Electric Pre-Rotator

Jazzenjohn

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I've designed, built, and flown 4 different ultralight gyros. Amassing parts for a 2 place now.
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First thing Dar, that's a great video! You are certainly very knowledgeable about these packs! If anyone can get Cylindrical cells to work, you'd be that guy. The issue I see on the packs is this, The connectors between the cells seem to be more than just a simple connection, they also appear to function as fusable links, and really aren't up to the current demands you are placing on them. I believe you'd have better luck with parallel packs as opposed to 5 ah packs because you are effectively doubling the current capacity of of the wiring when using 2 (or more) separate packs in parallel rather than using a single 5 ah pack which would have the same current capacity as a 2.5 ah pack due to the fact that the 5 ah pack would have the full current going through the same single foil to output wire connection where with 2 packs they would share the load at that point. You are obviously pretty adept with those packs and may have a different opinion about them. I have almost no experience with them myself, other than to overload a couple of them in the past.
 

Jazzenjohn

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I've designed, built, and flown 4 different ultralight gyros. Amassing parts for a 2 place now.
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On that video he said they were Sanyo 20 amp rated cells. That would suggest you might need several packs in parallel to get the full output of the Amp Flow motor. Maybe as many as 3- 4 in parallel, although he doesn't say whether 20 Amps is a short duration or long duration discharge rating. If they are the UR18650NSX cells, they show an output rate at 25 amps for full discharge so they might be good for 40 amps for 10 seconds or so maybe more? Mike has measured peak current draws on his motor as high as 250+ amps!
 

Jean Claude

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Here, Sanyo's characteristics for this cells:
  • Typical capacity: 2600mAh
  • Minimum capacity: 2500mAh
  • Nominal voltage: 3.6V
  • Standard discharge: CC/CV, 0.2C, 3V
  • End-of-charge voltage: 4.2V +/0.05V
  • End-of-charge current: 0.02C (50mA)
  • End-of-discharge voltage: 2.5V
  • Continuous maximum charge current: 1C, 2500mA
  • Maximum pulse charge current: 1C, 2500mA
  • Continuous maximum discharge current: 20000mA 7.5C or 22000mA 8.5C with temperature cut-off at 80°C)
  • Max discharge current vs. time: 25-30A > 30second, 35A > 15seconds, 50A -> 6seconds
  • Cycle life at 0.5C: 300 cycles to 80%
  • Initial impedance: 35mOhm

Very insufficient for a prerotator, because if you need of 2.5 kW and 36 volts, then it is 70 Amp. (ie less 6seconds). And when70 A, then the voltage of your pack of 10 cells gives: 36v - (10*.035 ohm *70A) = 12 v instead 36 v . Sad laws of electricity!
 
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Jean Claude

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Dar, That's better, but it's still not enough. Each double cell will have a resistance of .035/2 = .017 ohm, and the 20 pack will give
36v - (10*0.017*70) = 24 v
Each cell will have to provide 35 A (hence 15 seconds max)
This will give 840 w 15 secondes max.
While it would take 2,500 w for 40 secondes.

This cells is not designed for the high electrical power required.

PS I hope you'll forgive for my bad English, which you certainly find too rough. That is not my intention.
 
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okaneco1

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jm-urbani

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Hi JC,

how did U find out the internal resistance ?
was it specified in the the specs of the bat ?
As for Dar dow pack limitation I had come to the same conclusions then yours ( dar dow I had sent you a MP that I don't know if you eventually got it)

as for me, I will do my tests in the same conditions then jean F (who has calculated all for me) is doing his own tests

we are both using four 60C 5000 M/amp lipos packs ( 2S/2P)

but it won't be rechargeable in flight because of the fire hazard.

in the future if the first tests are satisfactory the goal is to use a pack made from A123 cells (Li phosphate) that will have a smaller C rate ( but enough the make the job)

the idea is to rely on the difference btw the continuous and max discharge rate and the burst but limited in time max dischare rate ( as you are saying)

A123 photphate cells have a lower continous max discharge rate but a descent burst max discharge rate.

if piloted accurately in time with the help of a microcontroller, the pre-spin time could be reduced in time down to 25 seconds not to exceed the max discharge rate time .

using A123 cells would allow us the install a safe recharging bms

then the lithium pack could be recharged by the rotax generator (very smoothly) and the pack could also provide the energy in order to stard the rotax and provide current to run the electrical system of the gyro

this was we could imagine that the pack would be sized for one or 2 pres-pin sessions and it would take 20 minutes on flight for the rotax to recharge it for an other pre-spin session ( a closed loop if you prefer)

I have caculated with my limited habilities that 3 kilos of cell would be enough to run the system (perette et le pot au lait)

bonne journée


thx
 
Last edited:

dinoa

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I also noticed 300 charge cycles at 0.2C. Doesn't seem like much life for those batteries at the max 30-45 second discharge rate
 

N7WWK

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Mar 29, 2020
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Fl
Looks your going in the right direction. Not sure of motor your using but may want to look at ebike battery pack 53volts running 1000- 1500 watt motors for up to 20 miles. High current output, for good duration.

Keep going!
 

Jean Claude

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I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C
Total Flight Time
About 500 h (FW + ultra light)
How did U find out the internal resistance ?
was it specified in the the specs of the bat ?
Yes, It was an information from the manufacturer PANASONIC- SANYO. But unfortunately, I can't find the site anymore.
 

Jazzenjohn

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When I suggested the cells were Sanyo/Panasonic UR18650NSX, I was just giving an educated guess based on the manufacturer, ah rating, cell color, size, and use.
 

Jazzenjohn

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That has poorer specs that the NSX cells and only rates it at 10 c output with one test cell failing at 15 c. 10 c is 23 amps and the official spec is 20 amps. I believe the motor will draw far in excess of 80 amps Peak. You can wait for Jean Claude to give you the math, or you can look at 80-100 amps, 4-5 packs in parallel, as a ballpark estimate of what will be needed to get close to the motor potential. In the end you may be satisfied with less than the full potential of the motor anyway. You can simply add packs in parallel until you get there. I have the impression you have a closet full of them and adding more packs isn't much of an issue, am I correct? If not, and you're buying them, I suggest you re-read posts 196, 203, 206 and 209.
( @JC looking at the test graph, it's showing the internal resistance around 53 mohms )
 
Last edited:

wolfy

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Dec 19, 2013
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western australia
Hi JC,

how did U find out the internal resistance ?
was it specified in the the specs of the bat ?
As for Dar dow pack limitation I had come to the same conclusions then yours ( dar dow I had sent you a MP that I don't know if you eventually got it)

as for me, I will do my tests in the same conditions then jean F (who has calculated all for me) is doing his own tests

we are both using four 60C 5000 M/amp lipos packs ( 2S/2P)

but it won't be rechargeable in flight because of the fire hazard.

in the future if the first tests are satisfactory the goal is to use a pack made from A123 cells (Li phosphate) that will have a smaller C rate ( but enough the make the job)

the idea is to rely on the difference btw the continuous and max discharge rate and the burst but limited in time max dischare rate ( as you are saying)

A123 photphate cells have a lower continous max discharge rate but a descent burst max discharge rate.

if piloted accurately in time with the help of a microcontroller, the pre-spin time could be reduced in time down to 25 seconds not to exceed the max discharge rate time .

using A123 cells would allow us the install a safe recharging bms

then the lithium pack could be recharged by the rotax generator (very smoothly) and the pack could also provide the energy in order to stard the rotax and provide current to run the electrical system of the gyro

this was we could imagine that the pack would be sized for one or 2 pres-pin sessions and it would take 20 minutes on flight for the rotax to recharge it for an other pre-spin session ( a closed loop if you prefer)

I have caculated with my limited habilities that 3 kilos of cell would be enough to run the system (perette et le pot au lait)

bonne journée


thx
Very interested in the Li phosphate battery idea Jm, looking forward to see how your testing go's.

wolfy
 

Jean Claude

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I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C
Total Flight Time
About 500 h (FW + ultra light)
looking at the test graph, it's showing the internal resistance around 53 mohms
John,
35 mOhms is probably a typical value after average lifetime.
But according these graph, I get about 20 mOms for the tested battery.

Sans titre3.png
 

Jazzenjohn

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Total Flight Time
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When I wrote post 214, the cell in post 213 was listed as the Sanyo UR18650ZL2. Post 213 has since changed to the cell I originally suggested it might be, the Sanyo UR18650NSX. If nothing else, it highlights the huge differences in similar looking cells and the fact that buying packs for use in applications like this is a grab bag, you won't know what's inside until you break it open. There is no real assurance that the cells will stay the same pack to pack either. https://www.candlepowerforums.com/v...Test-review-of-Sanyo-UR18650ZL2-2310mAh-(Red)
 

mvadney

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Aug 8, 2004
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Arlington
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Sportcopter Vortex
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Hello all.
I'm real sorry about not sending the photos that I have of my prerotator. As John said, I don't post much here. Just pure laziness.
Here are some photos of my newly rebuilt prerotator setup for my Vortex. I switched to a beefier controller (Kelly KDS controller) and a bigger, but the same weight battery. When I bumped the voltage up from 24v to 40v I popped my Vyper controller. It can handle up to 250 amps, but voltage is voltage. It was just too much. The 24v setup was only good for an honest 130-140rpm. VortexPrerotator1.jpgHopefully I can upload the pics this time correctly.
 

mvadney

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Arlington
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Sportcopter Vortex
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What do you know, I'm now a posting person. Wonders never cease.
Here is the controller that I used and the greatly abbreviated and proven wiring diagram that I use. The company use to be American, but was bough out by China some years ago. The help on the controller was very good and patient with me. It can use hall-effect or a simple Pot like the 10K one that I used.
KellyController.gif
 
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