Film-Tech Forum ARCHIVE: Where Are They Now (Drive-In Heater)

This is topic Where Are They Now (Drive-In Heater) in forum Ground Level at Film-Tech Forum ARCHIVE.

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Posted by Steve Anderson (Member # 364) on 09-29-2003, 09:35 AM:

I found an old Drive-In heater at an antique store the other day and I was wondering the history behind this.

How were they powered? ( 220v ) How were they distributed?

I have noticed more Drive-Ins staying open during the first part of winter and some open all year. Are there any new in car heaters being marketed.

Posted by Ken Layton (Member # 133) on 09-29-2003, 01:46 PM:

They are usually 220 volt. Some were permanently attached to the speaker post and some were handed out at the boxoffice or the snack bar & the patron plugged them into a weatherproof quick-connect on the speaker post. EPRAD and SPECO (formerly known as Drive-in Theater Mfg) both made in car heaters. SPECO still has repair parts for both brands. I don't know if they still make new heaters, but I think they might.

Posted by Jack Ondracek (Member # 1466) on 09-29-2003, 02:24 PM:

Expanding on Ken's post:
There were a few drive-ins in Washington that provided heaters. Most of them were located in the eastern half of the state. There is one left on our side that has the wiring to show they once provided them, but I don't think they still do. Liability, maintenance and power costs have killed the idea. Like window speakers and "Raingards", car heaters have become more valued as souvenirs than for their intended purpose.

Posted by Ken Layton (Member # 133) on 09-29-2003, 04:34 PM:

The manuals for the heaters are here on film-tech.

Posted by Adam Martin (Member # 641) on 09-29-2003, 05:06 PM:

Here are some photos of the heater setup at the Y&W Drive-In in Merrillville, Indiana. There is a "heater room" attached to the snack bar, so I assume that the heaters were distributed from either there or the snack bar to customers who wanted them. Each speaker pole had a plug dangling from it to plug the heater into. You can see from the heater plug that it is 220v. There is an on/off switch on the back of the heater, but no identification of the theater it belongs to or manufacturer.

Posted by Steve Anderson (Member # 364) on 09-29-2003, 06:06 PM:

Cool pictures Adam!
I was really young but I can remember my Dad getting the heater when you arrived at the ticket booth but I think when you exit the lot you went by the other side of the booth and returned the heater. I can't remember because I was asleep at the time....

Posted by Jon Bartow (Member # 241) on 09-29-2003, 08:17 PM:

A drive-in I serviced up until this summer still had the 220v lines in the field (the plugs were long gone from the poles though) and the breakers in the booth were just "locked" off. Up until about 10 years ago this drivein stayed open year-round (and in Central Michigan!) They also are still using the speakers-on-poles for both fields (1200 speakers in total [not a typo - 1200!]) in addition to FM sound that was installed this year to replace the ailing AM system.

Posted by Scott Norwood (Member # 30) on 09-29-2003, 09:21 PM:

Is anyone else bothered by the idea of having 220-volt lines hanging off of the speaker poles, just waiting for some child to zap himself?

Posted by Ken Layton (Member # 133) on 09-30-2003, 12:11 AM:

The heater that was pictured is an Eprad "Hot Shot".

Posted by Robert Golding (Member # 746) on 09-30-2003, 02:49 AM:

We had a Drive In, in Yuba City, Cal that had kerosene portable heaters until 1973. They outlawed them that yr. Believe it or not, never had a fire caused by one. I still have one in my display case.

Posted by Erick Akers (Member # 875) on 09-30-2003, 05:29 AM:

Another interesting fact is that junction boxes on the speaker poles with red difuser lights indicated what poles had a heater plug.

Posted by John Hawkinson (Member # 1135) on 09-30-2003, 12:48 PM:

Scott, 220V isn't substantially worse the 120V. It's the current that gets you, and its less at 220V anyhow.

--jhawk

Posted by John Pytlak (Member # 331) on 10-01-2003, 04:48 PM:

quote:
Scott, 220V isn't substantially worse the 120V. It's the current that gets you, and its less at 220V anyhow.

Yes, it's the current that kills, but a higher voltage is more dangerous because it can overcome the skin's natural resistance more easily. And in the case of 220 volt service, both leads are "hot" relative to ground.

Posted by Tim Reed (Member # 137) on 10-10-2003, 01:42 PM:

Bzzapt!

Posted by Steve Kraus (Member # 476) on 10-11-2003, 01:58 AM:

220V will push double the current through a given resistance. But if as John suggests they are using two hot legs as in the typical 110/220 (120/240) Volt setup then the most likely shock scenario (contact with a single conductor) they would be getting only a 110-120 V shock. Someone might bridge both prongs of a partially inserted plug but the higher voltage shock would only be across the finger unless someone was handling the plug with both hands.

Obviously if someone was putting this in nowadays they would simply use 120V and ground fault interruptors. Or maybe an isolation transformer whose secondary side has no grounded leg.

And then there is the matter of the air conditioned drive in!

Posted by Erick Akers (Member # 875) on 10-11-2003, 02:26 AM:

Drive In A/C...
Frostie Man Frostie!!!!

Posted by Phil Hill (Member # 371) on 10-11-2003, 02:44 AM:

I seriously doubt that anyone would be stupid enough to run those high-wattage devices on 120 volts in these times.

I’m sure a modern-day “real” engineer would use 240 volts with a local ground-fault interrupter and fuse/breaker protection...as well as a local disconnect required by some codes.

Also, NEC and all local codes that I’m aware of would not allow a “floating” isolation transformer secondary...it is unsafe. One leg MUST be grounded for a reference. Besides, that method would be ridiculous cuz of the cost involved.

>>> Phil

Posted by Steve Kraus (Member # 476) on 10-11-2003, 10:52 AM:

Phil, if you're worried about the current requirements of 120V operation bear in mind that it would be wired as 120/240 3 wire (2 hots and a neutral) with half the posts on one side and half on the other. The maximum current draw will be the same as an all-240 V setup and the neutral will only be carrying the unbalanced current when there happen to be more heaters running on one leg than the other. To the degree there are similar draws on both legs it's as though they're in series across the 240.

Thus there is no technical advantage to your wanting to use the higher voltage unless you want to do a 240/480 setup but that would really put you into dangerous territory.

As for the isolation transformer idea you're right that with these loads it would be too expensive. I'm not sure why it would be more dangerous. If you're talking about a step-down from a HV primary then yes, if HV somehow found its way onto the secondary then grounding one leg limits the voltage above ground to no more than the secondary value. But if we are going from 240 (ulimately coming from some other transformer) to 240-isolated then a failure in the iso transformer could put no more than 240 above ground on an output line because that is what the input is limited to by virtue of the original step down transformer having one leg of the secondary grounded.

I do note there is some limited use (in recording studios etc.) of 120 V transformer which are center-tap grounded meaning that the maximum shock is 60 Vrms but this is for noise isolation as the GFCI's are the best way to manage shock risk.

Posted by Phil Hill (Member # 371) on 10-11-2003, 07:40 PM:

Steve, I was actually more concerned about hardware and the installation costs. [Big Grin]

Both a 120-volt or a 240 volt system would be inherently safe if installed correctly. But, since there is no way to be certain that the same number of heaters would be on at the same time on both sides of the line in the 120-volt configuration, the big technical advantage of course is the automatic balancing of the load distribution in the 240-volt configuration. This is very important not only from a technical standpoint, but from a power cost consideration. Most power-bill rates for “industrial” installations are based “leg demand” and balance. Power companies don’t want someone to make their life difficult by presenting highly unbalanced loads on their systems.

By way of an example, let me put this down so I can understand what I want to say... [sleep]

Assumptions:
1) 120/240 volt single phase "split" system.
2) There are 200 heaters in this Drive-In.
3) Each heater takes 600 watts. 5A@120V. 2.5A@240V.
4) We want the heaters in only 5 rows. Each row has 2 sections that feed from the center at the projection booth. Each section has 10 heaters. 20 "sections" total. The last heater in each section is 100 ft from the booth and the branch-circuit breakers.

Total Power for the heater system would be 200htrs x 600watts = 120kW. 1000 amps @ 120V…500 amps @ 240V. While the main panel and feeders would be sized the same there would be one less conductor and bus bars and connections on the 240V system since a neutral is not required. Each hot leg, and neutral, would still have to sized for the 500 amp rating…700CM copper?

Each row "section" would have a heater load of 10htrs x 600watts = 6kW. 50A@120V. 25A@240V. (20 sections = 120kW). Again, each branch circuit would still have to have the same size wire for the hot legs but no neutral. Assume no more than a 2% voltage drop at the last heater, the wire size would have to be min #8, #6 AWG copper. Also, since the last heater/post must still be able to trip the branch breaker (40Amp?) in case of a fault, that size wire would have to be carried all the way thru all the branch circuits.

That "extra" neutral conductor alone results in a 33% increase in hard costs. Not even taking in consideration of conduit loading/sizing, extra labor costs to install, etc. (Note: there still would have to be a ground conductor in both cases…3 vs. 4 conductors.

I like the idea of a 480-volt system, but I think that would be "pushing the envelope" …beside the codes get really weird once you get past to 300 volt mark. Although 480/277 3-phase might be an option. [evil]

About the grounding of the isolation/distribution transformers. If there is no reference to ground on the secondary, there exists a potential shock/electrocution hazard by way of 2 or more equipment faults such as a conductor "touching" a heater case and other one touching the pole. Some poor patron could be fried if they were to get across that. By grounding a leg, the system has a "reference" with which to draw enough current thru to trip the safety devices including the GFIs. Also it is wise for lightning protection or for insulation leakage currents and pri-sec xmfr failure.

The studio example you site is very common for avoiding hum and noise. But note, the center-tap is the ground reference.

Now that I have totally confused myself, I hope you can make out the jest of what I'm trying to say! [Big Grin]

>>> Phil

[ 10-12-2003, 08:43 AM: Message edited by: Phil Hill ]