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Eastern Railroad Discussion > 74 Volt Inverter Question


Date: 07/20/03 16:00
74 Volt Inverter Question
Author: mttrainman

Does anyone out there know where to find or how to make an ?inverter? that will turn the 74 V (I forget if it is AC or DC) available in the cab on most locos,into either proper house-hold current or even 12V as available in an auto? I can guess why the railroads probably dont\' want us to have this but it can\'t hurt to have when stuck on a lonely siding for multiple hours. (Portability is a key factor, also!) Any suggestions would be greatly appreciated!

MT



Date: 07/20/03 17:41
Re: 74 Volt Inverter Question
Author: apteryx

It\'s important to find out if the 74V is AC or DC. If it\'s AC you won\'t need an inverter; just a transformer for an AC output or a transformer and rectifier for a DC output. If the 74V is DC then you can use an inverter to get AC (although it\'s not one of the more common DC input options) or a DC-DC converter for the 12V DC.

What are you trying to run with it?



Date: 07/20/03 17:50
Re: 74 Volt Inverter Question
Author: run8

It\'s 74V DC.

There are commercially made inverters to give 110VAC, but they are very expensive, like in excess of $1,000. That\'s what the railroad buys to power things like AC fridges and microwave ovens.

If you can get hold of an old locomotive radio, the radio itself is powered by 12VDC, and there is a converter in the box to drop the 74VDC locomotive power to 12VDC.

Otherwise, if you only want to use something that doesn\'t take to much power, you could probably make a circuit to provide 12V for less than $100. Have any friends who are good at electronics?



Date: 07/20/03 18:02
Re: 74 Volt Inverter Question
Author: del

First of all it is 74 VDC. What are you going to use the power for? Something like a coffee pot that is suppose to run on 110 VAC will work just fine on 74 VDC. Many of the refrigerators on the locomotive run on 110 VAC and there is an inverter on the locomotive to supply that. I caution though not all refrigerators run on 110 VAC. It is much easier to drop the voltage to 12 VDC than invert to 110. All you need is a variable resistor. That is how they dim the headlights on a locomotive, they put a resistor in the circuit and lower the voltage.



Date: 07/20/03 18:38
Re: 74 Volt Inverter Question
Author: mttrainman

Thanks all for the replies! Although this sounds like a pretty expensive proposition ($500-$1000!!), I am still very interested and would like to hear from others as well. I am curious if I could run a standard house-hold fan off of the 74V dc. I am very hesitant to try this on my own without more knowledge so more input on this topic would be appreciated. Thanks again.

MT



Date: 07/20/03 19:08
Re: 74 Volt Inverter Question
Author: del

A household fan would have an AC electric motor, it would not work on DC. You would get smoke and fire. It would work in the electrical socket the refrigerator was plugged into if it is an 110 VAC refrigerator.



Date: 07/20/03 19:43
Re: 74 Volt Inverter Question
Author: BaltoJoey

I bought a power inverter at Sam\'s Club. I can either plug it into my cigarette lighter and it also has clips for the battery terminals. In fact most of your auto stores sell them now. Also, go to one of the chain stores, WalMart, Sears, Target. They sell them there.



Date: 07/20/03 20:00
Re: 74 Volt Inverter Question
Author: del

Unfortunately if you hook your Sam\'s inverter designed for a 12 VDC input to 74VDC if it didn\'t blow up it would put out 700 VDC.



Date: 07/20/03 21:05
Re: 74 Volt Inverter Question
Author: sdp40f-500

Hi. I bought a pair of ditch lights from a rail scrapper and they needed 74 VDC, so I just visited an old electronic store and they had a variac, which is a variable output, high amp device made to work with 120 volts a/c input and then I just added a recifier to change the output from alerating current A/C, to direct currect DC and I had a source to power the lights up to 16 amps and I had less than $70.00 tied up. The ditch light at 74 Vdc only pulled about 11 amps. I could plug into any 120 volt outlet and use the light anywhere and I could run them down dim and anywhere in between up the max 74 VDC. Very bright and very cool toys. Davedel wrote:

> Unfortunately if you hook your Sam\'s inverter designed for a
> 12 VDC input to 74VDC if it didn\'t blow up it would put out 700
> VDC.
>
> [%sig%]



Date: 07/20/03 21:35
Re: 74 Volt Inverter Question
Author: Vunderbob

A variac is a transformer, and if you plug in to DC, it\'s a short circuit.

If you want to run a fan, try to find an old one with a universal motor. It won\'t care if you feed it AC or DC. However, 74 volts might be a bit anemic.

My other suggestion is to find a battery operated fan (DC), and have someone cobble up a DC-DC converter to run it...



Date: 07/21/03 03:37
Re: 74 Volt Inverter Question
Author: android

Vunderbob wrote:

> My other suggestion is to find a battery operated fan (DC),
> and have someone cobble up a DC-DC converter to run it...

One thing about DC-DC converters is heat. If you drop from 74V to 12V, you are basically "burning" up the 62V in between, which would create quite a bit of heat. I remember the Volt-A-Drops that used to be sold for to drop 12VDC to 6VDC or from 24VDC to 12VDC, many of these were crude, you had to use a load in a certain resistance range to actually get the intended voltage. If you were to build a voltage dropper from 74V to 12V, it would get hot, and you\'d have to overbuild it intentionally to protect the chips from burning out. Then again, I suppose you could build an electronic converter of some kind, a rough dc-ac converter, run that through a step-down transformer, then take that and run it back to DC, but I doubt you\'d be able to get more than couple of amps available. ALSO, anything you\'d build with electronics would have to have all sorts of filters to protect from spikes and surges... I\'m sure you\'ve seen how the headlights change brightness at times..



Date: 07/21/03 06:13
Re: 74 Volt Inverter Question
Author: k-5

mttrainman

email me off list at nathank5h@yahoo.com

I can help you.


K-5



Date: 07/21/03 12:39
Re: 74 Volt Inverter Question
Author: BaltoJoey

Ooops, I misread the question. Please disregard my previous post. Mea culpa, mea culpa, mea maxima culpa !!

BaltoJoey<----face as red as a tomato



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