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dyno question

General engine tech -- Drag Racing to Circle Track

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Belgian1979
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dyno question

Post by Belgian1979 » Thu Dec 05, 2019 3:11 am

Anyone ever rebuilt a telma retarder to be used for a rolling road dyno. A while back I acquired a cc300 old truck telma that I'm going to use for this purpose (3000 NM). However, I need to take off the coils and do some repairs which involved refitting them. Was looking for tips on the correct pieces and how to do it.

Thanks.

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Re: dyno question

Post by SchmidtMotorWorks » Fri Dec 06, 2019 9:05 am

I have also looked into this.
From the little bits of information I have found there is a significant bit of electronics required.

The 24 volt truck control is not what people seem to use.
Instead they rewire the coils in series? And then use a power supply of 192 volts.
I don't know if the voltage is variable or if the current is pulsed.

I have water brake dyno that I would like to convert.
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Re: dyno question

Post by Belgian1979 » Fri Dec 06, 2019 4:19 pm

Hi,

Yes, it's preferred to put it into series, but the main reason is that you need to be able to keep the amps down when using it at full power. The amount of amps run through it determines how much braking it does. So you could do this with a 2 resistors in parallel where one is adjustable.
However there's more to it, I need to use a transformer to get the correct voltage and then a rectifier to go from AC to DC.

I have to take the coils of since the anchor has cracks in it that need repairing. When taking off the coils, the paper that insulates it from the steel core gets damaged. It seems to need to sit quite tight onto those steel cores so it doesn't move around when energized.

The advantage of these is that they don't require water to cool them. The pull their own air through the rotors. I've gotten myself an old brake bench that I intend to use as a basis for the rolling road. The rollers will be connected to the brake.

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Re: dyno question

Post by SchmidtMotorWorks » Sat Dec 07, 2019 2:09 am

What do you have for a variable resistor?

I wonder if a VFD, Variac or other variable device could supply the power.
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Re: dyno question

Post by Belgian1979 » Sat Dec 07, 2019 11:57 am

I still have to research those parts. For now I'm concentrating on rebuilding the brake and mounting it on the roller bench. From that point onwards I will be looking into the power supply and regulation of the brake. This last one will have to be something that can be done through a laptop as I want to be able to control the brake and at the same time do the ECU tuning.

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Re: dyno question

Post by SchmidtMotorWorks » Sat Feb 15, 2020 2:07 pm

http://www.schmidtmotorworks.com Prototypes, Tooling, Molds.

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Re: dyno question

Post by Belgian1979 » Mon Mar 02, 2020 1:53 pm

I'm in the process of restoring it. The problem with this particular retarder is that one side where it normally attaches broke free. So I need to weld it back together in that location. Unfortunately this also damaged some of the coils. I have an outstanding order for some of the parts. Hopefully I can do some more work on it in the next months.

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Re: dyno question

Post by Belgian1979 » Sat Apr 18, 2020 3:01 pm

A short update to this: I have take it mostly appart. Needs work on the bearings etc. The parts are not in probably due to the corona crisis.

Meanwhile I've located a second Telma unit that looks similar to mine for dirt cheap. I'm going to have a look at it in a week or so. This might be a good thing as I could employ 2 identical brakes to load each rear wheel and do away with the rollers.

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Re: dyno question

Post by Protech Racing » Sat Apr 18, 2020 3:25 pm

To do that will require two data collection systems and double the data variances along with the hardware .
Much better IMHO, to Hook the rollers , wire up the telma , add the inertia values, etc.

https://yourdyno.com/

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Re: dyno question

Post by BCjohnny » Sat Apr 18, 2020 4:35 pm

The official ‘Telma’ factory manual coil removal procedure is to put a cold chisel through the coil, and unwrap …… obviously the coil cannot be refitted, but the manual doesn't anticipate that

The simplest way to regulate the braking force is to use an AC variac, and then put it through a full wave bridge …... yes coils wired in series to keep the amps sensible

The series voltage of 192v I'm guessing can be 'overdriven' for short periods, if needed

This is how I’m initially proceeding, and then have a word with someone who actually knows what they’re on about and hopefully come up with some kind of adjustable ‘decaying voltage’ feed

This, with the inertial mass of the four 'Telma' rotors (not inconsiderable) should be tunable to give a rate of acceleration hopefully similar to what you might see on a dyno (300 ~ 600)

I'll obviously retain some kind of 'steady state' capability

I’m not too bothered about calibrating it, to begin with, aside from ‘ballpark’ figures, it’ll be a ‘comparator’ not a scientific instrument ……..

Being air cooled is good and bad

[Edit : sp]
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Re: dyno question

Post by Belgian1979 » Sat Apr 18, 2020 5:32 pm

Hi,

Very usefull info.
Do you have the factory manual? Mine are CC300's.

As for the coils, these can be easily taken off in one piece. They basically slide off with a slight amount of force. The hardest part is the paper isolation between the coil and metal core. I'm going to use big diameter heat shrink tubing for that.

The advantage with 2 of these is that there is no slip and no risk of tire explosion to contend with and yes it'll require 2 data acquisition systems to use both of them.

As for power supply I was thinking about a transformer to go from 400 VAC to 192 VAC and then a rectifier to get 192 VDC. In principle the amount of magnetic force is equivalent to the amps. So a variable resistor parallel to the brake should allow you to set the force quite accurately.

Not sure about the data acquisition system yet. I'm quite good at PLC programming which would allow me to regulate the brake and even readout the loadcell. I think I could even send out a 0-5V signal that would be proportional to the amount of power that I would be able to read in as a digital signal via an A/D converter. But that is still pretty far away.

The retarders are a fairly simple solution. A water brake (of which I have a 400 hp heenan froude here as well) is a lot more elaborate to use especially with a rolling road type of dyno.

Attached a youtube move about a couple of guys that did it.
The units these guys use are the same as mine (maybe smaller but same principle)

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Re: dyno question

Post by Protech Racing » Sat Apr 18, 2020 10:04 pm

"Your dyno" works well.
For basic setup. I have a baseline car. A street car near my target HP of 100-200HP. This one was run on a Known good value Dynojet , and then on mine. Set the corrections and inertia value so the HP reads the same .

"Your dyno" can also measure the coast down values.IE trans/brake/ tire drag.

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Re: dyno question

Post by Belgian1979 » Sun Apr 19, 2020 4:32 am

For my car it's intended to setup my ignition tables/fuel tables, so a lot of steady state tuning.

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Re: dyno question

Post by BCjohnny » Sun Apr 19, 2020 9:28 am

The information I have is mostly on dead trees, and some of the more useful of it has avoided a cursory search …… I’ll look again later

But my understanding is this ……

The CC 300 got re-designated AC 83 – 30

There’s not much specific info on this exact model, but info on the AC 83 –00 & AC 83 – 31 is online, and they look very similar, if not identical

The CC 300 is listed here amongst others

As regards the various, generally well made, online hub dynos my only comment would be I’d never run one without a close fitting scatter shield

I guess it’s more ok to run them unguarded if they’re new, and not oversped, but with the older stuff some of us mess with, maybe not so ……
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Re: dyno question

Post by Belgian1979 » Sun Apr 19, 2020 12:46 pm

That's what I was thinking as well, that a good shield of sorts is needed in case something goes wrong. But similarly with a rolling road this is something you need to do as well.

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