I recently converted my Wren 54II to autostart. When I start the engine the sequence goes as it normally should, but it hangs at 22k rpm or so at about 400C. After moving wires around etc in case of stray voltage, and moving solenoids away from the rpm sensor it didnt fix the problem. I reprogrammed the ecu and checked all parameters and everything is where they should be. Then I noticed in the instructions that Wren states NOT to use a nickel type ecu battery. Well, I used a 7.2volt 6 cell 3300mah nickel battery as thats all I had. Wren states not to use nickel-but doesnt state why.

Im thinking maybe the voltage/current is not sufficient to run the starter or ecu with a nickel battery. I have a friend who uses lipo batteries on his Wren SS with no probs. His lipo battery has diff plugs so we couldnt try it on mine. Im so close to success I can taste it

What is the general concensus?

Thank you,

Kev

Kev:

If you are using a FADEC ECU which is what as far as I know WREN uses, you should be OK with the ni-cad, I really do not know the reason for the suggestion from wren not to use them, did you e-mail them? did you allow the turbine to continue the sequence to see if it will reach idle? did it? I can tell you I have seen that kind of behaviour whenever there happens the second step on the ramping stage and the starter has disengaged. What is your starter switch off RPM set at?(parameter 23 on a FADEC). Did you check that the pump is working? another reason could be that your are still running on gas only

I forgot to ask, is your battery really a ni-cad? are you sure it's not a ni-mh? I would understand them recommending not to use ni-mh batteries because of high internal resistance, anolther giveaway is the capacity, I could be wrong but I believe 3300's come only as ni-mh's

Hi Ruiz-Thank you for the reply. The battery I used is Nickel metal, not NiCad. Wren says to use NiCad-and not to use Nickel metal. The engine wont settle into an idle of 45K, it only gets to 22K. The parameters are all where Wren says they should be. I think the reason Wren says not to use nickel metal is the amperage isnt as great as say a NiCad or Lipo type. I have emailed Sara at Wren, but being Sunday I havnt received a reply yet.

Hi again Ruiz-the batt is nimh not nicad that wren says to use. I think, based on youre above statement that we are on the same page. Im thinking I need a 7.4 volt Lipo 1500mah to do the trick. Im thinkinking the reason wren says NOT to use nimh batts. is a lower amperage than nicad or lipo-

use a nicad or lipo, you'll be OK....

Yes indeed, thats what Im thinking too. Not enough juice (amperage) for successful start. ECU's likee de joos

A 3300nimh pack will have no problem supplying the amperage you need.
I use a 3700 pack on mine.

Before lipo's were around, we pulled 50+ amps from those packs flying fast edf's. I think Wren's policy addresses smaller, older generation packs from years ago.

If the pack is in good working order it will do the job...........


gregg

Sounds like an ECU issue. You are hanging up at the first fuel ramp point (where it switches from propane to kero). Have you changed any of the ramp paramenters? Make sure all the ramping parameters are where they should be (refer to your ECU instructions) My Wrens run fine on NiMh and Lipos. Scott

AT 22K RPM the starter motor should still be engaged and stay engaged up to 30K, but 400 degrees is very hot for that RPM...it shouldn't reach 400 until close to 40K

I'm thinking that the starter motor may be holding the turbine back - could be either the battery, motor, or bendix.

If it were mine (I'm saying that because I don't know if this is a recommended procedure)..I would try a dry start ...gas, but no fuel, to see if the starter motor will drive the turbine up to 30K, then cut out..

Use either a nicad or 2 cell lipo..... even a cheap 6 cell RC car pack is good for at least 2 flights.... Lipo's are even better!

Make sure the starter & glow plug wires are away from the RPM sensor wire, I just run them through the same grommet & had problems starting. - John.

The 3300 mAh Nimh should handle the approx 10 A that are being drawn on the start up . I use Nimh on all my Wrens and they work fine . There is the possibility that this particular battery is not delivering . Check the voltage of the pack under load . Also confirm that your autostart settings are in fact commanding the starter to at least 30k rpm . If the start was progressing on kero and hanging at 22k I would actually expect that the temps would start going high . Make sure that the engine is getting kerosene . No blocked filters , kinked lines and that the kerosene solenoid is plugged into the correct port if you're not using the propane solenoid ( I don't). Good luck !

Marc

After a night of restless sleep I got up and grabbed a cup of coffee and went out and stared at the engine. Thinking. And then I had a thought. What if I had crossed the gas and fuel lines? How would the engine act? So I pulled the front cover since the cover hides the feed lines. I got the cover off and VOILA!!!! CROSSED LINES

Marc-your post prompted me to check the lines!!!! Thank you sir!!

Kev

Life is good again ! Glad you got it fixed . It's certainly not the first time someone has done that and won't be the last ! Of course I've never done that ....

Marc

I'm sure you haven't Marc ... and I won't post here the names of people I know who HAVE done it, there isn't enough room and I can't afford to upset that many customers!

Well done, Keith, I'm glad you figured it out and the engine is running well now.

Sara Parish
wren Turbines

...'Been there, 'done that...........Didn't even get the t-shirt!

BTW, The new Ni-Mhs should be fine. They can certainly pump out the required amps. I switched from Ni-Cads to Li-Pos a while back. The only change that I saw was that I had to decrease the plug power to keep from blowing the glow plugs. I think that the Li-po had higher voltage under load and therefore the plug saw more juice than with the tired Ni-cads that I was using. I'm a little squeamish about charging the Li-po in the plane though. I only use it where I can easily remove the battery for charging.

Has anyone tried the A123 cells for the ECU?

I hope that this helps.

Tailwinds,

John

John,

Funny you should ask about the A123's . I fly electric as well and have been using these cells for almost a year now . I've used them in applications drawing almost 60 amps and they work really well .
Most recently I started using them for other applications . I use 2 2s packs for the RX/servos in my new Wren XL200 powered Liebetrau SU-27 . When tested with a 2A load the packs deliver 6.4v . Last night I did a test at 10 amps and still got 6.2V . I haven't tested the amp draw on start up for the turbines recently but did a test a long time ago on a RAM 500 and got only 8 amps . Next start on the XL I'll check . I'm sure the XL200 is a good candidate for 2S A123 because the starter off RPM is only 18k and theoretical no load speed on the Speed 280 BB starter motor is about 28 K at the 6.2 volts a 2s A123 pack would deliver.
While I'm sure it's suitable for the larger motor , a 2S pack may be marginal for an MW54 size motor and a 3S pack would be required for the MW 44 because they need to be spun up past 35k for good cool starts.
I love the fact that these cells are less critical than lipos and can be charged very quickly . I'll do some more testing over the next little while and post my findings here.

Marc

Interesting Marc. So, what is the nominal...no load voltage of the A123 cell? I heard it was 3.6 volts just like a Li-po. I wonder what the voltage under load is for a Li-po. I'm not sure, but I think that I measured the amps on my MK II autostart at around 10 amps when the starter and glow plug were running.................That's with the Speed 280 starter. I guess that the plug turns off prior to the fuel pump running and I don't have specific numbers for the pump-on and starter-on load...............

Tailwinds,

John

A123's are charged to 3.6-3.7 v /cell and settle down to approx. 3.45v/cell no load . Lipos are charged to exactly 4.2v/cell and pretty much stay there unloaded . Lipos will drop down to approx 3.6-3.7 v/cell under the light load of a starter/glowplug/pump. The pump itself only draws 1-2 A . The starter and glowplug present the harshest demand on the battery .
I have a data logger that I can hook up next time and get some real figures as the start progresses and then running to full power . Should be intertesting !

BTW if using a lower voltage pack , the voltage must be enough to spin up the motor to the required speed and the Low Batt warnings parameters in the FADEC may have to be changed.

Marc

i use a 6 cell 4000 ni-mh at 7.2mah on mt wren mw54 mk3 for the ecu and had no problems