Battery options - Rotax 912ULS

[Bruce Tuncks]

I started with 2 hobbyking LiFe batteries in parallel. They are 8.4 amp-hour 30C, which apparently means that they can provide 252 amps. They weighed just under a kg each, so the 2 were 2kg.

Well I thought I was going to damage the starter motor, so fast did it spin over, so I took one out and it is more normal, with the 6kg down to 1kg.

The old 6kg Odyssey went for another ten years on a farm buggy, but alas  it has had it now.

 

[Bruce Tuncks]

I should have worried about the flywheel bolts I now know.

[Bruce Tuncks]

The Jabiru kit came with a motorbike lead-acid Marty. It was no good at all. Even Jabiru moved to Odyssey batteries. I reckon the LiFe are much better and the weight saving is good too. Yes, I too could lose 5kg off my gut but it doesn't seem to happen.

The original motorbike battery was stuffed up by leaving it on a small camping solar charger for some weeks. It hardly turned the engine when I finally tried to use it. Yes, the solar charger had a diode which prevented night time discharge, so I don't really understand what went wrong. The battery did not boil dry either.

[Old Koreelah]

15 minutes ago, Bruce Tuncks said:

I should have worried about the flywheel bolts I now know.

 My Lithium turns the engine painfully slowly, then gradually speeds up as it warms. Gentle on the flywheel bolts.

Restarting when warm is not. Almost instantly fires, no doubt putting enormous loads on those bolts. 

Mine has dowels, so I’m less stressed, but should soon check bolt tension.

 

[RFguy]

I have a good  softstart kit sorted. and simple . but its using a part I only had one off and more are 6-10 weeks away, I will buy more.

 

BRUCE- BTW the engine in my aircraft 

a 2010 J230D, was replaced in 2013 with the new last gen3 I have now (that I also rebuilt)

you know why they had to replace it - in the field, flying, the flywheel fell of in flight......

 

they landed on a road (they were flying along) out western QLD without issue. 

Edited September 13, 2021 by RFguy

[facthunter]

It would have made considerable noise and probably vibration before that happened. Always investigate anything unusual. Engines never fix themselves. I've heard flywheels loose on cars and you can't miss it admitted they are heavier and more of a clunk  With the prop on one end and a flywheel on the other it's not an ideal set up .Nev

[danny_galaga]

On 14/09/2021 at 8:41 AM, Bruce Tuncks said:

I started with 2 hobbyking LiFe batteries in parallel. They are 8.4 amp-hour 30C, which apparently means that they can provide 252 amps. They weighed just under a kg each, so the 2 were 2kg.

Well I thought I was going to damage the starter motor, so fast did it spin over, so I took one out and it is more normal, with the 6kg down to 1kg.

The old 6kg Odyssey went for another ten years on a farm buggy, but alas  it has had it now.

 

If the voltage of your battery pack is about the same as the original battery (I guess 12V) I wouldn't worry about it. The faster the starter spins, the better. It's normally when they are spinning slowly they get damaged. Eg trying to start with a half dead battery. That's because the slower it is spinning, the more current it draws. It's why we could convert old 6V car systems to 12V without changing the starter or wipers. 

 

Zero rpm being almost a dead short and The faster it spins, the more back EMF it produces, the less current it draws. infinite RPM would be zero current draw.

 

In fact if your starter is spinning slower with just that one battery, I would say the battery is struggling

Edited September 17, 2021 by danny_galaga

[Bruce Tuncks]

Thanks Danny. The batteries are a bit different in that the LiFe is 13.2 volts, charging should cease at 14.2 volts.

It sure doesn't feel like it is struggling, and the motor starts immediately.

You sure know more electrical stuff than I do though.

Actually, that Jabiru was yesterday replaced with a Jab 230 D. This Jab has a big Odyssey battery in it as well as a Camit engine.

One of the things I will do one day will be to replace the Odyssey with a LiFe, but there are other things to do first, like the CHT's.

I have put my worry about this on another thread...

[danny_galaga]

1 hour ago, Bruce Tuncks said:

Thanks Danny. The batteries are a bit different in that the LiFe is 13.2 volts, charging should cease at 14.2 volts.

It sure doesn't feel like it is struggling, and the motor starts immediately.

You sure know more electrical stuff than I do though.

Actually, that Jabiru was yesterday replaced with a Jab 230 D. This Jab has a big Odyssey battery in it as well as a Camit engine.

One of the things I will do one day will be to replace the Odyssey with a LiFe, but there are other things to do first, like the CHT's.

I have put my worry about this on another thread...

Yeah, sounds like its ok. I didn't know the exact voltage. Seeing as it's about .8V higher than a lead acid to start with, what I imagine was a 'struggle' was still spinning faster than the lead acid battery! How long have you had this setup? That is a great weight savings!

[Bruce Tuncks]

For about 4 years now Danny. I did ruin a LiFe by leaving to master on while parked for a week. The cells gassed and the battery burst open. The terminal voltage was zero and it would not take a charge. So 2 years from an individual battery is my best. I hope the current one lasts longer though than the 2 years so far.

Those LiFe batteries are more fragile in some ways , you need to keep the terminal voltage between certain limits, more than the lead acid types. ( the old Odyssey was left to go to zero volts too, but it came good again on charging and served for another 4 years on a farm buggy)

But as you say, the weight saving with the LiFe  batteries is great. I am surprised that anybody who understands about weight and aircraft has not changed away from lead-acid.

[RFguy]

14.4  is the highest you want to charge them. 14.8 if you have active balancing and it's not forever.

14 is a good number to not float them above. 

[danny_galaga]

11 hours ago, Bruce Tuncks said:

For about 4 years now Danny. I did ruin a LiFe by leaving to master on while parked for a week. The cells gassed and the battery burst open. The terminal voltage was zero and it would not take a charge. So 2 years from an individual battery is my best. I hope the current one lasts longer though than the 2 years so far.

Those LiFe batteries are more fragile in some ways , you need to keep the terminal voltage between certain limits, more than the lead acid types. ( the old Odyssey was left to go to zero volts too, but it came good again on charging and served for another 4 years on a farm buggy)

But as you say, the weight saving with the LiFe  batteries is great. I am surprised that anybody who understands about weight and aircraft has not changed away from lead-acid.

For my kit build im using the lead acid battery supplied. I don't want to change anything because it's taking long enough as it is too build 😄

Edited September 19, 2021 by danny_galaga

[Marty_d]

3 hours ago, danny_galaga said:

For my kit build im using the lead acid battery supplied. I don't want to change anything because it's taking long enough as it is too build 😄

Try about 12 years to get where I am now... mind you I did have to fabricate everything myself.  I was hoping to finish by the time I hit 50 which leaves me about 7 months - don't think I'm going to make it!

[danny_galaga]

15 minutes ago, Marty_d said:

Try about 12 years to get where I am now... mind you I did have to fabricate everything myself.  I was hoping to finish by the time I hit 50 which leaves me about 7 months - don't think I'm going to make it!

You can do it!

[Kyle Communications]

When I bought Mabel I thought about 12 months to do the repair/rebuild...hahahahha yeah right..its turned out to be complete rebuild. I only bought the rear fuseage frames and firewall from ICP the rest I made like Marty has....So I know what he has done so far. I like to think I am reaosnably fast when it comes to this stuff and I have the advantage of access to some great metal working machinery and its taken me almost 5 years so far...so Marty dont feel in any way under done...you have done a spectacular job