The Series Parallel Switch.

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kw573
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The Series Parallel Switch.

Post by kw573 » Sun Nov 13, 2016 3:39 pm

Hi all,

A little while ago, I gave a short presentation to my local MJCQInc. club 'Tech Night' at the annual Swap Meet and Field days. Instead of just throwing out the stuff I made for it, I thought there may be some interest in it, both now and in the future, for a wider audience.

As part of the rebuild of my 969 wrecker, I repaired the water/rust damaged series-parallel switch (sps) and got it working again. In the process, I learned how it works and what it does. Its' a complicated big beast that wears several 'hats'.

Let me say straight up that I am not an auto-electrician, but not clue-less either. What is presented here is what I have learned over time.

Firstly, some electrical theory.

Automotively, electricity is measured in –
volts (V) which could be described as electrical pressure
amps (A) which could be described as electrical volume
watts (w) which is the measure of electrical power.

Going back, briefly, to your school science, these relate to each other in the formula V x A = w
Hang on, stay with me for a bit. . . .

What this means is that to get a certain amount of power (w) to, say, start a Jeep, we need the right combination of volts and amps to give the needed watts (power).
If we have lower volts, as in the 6volt Jeep, then we need more amps to get the needed watts (power). To get the bigger amperage (electrical volume), we need bigger cables. That is why 6v Jeeps have such large starter cables, and why some jeeps have trouble starting with smaller cables fitted, and are so susceptible to poor connections.
However, if we increase the volts (electrical pressure) instead, it is easier to get the needed power to the starter, higher voltage doesn’t need the bigger cables. Sorta like getting more water out of the same size hose by increasing the water pressure.
This difficulty in getting sufficient power to the starter of the 969 at 6v is why, I guess, they went to a sps.

One more bit of theory.
If two batteries are connected in parallel (side-by-side), then the voltage stays the same, 6v and 6v = 6v. But the amperage is the total of both batteries, heaps. This needs big cables and switches to make it work properly.
If two batteries are connected in series (end-to-end), then the voltage is the total of both batteries, 6v + 6v = 12v. But the amperage is the same as only one battery. The 12v system will deliver the power to the starter much more efficiently than the 6v system. This is also why many modern trucks are 24v, viz.12v + 12v.

And this is why the larger trucks with 6v systems used a sps to get 12v for proper starting.
Why they didn’t go to a simple 12v system like radio cars, the GPA and others, I don’t know.

End of theory.


WHAT IT DOES.

The sps is floor mounted and does several things when depressed.
In order, it . . . .
1) . . disconnects the Batt B charging system on both sides (power and earth) of the B battery. (The blue circuit)
2) . . connects the two batteries together by closing the series circuit (The red circuit). The two batteries are NOT connected in parallel by the starter cables at any time.
3) . . then connects power to the solenoid at the starter, engaging the starter. (the yellow circuit)
4) . . locks the plunger in the ‘depressed’ position.

Further, the B(-) terminal, which is now 12v, is fed from the starter solenoid battery lead and provides the power to the (sw.) terminal (yellow) which engages the solenoid! This same B- wire has a different job when the sps is released.

Image




When released, it . . .
1) . . unlocks the plunger.
2) . . disconnects power to the solenoid. (Yellow)
3) . . opens the series connection to the two batteries. (red)
4) . . reconnects the charging system to the B Battery in two places. (blue)

For step 4) above: How? The B(-) terminal is now connected to the A(-) terminal, allowing the two batteries to be charged in parallel. This is the second use of the B- wire that goes from the solenoid to the B- terminal on the sps.
Also, the B(+) terminal, which is earth side of the battery, is now connected to the Amp. terminal which goes to the Batt B amp gauge and then to earth, so completing the charge circuit for Batt. B.

Image



Complicated beast, it is.


How the starter cables are connected.
The truck has a main battery, used in the usual operation of the vehicle, and a ‘Battery B’ which is used only for starting. To confuse things more is that it is a positive (+) earth system. Grrrr.

Starting with the main battery (A), its’ +ve is earthed and (–) goes to the A(-) terminal on the sps. That’s it for that main battery.!!
For the B battery, the (+) goes to the sps Batt (+) terminal and the (-) goes to the input terminal on the starter solenoid.
You can see this on the wiring diagram below taken from the parts manual.

Image


The next post sets out to the plunger lock mechanism.
Time to give our heads a rest.
Sam.
1942 Script GPW (Daily driver).
MB-T trailer.
Diamond T 969. ('The Glorifier')
Diamond T 969, rusty, complete, for sale.
Kenworth M1A1 Heavy Wrecker x 2.
M2A1 white HT. ('Clarrie')
Light Recovery Trailer (Ford?).
3ton GS (Blitz) Trailer.
150gal water tanker trailer.
Air compressor trailer, 100c.f.m.


rjbeamer
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Re: The Series Parallel Switch.

Post by rjbeamer » Mon Nov 14, 2016 9:57 am

Good day Sam. Addressing your theory question on why they just didn't go with a total 12 volt system. Might have to do with on large trucks they used and or towed trailers that were also used with trucks that had the standard 6 volt system. 6 volt systems were the norm and a truck with a 12 volt system would have been the odd ball. Just my thoughts.

Roger

kw573
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Re: The Series Parallel Switch.

Post by kw573 » Mon Nov 14, 2016 4:58 pm

Hmmm, interesting Roger. Thanks.
Raises the question of towing a jeep trailer (6v) with a GPA (12v).

Anyway, I got pictures of the switch. First from the top showing the plunger that is stood on to operate it, and the mounting bolt holes. It mounts on a bracket off the gearbox top.

Image


And the terminals underneath. The terminal on the side is, IIRC, the Batt. B earth that goes to the Batt. B amp gauge. This terminal, and the B- terminal are a strange spring-loaded retractable pin arrangement, which I am clueless as to why they used it.

Image


Questions/comments welcome.

Sam.
1942 Script GPW (Daily driver).
MB-T trailer.
Diamond T 969. ('The Glorifier')
Diamond T 969, rusty, complete, for sale.
Kenworth M1A1 Heavy Wrecker x 2.
M2A1 white HT. ('Clarrie')
Light Recovery Trailer (Ford?).
3ton GS (Blitz) Trailer.
150gal water tanker trailer.
Air compressor trailer, 100c.f.m.

wreckerman
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Re: The Series Parallel Switch.

Post by wreckerman » Tue Nov 15, 2016 1:22 pm

Lots of good information.

I rebuilt my switch many years ago but I was also lucky at the time to find a couple of NOS switches. A few years ago I ran into an electric solenoid operated dual voltage switch at a garage sale. Wish now I had bought it.

Dan

kw573
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Re: The Series Parallel Switch.

Post by kw573 » Wed Nov 16, 2016 10:54 am

Hi Dan,
I've been told of switches like that used in tractors and Mercedes Benz trucks in the 1950s and 1960s.
No doubt there are many more.
You blokes in USA and Europe are so spoiled for NOS stuff! :?

Sam.
1942 Script GPW (Daily driver).
MB-T trailer.
Diamond T 969. ('The Glorifier')
Diamond T 969, rusty, complete, for sale.
Kenworth M1A1 Heavy Wrecker x 2.
M2A1 white HT. ('Clarrie')
Light Recovery Trailer (Ford?).
3ton GS (Blitz) Trailer.
150gal water tanker trailer.
Air compressor trailer, 100c.f.m.

BCA
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Re: The Series Parallel Switch.

Post by BCA » Wed Nov 16, 2016 3:07 pm

I have several perfect condition NOS series parallel switches available. Send me a PM if interested. They fit many large Ww2 trucks including the Diamond T. ... Brian

wreckerman
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Re: The Series Parallel Switch.

Post by wreckerman » Wed Nov 16, 2016 3:41 pm

Hi Brian.

curious minds would like to know what other vehicles used them.

Thank you

Dan

kw573
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Re: The Series Parallel Switch.

Post by kw573 » Wed Nov 16, 2016 5:32 pm

Thanks for the offer Brian.
You wouldn't happen to have a 969 Transfer case PTO control cable spare?
Sam.
1942 Script GPW (Daily driver).
MB-T trailer.
Diamond T 969. ('The Glorifier')
Diamond T 969, rusty, complete, for sale.
Kenworth M1A1 Heavy Wrecker x 2.
M2A1 white HT. ('Clarrie')
Light Recovery Trailer (Ford?).
3ton GS (Blitz) Trailer.
150gal water tanker trailer.
Air compressor trailer, 100c.f.m.

BCA
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Posts: 170
Joined: Sun Apr 24, 2011 3:45 pm
Location: Milton, Ontario, Canada

Re: The Series Parallel Switch.

Post by BCA » Thu Nov 17, 2016 10:25 am

Dan: the switch fit G159 and G509 Diamond T's as well as a variety of Autocar,. Corbitt, and Mack trucks (G512, G514, G690). It is such a specialized switch that I suspect it was common on a variety of civilian trucks also.
Sam: Sorry no PTO cables.

rjbeamer
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Re: The Series Parallel Switch.

Post by rjbeamer » Fri Nov 18, 2016 6:09 pm

Good day Sam. As to the theory on 12 volt systems and using with the standard 6 volt trailers. Good point on GPA"s. I posed the question on the GPA board as to how they addressed towing 6 volt trailers with GPA's. I only had 1 response and he said that GPA's did not have trailer wiring provisions. However they do have a pintle hitch. Just an FYI.

Roger

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Re: The Series Parallel Switch.

Post by CplDixon » Tue Jul 18, 2017 4:35 am

rjbeamer wrote:
Fri Nov 18, 2016 6:09 pm
Good day Sam. As to the theory on 12 volt systems and using with the standard 6 volt trailers. Good point on GPA"s. I posed the question on the GPA board as to how they addressed towing 6 volt trailers with GPA's. I only had 1 response and he said that GPA's did not have trailer wiring provisions. However they do have a pintle hitch. Just an FYI.

Roger
Same for WLF M1A1

Single 12V system,pintle hitch but no trailer connection...

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Re: The Series Parallel Switch.

Post by danielmartin322 » Sat Sep 02, 2017 5:52 pm

Sam, As I attempt to get my White 444T (Autocar U7144T) to running condition, this write-up has saved me a lot of time. Many thanks!
As for the 6 volt battery / 12 volt battery question: I would pose that it is simple logistics. The contract between the manufacturers and the government had specifications in the statement of work. Most likely the requirement for the 6 volt batteries was to reduce an additional support item requiring manufacture and shipment to the combat zone. If you only have to ship 6 volt batteries...makes it easier and cheaper.
And you can always salvage the battery from a wreaked vehicle to get another serviceable.
Thanks again for the article. Is a bid help.
Dan

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Re: The Series Parallel Switch.

Post by radarsgunner1 » Sun Sep 03, 2017 10:20 am

There were resister boxs to step down the voltage for 12v vehicles to tow 6v trailers
Paul Rea
MVPA #31101
1941 CCKW 352
1942 CCKW 353
1944 Ward Lafrance M1A1
1944 Brockway C666
1944 Ben Hur
1944 Willys MB
1945 CCKW Tipper


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