The Stovebolt Site Forums The Shop Area The Electrical Bay Fire Engine Wiring - longish, but kinda fun

Working my way toward rewiring the auxillary electrical stuff on my '44-ish Chevy. Working on a wiring diagram, wire sizes, etc. I'm ordering a new harness for the stock wiring, but the extra lights, sirens, etc. I'm doing myself, as a "secondary" harness.

A few caveats:
1- my standard is "as absolutely original as possible". Don't bother suggesting I put in an alternator, or switch to 12-volt. Ain't gonna happen.
2- don't really know how it was originally wired. Been thru several owners, lots of hack repair jobs.

So, QUESTION #1:

Where do you recommend I get power for the (not joking) 4 turn signals/flashers, two hose-bed lights, two rear waring lights, spot-light, front bumper warning light, siren, and possible beacon?!!

They were originally wired here and there . . . some to the regulator, some to the light switch, some not hooked up, etc.

I would be FINE wiring from a fuze block straight from the battery, but don't quite understand if the ammeter would register the total current pull then?! I obviously want to know when I'm pulling down the battery, just not sure if the ammeter shows the total pull if EVERYTHING isn't wired thru it? Anyway, not sure the ammeter would HANDLE everything wired thru it? I'm kinda hoping that since the electrons are flowing thru everything, and the ammeter is in touch with the battery, that when I'm pulling hard from the battery, the ammeter will still reflect appropriate charge and discharge. Not clear on this though.

QUESTION #2:

What happens when I run all this stuff that the 35-amp generator is CLEARLY not capable of powering? I assume I just start pulling off the battery, which is fine until it dies. I'm also assuming that, as long as I don't run the battery down too far, and turn enough stuff off soon enough that the generator can start powering the battery back up (ie: use LESS than 35 amps). OR, do I burn the generator up if I ask too much from it? I'm thinking/hoping that it will spin away at full capacity and not burn up as long as the current it's generating is being used up, yes?

I've tested each item (except beacon) with an amp meter. Total pull, if I put EVERYTHING ON, not including the 15 amps of the headlights, Ign., dash, & taillight, and assuming sufficient wire size to keep resistance down, is . . .

are you ready?!!! . . .

67 AMPS!!!

Of course, the biggest draw is the siren, at 20 amps, and it's an on-a-bit-off-a-bit type thing, so you get the up and down wail. And, many of the warning lights are on flashers, which, I'm assuming, use a little less than full amperage (over time, I mean).

As long as I KNOW when I'm using more juice than I can afford, I think I can be alright. Just don't know how to wire the stuff so I KNOW that?

Any thoughts? Thanks in advance, by-the-way.

-Michael

Michael,

I think a generator can output itself to death. The voltage regulator has a current relay that is set to a max, but a generator that runs at max for awhile can burn to the ground.

I would research getting a higher output generator and regulator.

Tagging all the lights and sirens off a battery connection that goes to a fuse block by way of a thermal overlaod or link sounds like the way to go.

The ammeter will read a discharge when it see's a load on the - side of the meter. Hooking all your auxillary stuff on the battery, which is on the + side would cause the meter to show a high charge as power is taken from the battery, but replaced by the generator through the ammeter. This is the same as a discharge, but in reverse...you still know what's going on.

My concern would be the size of the stock wires, the capacity of the ammeter and the generator.

Everything could work, it's just that everything is too small for the maximum intended load. I think you will find fire engines have almost a sencond circuit just for emergency stuff, and this probably includes some type of second ammeter.

I remember some previous posts about electrical systems on old fire trucks. They had huge strange generators and meters that had a higher capacity.

At some parade, you will invaribably want to run all the lights, flashers and siren at the same time. You don't want your fire engine catching fire when that happens.

Stuart

I don't know . . . I think a fire truck on fire at a parade has a certain poetry to it, yes?

What I keep thinking is, the company that converted this to a fire truck, made a lot of 'em, and all on commercial chassis. They didn't have the alternator option, were stuck with 6-volt, and, as far as I know, didn't consider anything but the stock generator. Yet, they piled all this stuff on. So they must have had a thought about how it would all work.

With the help of the "Automotive Electrical Handbook", (HP Books), I used Ohm's Law and equations to work out the proper wire sizes, then went at least one size larger, to be conservative. Mostly 10 & 12 gage, since it's a long way to the back of the truck. So I'm not worried about wires burning up.

For arguments' sake, what's the highest output 6-volt generator anyone's seen on a stovebolt?

-Michael

Just an idea here but why not put a second 6V battery in parallel with the first battery and run all your aux loads off of it through a seperate ammeter like atomarc suggested? That won't keep your generator from working just as hard but would keep everything lit and blarin' away a lot longer and double your cranking amps at the same time. I dunno, whadya think?

Yeah, a second battery would be a good idea. Just not sure where to put it. Still have the bat. in the original spot beneath the cab - maybe room for two down there?

Not to sound stupid, but should a 100-amp hour battery give 100 amps for an hour? I know realistically not to expect that, just not sure how the name equates, other than "more is better".

-Michael

Mike - a 100 AH battery will supply 100 amps total over some specified time [usually 20 hours, so 5 amps per hour] - NOT a continuous 100 amps, but a total, and by that time the battery will be "deep cycled" and never charge to full capacity again if it's not a deep cycle batt .... the reserve capacity will tell you how many amps it will deliver continuously over what length of time before the same deep discharge

what's more important for a normal automotive [starting] batt is the CCA rating: the maximum amperes that can be continuously removed from a battery for 30 seconds at 0°F ... for your application you might consider finding a heavier duty generator with higher utput - or get a local shop to build you one

Bill

on my engine "ASHTON" first off, it came with a bosch 55 amp generator and is six volt. all the wiring is still original and power comes from the amp meter terminal to its specified appliance switch to the appliance. its all routed nice and neat under the dash. the siren is energized by a solenoid with a heavy wire(looks like a twelve volt battery cable or the next smaller size wire) from the hot terminal off the starter directly to the siren. dont use anything small or you will smoke test the wire when you hit the siren! i burned up some wiring testing another siren with small wires. they draw a lot of current getting wound up.

when everything is energized including the siren it pulls a steady 25+ amps. thats how i exercise the voltage regulator.

if your concerned about pulling too much current then eliminate what you dont deem critical for the effect your looking for.

for warning lights i have a beacon on the top of the roof, two 5" spots with red lenses on the cab above the doors and two flashing beaons on the rear grab rail and no light on the siren.

during a parade i have either my running lights or headlights, four ways on along with all the emergencey lights on which is then pulling between 10-15 amps. wind up the federal and then it hits max draw.

Given your goal of staying as original as possible, I would take the generator you have to a shop that rebuilds them (and knows what they are doing), and ask them to build a 60 amp (or 75 amp for spare capacity) 6 volt generator. Then get the best and most powerful battery you can buy (power-wise) that fits in the original case.

If you know someone who knows automotive electrical systems, consult them on the whole project so that you get your wire gauges right and have the proper grounding so the system works.

Here's one place that might be able to do the job - http://www.auctioniowa.com/autoiowa.html (I'm sure there are others.)

I am restoring a 1946 Chev. fire pumper. The truck wiring is still stock with a top light & siren. A small flasher light on the back rail and thats about it. The rest of the lights, head lights and other is standard much like a regular truck. I to date have not given much though about the over load if any. The only concern would be parade use and running the siren without stopping. ( remember the siren may not be designed for such use either ) I may put an additional six volt battery in as a back up. The amount of overworking the generator would be at a minumn. They used these fire trucks for years without any trouble so ....... a parade or two should not be a problem.

When I had my Fire Truck I wired a second battery in parallel for extra amps. I had room behind the seat and ran cables to the battery under the floor.
Cleon

Second Battery is good idea, again, if I can figure out somewhere reasonable to put it. Beefier Generator would help, too.

Thing that gets me is, what did they do originally? Kills me not to know. Maybe they mounted a second generator! OR, just went through a lot of batteries!!!

Does everyone agree with Stuart that the generator would fry after a while at full capacity? If I knew for sure that the existing generator would operate at capacity without spontaneously combusting, I'd be ok with stock - I can regulate as needed not to overburden the bat. for too long.

Thanks everyone!

-Michael

if they or nobody else did nothing to the generator then it should be ok. i seriously doubt they had a second gen or an additional battery.

id bet if they did anything throught out its life it would be to add more lighting than what the electrical system was designed to handle.

Michael,

Have you found the Delco number on your generator. I have a list of numbers with corresponding outputs. The largest I have found is a 6 volt unit with a max output of 50 amps. These are listed quite often and that is a respectable amount of power.

If the generator came with the truck maybe it's a big mother!

Stuart

Stuart,

Brilliant, as always. I think a higher output generator would be a good compromise between out-and-out originality, and the practical improvement to (almost) meet the demand.

I'll start looking for the 50-amp 6-volt gen. How certain are you it will bolt up to the 216?

Thanks as always. I'll submit some pix as I progress down this path.

-Michael