Topic: TNS 291

[David H]

Can someone email a copy to me?    It mentions adding a remote trimmer to the voltage regulator circuit.    It's not in any of the manuals I have.
Thanks
Dave

[Nigel Stevens]

Hi Dave,
I think you may have the reference wrong, as the highest TNS number is 208 issued by dH Support in Jan 2009.
Nigel

[David H]

Thanks Nigel.   It was listed as a MOD 291.  I'm not sure I get the difference between the MOD's and the TNS's.    Anyway, I did order the entire TNS list from DHsupport after my post.  I should have done it sooner.     Is there another publication that contains all of the MOD's or would a more recent repair manual have them?    I have a three different repair manuals and it's not in any of them.

The reason I wanted it was to check the wiring.    The voltage on my system has been too high since I bought it.    The rheostat added by that MOD was already set to the lowest setting so there was nothing left to do but check the carbon pile regulator.    My wiring diagrams don't show the rheostat and I wanted to make sure everything was as it should be. 

I did turn in the adjustable plunger to reduce the voltage in small increments until we got 28.5 volts or so with the rheostat set about halfway between the stops.     It's difficult because to get to the adjustment because you have to crawl up to the firewall.   I first set it where the original paint marks were when I had it out of the plane.   Just setting it there reduced the voltage somewhat.   I guess someone had monkeyed with it at some point. After each engine run and voltage check, I had to get out, remove the pilot's seat pan and crawl up to the voltage regulator and turn it in a bit.    Boy, can I see the advantage of a bench test arrangement now.   It was not a lot of fun crawling up there.    If you ever do this, make sure you give the regulator enough time to warm up.    At first, I wasn't getting any increase in voltage and was worried that I had to flash the generator.   Then I remembered that on some flights it can take several minutes for the generator to start charging.    Warming up the regulator is also mentioned in the instructions on bench checking it.

I don't know how well it will work at higher rpm's.   I only briefly revved the engine up to 2000 RPM with the brakes on and wheels chocked when I was checking the voltage.   We'll see how it goes.     The ceilings were too low to do a test flight today.

I'm planning on ordering a solid state regulator from Zeftonics.   They do make a "b" circuit type generator regulator but apparently it's not a stock item.   I think it's around $300.00.     If I do go with an electronic unit, I'll put in on the firewall - ON THE ENGINE SIDE!!!!!!!

[David H]

PS - I've been searching everywhere for the Lucas regulator mentioned in another thread without any luck.   There are plenty of delco-remy 24VDC generator regulators out there but they're all "a" circuit so they won't work.
Dave

[Nigel Stevens]

Hi Dave,
TNS is short for Technical News Sheet and dH issue them from time to time for specific topics, such as inspections. Sometimes the reccomended fix in the TNS is to apply a MOD. or Modification. On the Chipmunk
all the MODs have numbers begining with H. A full list is provided at the beginning of the TNS binder. In fact it is TNS103.  A MOD is a change from the original specification of the aircraft, so they vary from being paint
scheme changes to changes in material for components or the design of components or the substitution of components.
Some of the TNS are "mandatory" and some are simply recommendations. This refers to mandatory by the CAA in the UK, the status of these can vary by national authority and registration regulations.
For each MOD there is a "Mod. Sheet", which is available from dH Support. These vary from a one page instruction to many pages and associated engineering drawings depending on the MOD complexity.
If you want the MOD sheet form H291 you can get it from dH Support but before you do that the title is "To instroduce a remote trimmer resistance ref No. 5UC/5210 in lieu of 5UC/5780 in the voltage regulator
circuit. Make sure you can get a 5UC/5210 before you start into the MOD.
I also tried to find a Lucas regulator as mentioned elsewhere, but the stock is gone. I think they were fitted to trucks in the 1970's and manufacture was transfered to India and has since stopped. I presume even
trucks use solid state stuff, these days, and have alternators instead of generators.
I'm restoring a Chipmunk and know precisely what you are talking about as far as access to the regulator is concerned. For the moment I have reinstalled the regulator but am concerned that it may not be that
relaible. I was thinking of installing a solid state unit but have not found any information on a suitable item. Can you provide more info on the ZEftonics unit?
Give that I am more mechanical than electrical what is the difference between an "a" and a "b" circuit?
Nigel

[buchan]

Nigel:

If you go to the zeftronics site:

http://www.zeftronics.com/

and open the FAQ's on the left hand side of the page, there is a pretty good, simple explanation of type "A" and type "B" circuit that even us mechanical types can understand.

Don

[David H]

Look at the wiring diagram for the generator and regulator.    Follow the wire from terminal 3 at the regulator, through the suppressor and then to the field terminal on the generator, F1.    Then follow along the field winding to terminal G4, back through the suppressor and then to ground.    The field is grounded on one side.   For our Rotax generators it's bonded to the generator and then to ground.

The zeftronics reference material Don referenced is for an alternator but it's the same for a generator.    As far as I can tell, Ford and Lucas used this arrangement.    I think some old military vehicles did too but I'm not sure.    I've also read where some people rework the generator wiring so it will work with an A circuit but I wouldn't even consider doing that.

Dave

[proplover]

If memory serves me the original adjustment was on the regulator unit itself which was on the cockpit side of the firewall way past the rudder bars - this was eventually deemed a little inaccessable so the regulator unit was changed to a different type and a remote adjuster was positioned behind the front cockpit instrument panel on the left hand side.

[David H]

If memory serves me the original adjustment was on the regulator unit itself which was on the cockpit side of the firewall way past the rudder bars - this was eventually deemed a little inaccessable so the regulator unit was changed to a different type and a remote adjuster was positioned behind the front cockpit instrument panel on the left hand side.

From what I can tell, the original regulator was replaced early on with the F3301.   In 1969 MOD 291 was issued which, I'm guessing since I don't have a copy, added a resistor to the back of the F3301 and the remote rheostat in series with that resistor in near the tach generator.    On the voltage regulator, there are adjustments on the cutout relay, carbon pile and adjustable core.    Only the adjustable core is accessible without removing any covers from the voltage regulator.  I think this is the adjustment you were referring to.   In my case, the rheostat, even at the lowest setting, still allowed the voltage to get too high so I turned in the adjustable core.   I still haven't made a test flight so I'm not sure it's fixed but even on the ground the voltage was much better than it had been.
Dave

[Dick Gower]

Thanks Nigel.   It was listed as a MOD 291.  I'm not sure I get the difference between the MOD's and the TNS's.    Anyway, I did order the entire TNS list from DHsupport after my post.  I should have done it sooner.     Is there another publication that contains all of the MOD's or would a more recent repair manual have them?    I have a three different repair manuals and it's not in any of them.

The reason I wanted it was to check the wiring.    The voltage on my system has been too high since I bought it.    The rheostat added by that MOD was already set to the lowest setting so there was nothing left to do but check the carbon pile regulator.    My wiring diagrams don't show the rheostat and I wanted to make sure everything was as it should be. 

I did turn in the adjustable plunger to reduce the voltage in small increments until we got 28.5 volts or so with the rheostat set about halfway between the stops.     It's difficult because to get to the adjustment because you have to crawl up to the firewall.   I first set it where the original paint marks were when I had it out of the plane.   Just setting it there reduced the voltage somewhat.   I guess someone had monkeyed with it at some point. After each engine run and voltage check, I had to get out, remove the pilot's seat pan and crawl up to the voltage regulator and turn it in a bit.    Boy, can I see the advantage of a bench test arrangement now.   It was not a lot of fun crawling up there.    If you ever do this, make sure you give the regulator enough time to warm up.    At first, I wasn't getting any increase in voltage and was worried that I had to flash the generator.   Then I remembered that on some flights it can take several minutes for the generator to start charging.    Warming up the regulator is also mentioned in the instructions on bench checking it.

I don't know how well it will work at higher rpm's.   I only briefly revved the engine up to 2000 RPM with the brakes on and wheels chocked when I was checking the voltage.   We'll see how it goes.     The ceilings were too low to do a test flight today.

I'm planning on ordering a solid state regulator from Zeftonics.   They do make a "b" circuit type generator regulator but apparently it's not a stock item.   I think it's around $300.00.     If I do go with an electronic unit, I'll put in on the firewall - ON THE ENGINE SIDE!!!!!!!

Just a suggestion before ordering the Zeftronics regulator David: have a look at using an IB308 automotive voltage regulator module and mount this on the existing V-Reg. chassis after removing the carbon pile assembly.  It fits the place quite easily with just an adaptor plate.

The 1B308 is originally a Bosch product but Transpro also make one under the number 1B308-3280-24V.  (not sure whether that is 1B or IB).

This arrangement therefore uses the existing reverse current relay and is a lot simpler. 

I have some reservations about the Zeftronic unit in this application.  There is the additional circuitry that would be redundant and also I suspect that it uses a solid state version of the reverse current relay although all enquiries to Zeftronics went unanswered.

Am about to engineer the 1B308 into my Chippy as above so I will let you know how it goes.

Carbon pile technology is very unreliable because there is an ageing effect and as you have seen, a negative temperature effect.  It is hardly worth the effort to overhaul and test a carbon pile system when there is a  solid state alternative.

Regards,

[proplover]

Hmmmm I don't think the UK CAA wouldnt allow those units to be used over here!! Ohhhhhh the paperwork, the inspections I can see it all now, best to use something thats original, 60years old and been sat in a damp store for all that time. Sorry, feeling moody this morning!!

[Dick Gower]

Yes - the paperwork!  Maybe it is time to go down that same trail with a solid state device that allowed the CAV alternative.

[David H]

Dick,
That's a regulator for an alternator.   Are you sure it will work?     The zeftronics would replace the regulator and reverse current relay.   It's made specifically for generators with a type B circuit. 
Dave

Just a suggestion before ordering the Zeftronics regulator David: have a look at using an IB308 automotive voltage regulator module and mount this on the existing V-Reg. chassis after removing the carbon pile assembly.  It fits the place quite easily with just an adaptor plate.

The 1B308 is originally a Bosch product but Transpro also make one under the number 1B308-3280-24V.  (not sure whether that is 1B or IB).

This arrangement therefore uses the existing reverse current relay and is a lot simpler. 

I have some reservations about the Zeftronic unit in this application.  There is the additional circuitry that would be redundant and also I suspect that it uses a solid state version of the reverse current relay although all enquiries to Zeftronics went unanswered.

Am about to engineer the 1B308 into my Chippy as above so I will let you know how it goes.

Carbon pile technology is very unreliable because there is an ageing effect and as you have seen, a negative temperature effect.  It is hardly worth the effort to overhaul and test a carbon pile system when there is a  solid state alternative.

Regards,

[Dick Gower]

Hi Dave,
".....................   trucks use solid state stuff, these days, and have alternators instead of generators.
I'm restoring a Chipmunk and know precisely what you are talking about as far as access to the regulator is concerned. For the moment I have reinstalled the regulator but am concerned that it may not be that
relaible. I was thinking of installing a solid state unit but have not found any information on a suitable item. Can you provide more info on the ZEftonics unit?

Give that I am more mechanical than electrical what is the difference between an "a" and a "b" circuit?
Nigel

Nigel,

The A and B circuits refer to the two possible ways to design a regulator system. 

In order to keep the generator output voltage between certain narrow limits, the regulator senses the output voltage of the generator and varies the current through the field winding accordingly. 

If the regulator is designed to be wired in the field circuit  between the battery bus and the field winding (like the Chipmunk) it is called a "B circuit".

If it goes between the field winding and ground (like most US aircraft) it is called an "A circuit".

There are advantages and disadvantages for each system.

I have actually changed a Chippy system from B to A (via an EO years ago) in order to use a Delco regulator but with solid state regulators available it would be an easier approach (paperwork I mean) to stay with the B circuit.

I hope that helps.

Regards,

[Bob]

When I had our generator overhauled some years ago the chap that did it said it would be very easy to modify the circuit so a solid state unit could be used.. unfortunately he has suffered a sever stroke since and so cant help. I'm sure if someone came up with a suitable wiring diagram and part numbers a minor mod could be done!! (£86 cheque to the CAA )
I was suprised how helpful they were when I did the Trig transponder mod.