpers are undersized just one of my 27's would be enough. I'll put a meter on it next time I crank to see what the voltage is at the start solenoid in the box.

Good point about not sitting on one comutator contact and not spinning. I'll always remember that anytime I start it and quit cranking immeadiately if it does not spin right away.

Great info, and good discussion. The armature and the decompression solenoid are two unobtanium items I do not want to jepardize!
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  #117  
Old 02-17-2013, 09:52:46 PM
Leon N. Leon N. is offline
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Default Re: What have you done to your Onan generator today?

Re your comment: "---If you put two 6-volt batteries in series, of course you get 12 volts at twice the amperage of a single 12 volt battery of the same case size---" Strictly speaking you get more endurance or amp hour capabiity not more amperage. The former is what is important for exciter cranking.

Also, the comment: "---As long as it turns over smartly. ---" Obviously is subjective. Unless one knows more than the designers, I would opt to go by what they recommend.

I do not think the term CCA was around in the 50's and 60's, but the term amp hour was and remains valid today.

You would get more amperage if you put two 12 volt batteries in parallel, but that is ill advised because the two batteries will not share the load equally, especially as they age and striation comes into play. Also it is more difficult to float charge two 12 volt batteries in parallel because their internal resistances will eventually deviate making an equalization charge necessary. That is bad enough with a single 12 volt battery or two 6 volt jobs in series. So why complicate things. Follow the Onan specs and you will minimize your problems.
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  #118  
Old 02-17-2013, 10:05:20 PM
DrCharles DrCharles is offline
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Default Re: What have you done to your Onan generator today?

Deep cycle batteries in a given case size have fewer cranking amps than starting batteries. That's the tradeoff for being able to discharge further without damaging the plates (lots of info at batteryuniversity.com and other sources).

Remember that the CCA rating is at 0F, for 30 seconds, sustaining a minimum of 1.2 volts per cell (that's only 7.2 volts for a 12 volt battery, and at the terminals!) I'm not sure how to directly translate that to 10 volts minimum (1.66 volts per cell), but obviously more CCA is better.

Unless your inter-battery cables are very short, I recommend you use heavier ones...

Quote:
Originally Posted by Leon N. View Post
Re your comment: "---If you put two 6-volt batteries in series, of course you get 12 volts at twice the amperage of a single 12 volt battery of the same case size---" Strictly speaking you get more endurance or amp hour capabiity not more amperage. The former is what is important for exciter cranking.
I disagree. You need all the amps you can get, but for a very short time. There will always be plenty of amp hours.

Quote:
Also, the comment: "---As long as it turns over smartly. ---" Obviously is subjective. Unless one knows more than the designers, I would opt to go by what they recommend.
Those designers were recommending what was available 40 or even more years ago. Batteries have improved since then.

Quote:
I do not think the term CCA was around in the 50's and 60's, but the term amp hour was and remains valid today.
It wasn't. The point is not whether the term "amp hour" is valid, but as I have already pointed out at least once, it is NOT directly related to cranking amps!! Smaller amp hour batteries often have MORE cranking amps than bigger ones. Look at the stickers on the batteries at the farm store the next time you visit.

Quote:
You would get more amperage if you put two 12 volt batteries in parallel, but that is ill advised because the two batteries will not share the load equally, especially as they age and striation comes into play.
And what about the two 6-volts in series... why would you think that six 2-volt cells (in two separate boxes of three separate compartments each) series is any more or less difficult to equalize than six 2-volt cells (in one box with six separate compartments)??

I'm done with this discussion. Do whatever makes you feel better.
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  #119  
Old 02-18-2013, 11:16:36 AM
Leon N. Leon N. is offline
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Default Re: What have you done to your Onan generator today?

Not to continue the discussion but for ETN550's sake, note that almost any 12 volt battery will initially supply the required amperage. It is simply Ohms Law that the amps equates to the voltage divided by the resistance. The point I was trying to emphasize, and you hit upon it by stating the Onan manual requirements is that you need a 12 volt battery source that has the endurance. Endurance meaning to be able to supply 12 volts for however long the exciter cranking cycle has to run. Obviously Onan built in a safety margin when stating the requirement. Just as important is the cabling and the cable lugs and cleanliness and tightness of the connections to minimize voltage drops. I am sure the Onan manuals cover all this.

Today, there are many 12 volt batteries that will meet the Onan requirements. If I were you, and reliability is important, I would use 2 new six volt batteries which meets the Onan specified requirements and install a temperature compensated float charger to maintain the batteries in top condition. That will minimize battery sulfation over time. For example, I can take a worn out 5 year old automobile battery and by keeping it on float charge get another 6 years of use on my JB. Your battery requirements are more severe, but with new batteries, and on the proper float charge regime, you should be able to easily get a dozen years of use.
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  #120  
Old 02-18-2013, 02:41:16 PM
len k len k is offline
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Default Re: What have you done to your Onan generator today?

I'm no expert, but I suspect the issue here is: years ago bats may not have had group size or CCA ratings. Amp-hr rating may have been all there was to specifiy how big of a battery to use. And it was assuemed you would use a "starting" bat and not a "deep-cycle" bat.

For a given physical size of bat, a "starting" bat had many more thin internal plates (~twice as many). For lots of surface area, so it could produce lots of amps, (but not for hours).
And a "deep-cycle" bat had fewer thick plates, so it could produce a lower amount of amps for a long time (hours) without fully consuming/disolving the internal plate. For uses like boat lighting.


For a given amp-hr bat, a deep cycle bat can't produce as may starting amps as a stating bat, so using amp-hrs to "size" it is really not a proper way to spec a bat. I believe these days Onan engineers would specify CCA not amp-hrs.

(I've been told they may not list bats as starting or deep-cycle anymore.)
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