Meaning of Electrical Rating

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PaulHand

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I am working on installing an oxygen concentrator and a nebulizer in the back of my pickup truck for my disabled wife. I am trying to figure out the additional amp output needed from an alternator to support the additional load. The concentrator's 120V rating is 4.3 amps/390 Watts; the nebulizer is 1.6 amps/98 Watts.

I don't understand what these ratings mean? If I divide 390 watts by 120 volts I get only 3.3 amps which is significantly lower than the rated 4.3 amps. So what is the amperage required by the device?

The relationship between the amps and watts ratings is not consistent between the concentrator and the nebulizer?

Thanks from a non-technical newbie
 
Re: Meaning of Electrical Rating

I wish I could help you with your questions for your wife's needs but unfornately the forum doesn't allow us to assist those who aren't in the electrical field.
 
Re: Meaning of Electrical Rating

He's sorta talking automotive though. I think that's okay?

Be safe, get a 1000 watt DC/AC converter. :)

Just don't ask us how to wire your house. ;)
 
Re: Meaning of Electrical Rating

Paul
You need to contact the manufacture of the health equipment. Most inverters only put out about 110 volts and it is in a square wave form which drops the available voltage. some equipment can not run on this type of power and can be damaged from it. Triplett does manufacture true sinusoidal inverters and would be safe to run on but I would check with the manufacture first. I would also plain on installing extra battery's also as @ 12 volts these inverters can draw about 83 amps @ 1kw which would run a regular car battery down in minutes. So plain on back up if you ever have a break down.

[ May 17, 2005, 08:16 PM: Message edited by: hurk27 ]
 
Re: Meaning of Electrical Rating

Well, it's an inverter and you'll need to provide just under 500 watts so I would say a 600 watt inverter would be minimum.

They start getting expensive when you start adding more 100's of watts.

But you don't want the thing to be overloaded and "turn itself off".

You really should talk to someone who deals with these for medical equipment.

Wayne's pretty knowledgeable about inverters. Maybe he's around.

Edit: The 500 watts for the equipment will draw 42 more amps from your alternator. Plus a couple extra amps that will be lost in heat.

[ May 17, 2005, 08:46 PM: Message edited by: physis ]
 
Re: Meaning of Electrical Rating

Wayne is around, hi Wayne.

Edit: I thought they made triangles.

[ May 17, 2005, 08:23 PM: Message edited by: physis ]
 
Re: Meaning of Electrical Rating

Manufacturers are free to describe the ratings of their equipment in any (?truthful?)way they wish. But it is not always done in clear terms.

You are correct in thinking that you should be able to divide the power drawn by a load (in units of Watts) by the supply voltage (in units of Volts), and get the corresponding current (in units of Amps). But you should not presume that the rated current and the rated power, as stated in the manufacturer?s literature, are based on the same conditions. The two ratings may not correspond to each other, because the may have been derived by different methods.

My guess is that the current rating is based on the initial, higher current draw that the machine requires, when you first turn it on. My other guess is that the power rating is based on the maximum power that the machine will require, when it is running at its full capacity. In other words, I am guessing that the Oxygen Concentrator draws 4.3 amps (corresponding to 516 watts) when you first turn it on, and settles back to a 3.3 amp draw (corresponding to 390 watts) during its normal running operation. Similarly, I am guessing that the Nebulizer draws 1.6 amps (corresponding to 192 watts) when you first turn it on, and settles back to a 0.8 amp draw (corresponding to 98 watts) during its normal running operation.

My guess may be way out of line, but it seems reasonable to me. From that set of ?guesses,? I think that your alternator should be able to handle the starting conditions of 516 plus 192, or a minimum of about 700 watts. I have no clue as to whether any automotive shop has an alternator that you can retrofit into your truck, and that can supply that amount of power continuously.

Please accept my best wishes for success with your project.
 
Re: Meaning of Electrical Rating

You are pretty much correct Charlie.

I actually missed how much the peak is going to be. But it's of such a short duration that:

[1] The inverter can handle it. But that needs to be varified. They have a peak rating in addition to constant.

[2] The batteries are going to absorb the peak draw on the alternator. If they're to low you're gonna be all but out of luck anyway.

There are larger alternators for just about any vehicle.

And Paul, appearantly you have the acceptance of the moderators. :)

Edit: This is what I suggest is required:

A 600 watt inverter.
An alternater capable of another 50 amps above what the vehicle needs.
A backup or isolated battery system.

[ May 18, 2005, 12:02 PM: Message edited by: physis ]
 
Re: Meaning of Electrical Rating

Is it possible that these units have motors and the power factor is not 1? That could explain why watts is not equal to volts * amps.
 
Re: Meaning of Electrical Rating

I don't know what type of truck or size alternator you have. From the late 80's most have around a 100 amp rated alternator. A good one will put out more at cruise speed. A alternator will not last long running at max. They will get too hot. The stock harness is undersized for the alternator output many times with a #12 wire. If you turn everything on (lights, max A/C, wippers, brake, radio) the alt will be putting out 60-70 amps. Also if overloaded the voltage drops below 13.3v (some cars run like poop at that point).

Many trucks have aftermarket high output alternators available. You may want to consult an auto shop that is good with custom electrical.

Tom
 
Re: Meaning of Electrical Rating

Paul, I apolagize. I didn't pay enough attention to your first post.

I have to agree with Charlie that the system should be built to handle the maximum demand and I didn't correctly incoreprate the peak draw.

Without redoing Charlies math and using the 700 watts that would put about 60 more amps on your alternator.
 
Re: Meaning of Electrical Rating

I have two custom built alt's on my work van each @ 180 amps with the rpm's of my motor being around 1200. At idle they put out about 140 amp's each. I have 4 inverters feeding off 5 deep cycle marine battery's that get replenished by a electronic voltage regulator that maintains the charge rate the deep cycles get. A must to intermix deep cycle and car batteries. A car alt try's to deliver about 14.2 volts at what ever amprage it can deliver, this will destroy a deep cycle battery. A deep cycle battery should be maintained at about 13.4 to 13.6 volts at no more than 10 amps other wise you just over heat the plates. By using hi current diodes between each battery and supply and loads you can isolate the two systems to make them all work together.

Try calling any starter/alternator rebuilding shop's and ask if they can over size your alt's or supply you with ones that can be over sized.

As with any electrical system I must insist upon fuse links at each source of power (battery's, Alt's Etc...) and fuses at each sub systems connection point to source!!! Just because it's only a 12 volt system doesn't mean it's not dangerous. Low voltage can and will cause a fire as the amperage is much higher and wire sizes will have to be much larger. Connections have to be good and tight and clean with a good di-electric grease applied. otherwise the system will be only as good as the weakest link or connection!
If you don't understand these dangers or this type of system. THEN GET SOMEONE WITH VARIFYBLE KNOWLEDGE TO HELP YOU!!! We had three teens killed here because they installed some high powered audio equipment and didn't think they needed to install any fuses. they were going down the expressway when the wires feeding the battery in the trunk shorted and caused that battery to explode bursting the gas tank. So take heed to this warning.
 
Re: Meaning of Electrical Rating

I haven't read all of your post Wayne, I will, but why custom build an alternator? As far as I know these are off the shelf items in a lot of different output ranges anymore.
 
Re: Meaning of Electrical Rating

Have you ever looked under the hood of a "96" GMC van lately? yes there are many alternators out there but try to get one to fit? Luckily for the motor I've got with air power steering, and all the other junk under there they did have two places they installed the alternators on them so a trip to a junkyard resulted in finding brackets to fit another alt on the other side of the engine. But space was limited so I was stuck with only a few alternators that would even fit in these spaces. I have a rebuild shop close to ours and he was able to modify my alts with heaver windings and electronics allot cheaper than one of those off the shelf alts. Plus he installed everything new in it. so far they have lasted 3 years. And they still show around 14.2 volts @ 360 amps on the digital amp meter when they are in full recharge with the inverters loaded. which is when the engine automatically starts @ 11.5 volts via the Bulldog autostart System.
 
Re: Meaning of Electrical Rating

Ok I've had a chance to read your post Wayne.

All very good and pertinant information. I was going to ask about deep cycle versus standard lead acid and you covered that somewhat. My feelings on the two is that I like the standard lead acid because they charge so much faster and are more rugged in general. Deep cycles take a very long time to charge. more than a day is common. The only real up side is that you can operate from them a lot longer, but my opinion is that it's best to use the charging system rather than the batteries for typical operation.

You're absolutely right about being aware of potential problems. It is very important to realize how much damage can be done if the battery system gets shorted. Literally gobbs of current will be spent very rapidly. Hundreds of amps. It might actually be fortunate (well, sort of) if a battery explodes cutting the circuit.

I used to use a self reseting circuit breaker at a lower amperage, where I wanted the system to operate, and a higher amperage fuse for actual protection.

As far as alternators, I don't mean to argue with you Wayne, if you can have them custom built at a reasonable price that's fabulous. I was just saying that I've always been able to buy whatever it was I needed. It's been at least 10 years though for me.

I've always built my own diode/heat sink assy's. Big, bulky solid. They have these like 5 ounce isolators you can get at car parts stores. I've never used them and don't know what they are or how they work.
 
Re: Meaning of Electrical Rating

I had no idea I would get such an interested and kind-hearted response. Thanks to all of you. My wife?s lungs have very low capacity and the continuous flow oxygen supplied by the concentrator is much better for her than the puff oxygen supplied by the regulator attached to an oxygen tank. We are not wealthy, but cost is outweighed by other considerations.

About 6 years ago, we installed the first concentrator/nebulizer system in our 1996 Chevy truck. My son has a small fleet of trucks, and his mechanic installed the system. The mechanic is very conscientious, treats us like family, has considerable practical experience and almost no formal training. On the first system, the only thing I did was to research on the Internet about what inverter to use. I came with the Exeltech true sin-wave inverter, and we bought their highest power device, 1100 watts/2200 surge, the Exeltech XP1100 12V.

On the first system the mechanic left the standard alternator in place, and added a standard car battery connected to the inverter. He installed an isolator, which was supposed to separate the concentrator system from the truck starting system. We measured the concentrator, and its start-up draw is about 2 ? times its running draw. I suspect the nebulizer is about the same --- both are compressor-centered devices. This system was somewhat experimental; we wanted to find out if we could get something to work.

We have had at least two experiences with both batteries going dead. The alternator failed, and the local GM dealer replaced the 100 amp alternator with a 140 amp version. The original car type battery failed and we replaced it with a deep cycle D34 Optima. We have had two Optimas, each lasting about 2 years. The present configuration has worked quite well except for the short life of the Optimas. It has been very dependable once we made the alternator/battery upgrade.

In April 2004 I bought a new Chevrolet truck and want to set it up with a concentrator and nebulizer. This truck is still under an extended warranty. I intend to keep the old truck with its concentrator system as backup, but will be more comfortable with a newer vehicle as our main transportation. I have tried everywhere that I can think of to get someone with more training to do this work, and have ended up again with my son?s mechanic. No one could be more conscientious, or care more about us. The local GM dealer has also done his best to find an installer without success. We are in a small town in Southern Arizona, with the closest city being Tucson, 125 miles away. I am willing to take the truck to Tucson, but have found no one more qualified there either.

On the new system, in order to provide more emergency protection as well as better battery life, we have had a suggestion to use two deep cycle batteries in parallel. We have ordered two Optima D31As, each rated at 75 Amp Hours versus the 55 AH of the D34. We have purchased another Exeltech 1100. We have a new concentrator rated at 4.3 amps versus the old concentrator?s 5 amps. The new truck presently has a 105 amp stock alternator. GM has a 145 amp version which is used on 4 wheel drive versions of our truck and the GM rep our dealer has contacted feels this would be enough increase in output, and would be certain not to damage the truck?s electrical system. I think it is likely that the 2004 truck has much more delicate electronics than the 1996.

Thanks again to everyone for your interest and help.
 
Re: Meaning of Electrical Rating

I should have pointed out in my last message that it was after completing the actions described there that we came to the question of what alternator to use, which gave rise to the question I posted to this forum about what the equipment name plates mean.

My previous message was intended to provide more information about the problem. Although the GM person recommends 145 amps, other advice is for the alternator to be at least 160 amps, and all the way up to 220 amps.
 
Re: Meaning of Electrical Rating

"The alternator failed, and the local GM dealer replaced the 100 amp alternator"

Like I said a stock 100 amp alternator is not good for much more than orignal equipment only.

Your adding a lot of amps load. Plus your inverders have a loss. All the batteries suck a lot of power. To recharge a battery can draw 20-30 amps each. Maintaining the battery charge can draw some power too. I would go with a 200 amp alt for it. You could find one on the net probibly cheaper than the GM 145 amp. Look here:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7955200606&category=33573&sspagename=WD1V

200 amp with 125 amp at idle to fit your PU for $229. I'm not recomending this place just saying look around and you will find what you need for a fair price.

The electronics are not any more senitive in the 2004 than the 1996. If anything maybe GM got their act together and made them more durable. ECM used to be junk in every GM.

Tom
 
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