Thread: Telma Retarder

  1. #1
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    Default Telma Retarder

    Looking for some better insight about how exactly a Telma Driveline retarder works. We have them on a few of our rigs and I understand that it causes a magnetic field to help slow the driveline..is this true? Can anyone shed some better mechanical light on the subject.

    Also, wonderin if anyone has a driveline retarder and jacobs brake on the same rig. If so, how is the stopping performance?

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    Talking telma

    The Telma retarder utilizes electrical current to produce a magnetic feild that slows the rotation speed of the driveline. The current is staged , usually four stages, to increase the current to the magnetic field. They also have what is called a focal mount unit that bolts directly to the rear differential to do the same thing. The system usually cuts off at speeds below 5 mph. If the amperage output of the alternator is sufficient and the batteries are of a good quality then the system does not usually suffer any adverse effects. I was told by our local Detroit dealer that they preferred not having a combination of the Telma and the Jake brake combined. We have run Telma for years with great success but don' t comingal systems.

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    Default

    More specifically, a Telma has four simple, stationary electromagnets in close proximity to a spinning cast iron disc that is in the drive shaft and is very similar to a large disc brake rotor. When you want to slow down you energize these electromagnets which cause a magnetic field to "cut through" the iron. When a magnetic field cuts through a moving metal object, it sets up a current in that object, and since the rotor is one big hunk of cast iron, that current is immediately shorted out by itself. This shorted current serves to heat the iron and the energy for that heating is coming from the forward motion of the vehicle which slows it down without any mechanical contact between parts.

    I do not have a Jake and Telma on the same vehicle, but I do have an Allison retarder on one with a Jake. (The Jake was added later because the Allison retarder kept puking its guts, expensively, so I instructed the drivers not to use it any more except for emergencies, and if it dies again I will remove it then.) Anyway if you use both of them at the same time, in the words of the Detroit shop, it will "stand it on its nose". With attentive driving, it is not necessary to use the retarder. However it would be neat to have a Telma and Jake on the same vehicle. There might be issues with drive shaft torque though. Modern Jakes are so powerful, it would hardly be necessary.

    Birken

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    Default Telmas

    we are currently building a new tanker (water tender for you ppl out west) and we have done exactly that. We have installed a jake and a telma to work in conjunction with each other. We will let you know if it works. The idea came from our 03 pierce 105' ladder, she is equipped with a retarder and jake and the combination works just beautifuly.

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    Default Telma Retarder

    For the best explanation of how a Telma works, go to www.telmausa.com.
    We have 3 Telmas and love them.

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