Battery options - Rotax 912ULS

[Marty_d]

Hi all,

 

While the weather is too cold for painting and fibreglass finishing, thought I'd get stuck into the electrics.

 

What is the best battery option for the 912? 

 

I think placement is going to be in the engine bay - the Zenith build pics show it behind the passenger seat but given mine is a 701/Sav hybrid, that's where the header tank is going.

 

Some folks are apparently using EarthX Lithium batteries, which according to their website 

http://www.earthxmotorsports.com.au/

are often recommended by Rotax and recreational aircraft companies like Sonex and Kitfox.  Apparently they have battery management systems to stop them exploding.  Anyone using those?  

 

Any and all comments appreciated on pros and cons - cost, weight, safety, cranking power (I believe 25 amps is recommended - is that right?) etc etc.

 

Thanks!

 

Cheers, Marty

[RFguy]

912 starter specification is 75 amps. Most lithium batteries are short term happy to provide 3C (3 x capacity) so a 20 to 25 amp hour battery is about  the size you want minimum

 

Regulator may need current limiting as an empty Lithium battery will drink like a thirsty horse and may overload the alternator charging circuit,

Mark Kyle can elaborate I am sure on the charging.

 

while you are there, ensure the system has a master battery isolator located adjacent to the battery. Not like the Jabiru where the full battery current goes through the firewall without fuses or isolation.

glen

 

 

 

 

[skippydiesel]

Been down this subject/conversation a heap of times :

 

I favour the SSB Powersport XR Series High Performance AGM Part Number RB16CL-B. Purchased min for $140, 29/08/2013  - still going strong.

 

Make sure all connections are tight and use good quality terminals & cables of the correct diameter for length (there are charts to help you with this eg http://www.enerdrive.com.au/wp-content/uploads/2015/04/Cable-Chart.pdf )

 

Technical Data

Part No	RB16CL-B
Volts	12
CCA	385
Reserve Capacity	-
Dimensions
Length	175mm
Width	100mm
Height	175.3mm
Terminal Height	160mm
Weight	6.6KG

 

AH (20hr)	19
Regular Charge	1.9
Max Charge	5.7
Plate Type	-
Separator Type	Absorbed Glass Mat

 

 

[IBob]

If fitting a battery isolator, you will then need to fit a the large electrolytic capacitor to the voltage regulator output.

 

The reason for this is that during normal running, the battery acts as a load to smooth the output of the regulator. If the electrics are switched off (and the battery isolated) for some reason with the engine still running, there is a the possibility of a large spike in the regulator voltage and damage to avionics etc. I think that's right............?

 

Can't remember capacitor spec, but mark Kyle has written about it here, he'll know.

[Kyle Communications]

The cap is in the Rotax manual as a "optional " part..it needs to be a std fit because of the crappy generator.

 

22,000 uF at 40V miniumum but 50 or 63 V would be better

 

Marty the 701 is basically a Savannah Classic. The battery I think from memory from them is behind the pilot seat. The fuel sump is behind the pax seat. The last thing you want is a battery on the engine side of the firewall where its is bloody hot. I think you will need the heavier style battery as the Classic and the 701 do tend to be a little tail heavy

 

 

[RFguy]

that cap....buy a 105degC rated capacitor.. or replace a 85degC cap every 100 hours. 

 

[Kyle Communications]

Glenn is correct always try to get the 105deg versions but they are hard to come by...mostly are 85deg

 

I just looked at Element 14 and they have some in stock...well not here but a week or so away in their stock overseas  Element14 order code  2835151

[Marty_d]

Thanks guys - I'm in the checkout at Element 14 now - while I have free delivery (the mounting bracket tipped it over $50) - is there anything else I should be getting at this point in time?

[RFguy]

Just to confuse you

I'd actually use 2 x 10,000uF, 40V ,  in parallel instead of 1 x 22,000 due to the high ripple current.

 

But 22,000uF is what people use and the hours are relatively low for them. 

 

and I dont know about the mounting- it is highly likely the mounting for TWO would be much more difficult than for ONE.

I can hear Mark saying "Glen don't complicate it ! " :-)

 

so yeah, just 1 x 22,000uF 40V or 50V. will be fine.

 

 

[IBob]

Breakers and switches?

I added one more of each to split out my Radio and Transponder.

And you'll need some sort of cap to go on the + terminal of that capacitor so it doesn't bite you. But that's easily made out of a piece of hose, if need be.

[Kyle Communications]

I prefer the 63V after seeing how big the spikes come out of the generator and its easier to mount than 2 of the others

You can easily make a clamp mount out of 1mm alu

Breakers from element14 maybe a bit expensive..they have nice name brand ones but they are very good

 

[Guy s]

10 hours ago, Marty_d said:

Hi all,

 

While the weather is too cold for painting and fibreglass finishing, thought I'd get stuck into the electrics.

 

What is the best battery option for the 912? 

 

I think placement is going to be in the engine bay - the Zenith build pics show it behind the passenger seat but given mine is a 701/Sav hybrid, that's where the header tank is going.

 

Some folks are apparently using EarthX Lithium batteries, which according to their website 

http://www.earthxmotorsports.com.au/

 

Hi Marty, 

                  I replaced the bolly prop with a E-prop and the E-prop being half the weight of the bolly, and to offset this i replace my 5yr old lead batt with a EarthX battery with weights only 1.9kgs. I've done about 30hrs since and can't fault either.  

 

[Marty_d]

1 hour ago, Guy s said:

Hi Marty, 

                  I replaced the bolly prop with a E-prop and the E-prop being half the weight of the bolly, and to offset this i replace my 5yr old lead batt with a EarthX battery with weights only 1.9kgs. I've done about 30hrs since and can't fault either.  

 

Thanks, Guy.  Which model EarthX did you get?

[Marty_d]

5 hours ago, Kyle Communications said:

The cap is in the Rotax manual as a "optional " part..it needs to be a std fit because of the crappy generator.

 

22,000 uF at 40V miniumum but 50 or 63 V would be better

 

Marty the 701 is basically a Savannah Classic. The battery I think from memory from them is behind the pilot seat. The fuel sump is behind the pax seat. The last thing you want is a battery on the engine side of the firewall where its is bloody hot. I think you will need the heavier style battery as the Classic and the 701 do tend to be a little tail heavy

 

 

 

This stuff is complicated.  I've never done any wiring before except for a power point or light fitting.  From everything I'm reading it appears that the battery has to go straight to the starter relay (without switch or fuse between) because the starter motor can pull huge amps when turning over.  

So how is the capacitor wired to the regulator?  

Thanks for your patience guys - I am a total newbie when it comes to electrical stuff.  Making wing ribs is child's play compared to this.

[IBob]

The battery + goes to one terminal of the starter solenoid. That's the fat red cable.

The output of the voltage regulator (B on the regulator) that keeps the battery charged goes to the the same terminal on the starter solenoid.

Make up a short cable with lugs on the ends, and connect the + side of the capacitor to that same terminal on the starter solenoid.

Make up another short cable with lugs and connect the - side of the capacitor to your negative bus point.

 

The usual place for the capacitor in the Sav is at the RH end of the front shelf that carries the throttle bar etc. Best wait until you have the throttle bar etc in place, on the Sav there's not much room there.

 

[Guy s]

Marty I got the ETX680

[Marty_d]

Weight vs money by the looks of it....

 

The two recommendations so far:

 

SSB Powersport XR Series High Performance AGM Part Number RB16CL-B:    6.6kg     $154 delivered

EarthX ETX680:   1.86kg      $690 delivered

 

So one is almost 5kg lighter but over $500 more expensive.  If Skippy's is from 2013 that's 8 years, so no difference in longevity.

[skippydiesel]

The unspoken additional factor Marty - is the compatibility of your charging system.

 

There are many others on this Forum much better qualified than I on this subject.

 

I deliberately chose the conservative path when selecting a "conventional" lead acid batter - I just got  paranoid/confused about the newer (lighter) alternatives.

 

One other point I would make - the SSB I use,  is very much lighter than the original (lower powered) battery, that was in my aircraft when I purchased it - so from my perspective I have a win win, lighter battery, better cranking (possibly longer service life) without any changes to my charging system or safety concerns.

Edited August 5, 2021 by skippydiesel

[RFguy]

I think $680 is 5 x too much  for a 12AH battery LIFEPO4

The manufacturer is laughing all the way to the bank

I mean you got to be kidding that is a huge rip off in my opinion !

and you dont need BMS for those small LIFEPO4 battteries, in my opinion. You're not going to over discharge it by leaving the lights on, are you !?

 

Edited August 5, 2021 by RFguy

[RFguy]

try this one. I know these guys well.

https://www.ev-power.com.au/product/bat-evh12v20ah/

 

AUD$220 , free shipping out of Perth. 20AH (not 12AH like that other joke)

 

You'll note maximum discharge currents for LIFEPO as about 2C (2 times the capacity) . That's what ti has to be for the full battery life. In practice, 4x is OK for a short period.

 

That is probably fine for a 912ULS. (72A).

For the 4 or 6 cylinder jabiru, I think you want a bit more, especially the 6 cylinder (125A, 12V ), I'd be going for 32+ Ah battery only because I'd be observing the < 4C rating.

Although people torture these batteries all the time, .. no problem at all. 

 

this is the  thing---. lead acid batteries make excellent starting current batteries. everything else, they suck at.

and so, 

I would probably choose the SSB Powersport XR  $160 , and replace it every couple of years.....UNLESS I needed to lose weight  in the airplane or change the CG

 

 

 

 

 

 

 

Edited August 5, 2021 by RFguy

[Marty_d]

Being a tightarse, I'm leaning towards the lead acid.  As my wife said, I could lose 5kg to make up for the battery. 

 

(Notice she didn't volunteer...)

 

 

Edited August 5, 2021 by Marty_d

[IBob]

Definitely put the battery behind you: it'll help with low speed elevator authority on rollout.

[RFguy]

Well, I looked up a few papers on the subject of max discharge rate for of LIFEPO4, selected the best graphs.

Now remember this is CYCLE LIFE - But we dont cycle these batteries (charge- deep discharge etc) . Use of these is more like useful for NiCd or PbSO4.

you can see at 4C, you are down to 750 cycles. You are NEVER going to do that in your aircraft. so dont worry.

 

here is some data on how the batteries look at discharge time- top one, FRESH, bottom one- at capacity loss of 20% (per first graph).

The 4C and 5C discharge curves show significant drop once the battery is aged by the hard work at 4C and 5C

(it is still much better than a new lead acid battery !)

 

 

 

Edited August 5, 2021 by RFguy

[skippydiesel]

11 hours ago, RFguy said:

try this one. I know these guys well.

https://www.ev-power.com.au/product/bat-evh12v20ah/

......................................................

I would probably choose the SSB Powersport XR  $160 , and replace it every couple of years.....UNLESS I needed to lose weight  in the airplane or change the CG

 

 

Every two years???? - I respect your much deeper understanding of these things than I have BUT I work on the basis of experience - that is to say when I get a hint of reduced cranking capacity (usually in winter) - I first give the battery a chance, by giving it an over night charge - No second chance, replace if that does not have the desired effect. This way you get the most service  life out of your expensive consumable/battery.

I learnt the hard way, that low cranking performance, may still start your Rotax but will almost certainly result in a replacement Sprag Clutch and lots of $$$ out of the pocket.

[rgmwa]

I use an Odyssey PC680 AGM with my 912ULS. It's about $160-$190 from various retailers.