Using 12v Viair Compressor with 24v Pinz

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Hersir
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Using 12v Viair Compressor with 24v Pinz

Post by Hersir »

I've been shopping for one of the Viair portable compressors. While they make 24v systems for on-board air (OBA), all of their portable systems are 12v. I know very little about electrical systems. As I understand it, however, the 24v Pinzgauer uses two 12v batteries in series (that is, two 12v batteries work together to make 24v for the truck by being connected to each other). If I were to open the battery box to attach the cables for the portable compressor I would presumably attach the positive clip to a positive terminal on one battery and the negative clip to the negative terminal on the same battery.

Do I need to detach the other battery to do this or do anything else so as not to put 24v to my 12v portable compressor?

Sorry for such an elemental question. I'm sure this is pretty basic but I don't want to fry the compressor or damage the truck's electrical system.

Thanks.
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Post by Jim LaGuardia »

When tapping 12v from the batteries, you must connect only to the battery with the ground strap
One other warning, using a 12v tap requires caution when starting, if battery key is off and starter button pushed, the starter load will go through the item (ground path)and let the smoke out of the 12v accessory :shock:
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Post by Hersir »

Thank you Jim.

One more question, would you recommend I have the vehicle running before attaching the compressor's cables to the battery with the grounding strap--or should the vehicle be off when using the compressor?

As I understand your warning, I should not attempt to start the vehicle when the compressor is attached so as not to send a 24v load to the 12v compressor.

Thanks again.
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Post by Jim LaGuardia »

It can be operated with engine running.
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Jimm391730
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Post by Jimm391730 »

Most of these high performance compressors draw alot of current, so whichever battery you connect to will be drained down less than the other battery. Since the Pinz system charges them both equally (since the same charging current flows through both batteries in series) the unused battery will get overcharged and the used battery will not get charged fully. Both of these cases shorten the battery life if the batteries are not equalized by independent charging with a quality 12V battery charger. Battery life could be just a few months if you use the compressor often.

Charge equalizers will be of value with this senario as they will take charge from the unused battery and add it to the used battery, equalizing the charge of both so the truck's charging system will charge them equally.

Jim L. is right to say that you would probably want the engine running as some of the high performance compressors can draw 50-80 amps, and having the alternator supplying as much as 30 amps will help keep the battery from discharging as quickly.

But if you connect the compressor directly to the battery terminals through the open battery door then no damage will be done to the truck or compressor as long as the compressor is not grounded to the truck; but due to the current draw you would not want to start the truck with the compressor running, anyway.

If you use the compressor for half your tires when powered from one battery and the rest when connected to the other battery (trying to get equal use from each battery) and occasionally independantly charge each battery (when home, every 3-6 months or so) then you would probably not have much degradation in battery life.

So using one battery to power your compressor can ruin batteries if not done properly, but it can be done in an OK fashion with a little care and concern.

Best of luck,

Jim M.
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Post by ABSOLUTSECURITY »

Why dont people just stay pure and buy 24 volt stuff??????????????
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Post by M Wehrman »

$$$$$$$ :lol:
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Post by ABSOLUTSECURITY »

What are $$$$$$$$$$$$$ 's LOL!!!!!!
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Post by Fleg »

Jim LaGuardia wrote:When tapping 12v from the batteries, you must connect only to the battery with the ground strap

Why?
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Post by undysworld »

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Last edited by undysworld on Thu Oct 14, 2010 8:08 am, edited 1 time in total.
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Post by Fleg »

undysworld wrote:I think Jim's assuming that the compressor negative gets chassis grounded, so if you hook the positive to one batt. you get 12v, and if you hook to the other it would be 24v. Otherwise, if you hook directly (+ & -) to the first batt. (the one which - does not go to chassis ground), and accidentally touch the compressor to the chassis ground, you've got an electrical disparity (sparks) there.

I think this is what Jim L. wrote about, and why Jim M. wrote that, done carefully, it's ok. (Correct me if I'm wrong guys.)

Paul
If you are using the chassis for the ground then you do have to connect to the first battery in the series but if you are connecting both leads directly to the battery then it shouldn't matter.
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Post by undysworld »

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Fleg
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Post by Fleg »

undysworld wrote:This thread is rapidly getting confusing without pictures. As I understand it:

Even if you hook direct to the battery (both + and - terminals) using the battery who's "-" terminal is at the battery-to-battery connection (as opposed to the battery who's "-" terminal goes to chassis ground), then the "ground" of the compressor will still be at a 12v disparity from the truck's chassis ground. If you touch then that compressor to the truck chassis, you could have problems, as you may have effectively grounded the + of the opposite battery.

Done really carefully, this should work, but done haphazardly, the results could be substantial. (Kids, don't try this at home!)
Lets start fresh;

If you are connecting directly to the 12V batteries, both negative and positive terminal, then you can connect to either battery that you want and get 12V.

If you are connecting only the positive wire to the battery and the negative wire to chassis ground then you must connect to the battery that has the ground strap to it to get 12V. Connecting to the positive (+) of the other series battery will give you 24V.

The best way to solve the issue is to get a 24V compressor. I just picked up a 450C 24V compressor that is their top of the line industrial compressor for $244 delivered. 100% duty cycle, almost 2CFM at 0psi. SUpposed to be able to fill up a tire in under a min. I'll have a writeup on a OBA setup on my webpage soon.
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Post by undysworld »

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Last edited by undysworld on Thu Oct 14, 2010 8:09 am, edited 1 time in total.
Fleg
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Post by Fleg »

undysworld wrote: True, EXCEPT. What I'm trying to warn folks about is that if you do this, and you hook to the battery which is not chassis grounded, an electrical disparity will exist between the compressor ground and the truck's ground. This means that if you then touch that compressor to the truck's chassis, sparks will fly, just as if you'd grounded a normal 12v battery.
Incorrect, you'll get 24v at the motor and that is only if that compressor motor is case grounded. Many of the good ones are not. The only sparks that could fly is the result of doubling the voltage that the motor is designed to operate at.

In reality you're not supposed to be doing any of this anyway. Connecting to only one of a series battery setup degrades that battery more then the other that in turn over charges the other battery and damages it as well. Again, the best bet is to get a 24v compressor.
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