DC power cord

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  #1  
Old 08-27-14, 05:25 PM
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DC power cord

Hello - I'm new here- so I apologize if this is a repeat question, or a no-brain-er but we'll find out...

I am working on an art project in which I want to run 2 old 16mm projectors from a [one] car battery. Both of the projectors have a dial/switch on them which can be turned from A.C ("60 cycle 115 volt") to (DC -or- AC 25 cycle)...
[The way it is labeled is unclear but I cant imagine the "110 volt" applies to the DC option as well]

Other relevant info listed on the projectors:
First one is listed as "AC 115volt -OR- DC 9amp"
Second one lacks that clarification and states "115volt / 8amp"

I've consulted an "electrical specialist" at Lowes who seemed to think that I could cut off the ends of my power chords ["10A, 250 V - 15A, 125V"] and attach alligator clips to connect to the 12V battery.

I would like it to be as easy - but I'm not looking to start a fire-
I did some calculations that seemed to suggest that I would need much heavier wire to make this work.

Whats the truth?
 
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Old 08-27-14, 10:57 PM
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John, your capslock is stuck again.
 
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Old 08-27-14, 11:06 PM
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Wow.. another helpful answer John.

Welcome to the forums sparrow.

It is very doubtful that those projectors would be set up to run on 12vdc.
A make and model of the projector would be real helpful.
A picture of the projector and the power connector might be helpful too.
http://www.doityourself.com/forum/el...-pictures.html
 
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Old 08-27-14, 11:50 PM
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In the early days of power distribution some systems were 110 volts DC touted by Edison and other cities used 110 volts AC that was being pushed by Westinghouse. So they were made to work on either systems.
 
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Old 08-28-14, 05:42 AM
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The projectors each need 9 amps at 120 volts (either AC or DC).

A 12 volt supply would have to deliver 90 amps (into an inverter) for one projector. I suppose that if you were running a special event including a drive in theater out in the field then you might get the projectors running with several 12 volt batteries in parallel but I suspect that a (120 volt AC) generator would be better.

If you used ten 12 volt car batteries in series (now you have a 120 volt supply) then you could plug a projector into a modified extension cord with alligator clips instead of a plug at the other end to clip onto the first and last battery terminals. This may not be used in an area other than a laboratory or electrical equipment room because exposed 120 volts DC terminals pose as much of an electrocution hazard as exposed 120 volts AC.

Generally U.S. 110-120 volt DC equipment of yesteryear used the same plugs and receptacles and lamp sockets as today's 120 volt (AC) equipment.
 

Last edited by AllanJ; 08-28-14 at 06:04 AM.
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Old 08-28-14, 10:47 PM
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Thanks Ray, PJmax, AllanJ for the replies! I've been preparing to hook this thing up, but it sounds like you've saved me from disaster..

I've attached some photos so you can get a better idea of what I'm working with. The projectors are a Bell & Howell 16mm "Filmo Master" and a less common Bell & Howell "time & motion study." They are variations of more or less the same machine (model 173). In the photos you can see that I have made modifications to fit them into the headlight cavity of my van (as seen in 3rd photo).

They definitely are from yesteryear - 40's or 50's at least - so this 11O V DC is starting to sound most plausible.

Allan- I hear you with the series of 12v batteries that compile into 110v. I've looked into this a bit, but for my purposes I need to keep the whole system as compact as possible, so I wasn't too keen on it. However, the suggestion does begin to clarify why this wont work as I hoped.

My previous calculation (using online calculator) was that if @ 120 v & 20 amp (total) I am drawing 2400 watts, then with a 12v batter at 2400 watts, I would need a wire that could handle 200 amps. Perhaps it doesn't quite work that way?


My next question, then, is about power inverters. This was the original solution I found and I can happily run one of these projectors through the 2000 watt inverter that I have. When I plug two of them in, neither will run. What I have figured is that I will need a 2500 watt inverter at the least... is there any reason why I would actually need something more substantial?

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Old 09-01-14, 06:56 AM
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When the projector starts up it may draw somewhat more than its running amperes/watts for a moment. For example 9 amps at 120 volts is 1080 watts running but the projector might draw something like 1500 watts for a moment. An ordinary circuit breaker or fuse might not trip on such a momentary overload but an inverter might trip its internal breaker.

Also, is your 2000 watt inverter able to supply 2000 watts continuously or only for occasional momentary peaks?

The AC output from the inverter needs wires that handle 9 or so amperes (14 gauge minimum for typical household grade circuits and receptacles).

The DC line from battery to inverter input needs to handle 200 or so amps depending on the power needed to achieve the needed 120 volt output. Chances are you will need two inverters, one for each projector, with 90 amps of DC into each. I think this would mean #2 gauge copper wires. Keep the distance short, say less than 20 feet and you would not have to de-rate (and use larger wire) to account for the 150 amp or so startup draw and the resulting voltage drop.
 
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Old 09-01-14, 11:58 AM
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I have made modifications to fit them into the headlight cavity of my van (as seen in 3rd photo)
In your van


With a +2000 watt inverter you would need better than #2 wiring and a second battery.
 
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Old 09-01-14, 12:09 PM
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What!? Are you going to use them for headlights? If they are in a van why not install an RV type generator?
 
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Old 09-01-14, 12:56 PM
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If driven on a public road a cars headlights must meet federal guidelines. I doubt movie projectors qualify.
 
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