Battery options - Rotax 912ULS

[Kyle Communications]

yes but it may as well be a boat anchor with their weight..they weigh about 9 or 11kg

 

 

[Thruster88]

5 minutes ago, Kyle Communications said:

yes but it may as well be a boat anchor with their weight..they weigh about 9 or 11kg

 

 

I just bought a full river hc20 for my RV6a because that is what it had, they weigh 6.6kg and have 325 CCA. How will a lithium type battery handle the big old style starter on a lycoming 0-360?  

[rgmwa]

PC680 weighs 7.0kg.  

[Kyle Communications]

They must have changed them..I used them years ago on 4WD comms systems...they were a hell of a lot heavier than any lead acid battery..they had a steel outer case

 

[RFguy]

yes, I agree with Mark--- you dont need a battery the size of a PC680 to start a Rotax. that's abotu 2x a big as you need

aim for a lead acid battery around 6kg.

 

One day Stuart we can put a clamp meter on your starter cable and measure the cranking current, and stall current. STuart my guess is the current might be about 1.5 the jab
the Jab is 1500W starter ,( so at 10V, thats 150amps. ) . I'd bet the starter isnt quite the ratio of cubic inches because you have four cylinder, I have a 6 cyl, more compressions per revolution.. at a guess, you, ahhhh  maybe about the same actually.  bit of extra power at the start- u have a heavy prop to swing.  

LIFEPO - Stu you'd want, I think at least a 150/4 = 38 AH you could go down to 150/5 but that's pushing it . again, all that capacity is not really useful except to keep your eelectroncis running in event of alternator generator failure. hence the god awful lead acid battery's   great cranking current does the job. .

Or a bank of NiCd batteries , which can go 50x C on discharge !

 

Edited August 6, 2021 by RFguy

[skippydiesel]

3 hours ago, rgmwa said:

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

 

Compare performance & weight, as well as the $$$ (didn't do a thorough search but the PC680 I found were in excess of $300).

 

Odyssey has the reputation as an aviation battery and the price to go with it. Your PC680 would seem, on paper, to have less performance and more weight than the SSB RB16CL-B.

[RFguy]

I wonder what people think of required run time in their aircraft for no generator ?

?????
Helicopters(real ones )  I used to associate with always ran NiCd batteries. Great starting batteries they are. 50C discharge  is possible without too much worry.

 IE I would be able to start the Jabiru on  10 D cells ......yes true....

...  cant say the same for NiMH. 

 

[Blueadventures]

On 04/08/2021 at 10:35 AM, 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/

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

I am using a Full River HC20 cca230 and 7 kG on my ULS2 912 for over a year all good.  Had an Oddessy  before that.

[rgmwa]

The Odyssey PC680 is the standard battery Van's supplies with the 912ULS for the RV-12, but they supply the much lighter Earth-X (0.6kg) with the RV-12iS because the engine is heavier. 

 

[IBob]

Unibat CBTX20CH-BS 12V18AH lead acid came with the kit, I've emailed for the spec, including weight. Works fine.

Located behind the pilot and could be further back as the Savannah S tends to run out of elevator authority on landing rollout.

 

Poor starting risks expensive damage to the 912 and good starting requires the engine to turn over briskly. So I fitted a battery negative cable (rather than relying on the aircraft hull), as others have done.

[skippydiesel]

Unibat Specifications

 

CBTX20CH-BS

Cranking power A/EN: 270 Ampere

Capacity AH (20hr): 18

Volt: 12

Weight: 4.26 kg

Acid volume: 0.82 litri

Regular charge current: 0.00 Ampere

Size (millimeter): 150 x 87 x 161

 

Nice and light but down on performance compared with the aforementioned SSB.

 

Not sure if available in Australia bit if it is, price competitive.

Edited August 7, 2021 by skippydiesel

[RFguy]

4.3kg is light for a lead acid.. ....Of 12V 18 AH. I'd b sceptical of capacity , but I am sure it owuld doo the craking job no problem.

 

This is the thing

QUESTION :  HOW MUCH RUN TIME ON BATTERY ONLY do people want ?

[Bruce Tuncks]

Thats a real hard question to answer: Enough time to start the engine, but that changes!

My Jabiru usually starts immediately, but once in the Flinders, when it had been out all night, it took forever to start and I was worried about the battery when it finally started.

I reckon it is best to have plenty of amp-hours there and if there is a weight problem, then a LiFe battery is best.

[Bruce Tuncks]

But do not be fooled by "lead-acid equivalent" amp-hours which means nothing except a rip-off.

[IBob]

2 hours ago, RFguy said:

4.3kg is light for a lead acid.. ....Of 12V 18 AH. I'd b sceptical of capacity , but I am sure it owuld doo the craking job no problem.

 

This is the thing

QUESTION :  HOW MUCH RUN TIME ON BATTERY ONLY do people want ?

Yep, probably a bit on the light side. It's classed as a motorcycle battery. My 912 starts first pop, so the battery has never really been 'tested'.

[RFguy]

all CCA rated  lead acids should do 30 seconds of cranking at the rated CCA  before they slow down . CCA has little  relationship to capacity, since it is related to the plate area.  and bear in mind, there is a thing called surface charge- essentially if the lead acid cranking slows, just wait half an hour, it will be good for a little more.

-about 60 seconds total (time spaced cranking ) that should be enough for any engine to start, if it is going to start.... 

-The thing is, the CCA is a rating for maintaining at least 7V at -18deg C. they'll do alot better than that at 20 deg C.

 

With LIFEPO, you will find the battery will crank at 12V at 4xC, whereas the lead acid at its specified CCA, will crank at room temp at only 9 volts.... so the starts are MUCH more lively with the LIFEPO, which might mean even more need to a soft-crank-start for the Jabiru. 

 

I think its time to build and sell some inline alternator charge limiter. something really simple.  

Which leaves the CG issue to deal with. I'd be happy to get 6kg out of the front of my J230D, (J230 fliers, you know what Im talking about) and move it elsewhere.

Other operators may rely on having that weight up the front for their plane to stay within limits. 

 

Currently I have plans for a 40AH LIFEPO4 behind the back seat in some sort of ammo box, fused and isolated at the battery. Got to figure best way to run it.

for 150 amps, 1 volt round trip drop, that's 6.6 milliohms. it would be about 0.5+1+1 = 2.5mx2 = 5m of wire, so the cross section needed is (.01726 / 6.6e-03 ) * 5m

= 13mm2.

quite a bit. 6AWG. but 6AWG doesnt have that current rating, 4AWG x 1 is OK but possible a pain due to size. and unlikely to find it easy in the Tevnel etc COTS aircraft wire.    You could run it as 3 lots of 10 AWG (or 4 x 12 AWG) going each direction and meet current ratings. You run pretty close to the wind with 3 x 10 or 4 x 12, so more likely 4 x 10 or 5 x 12. 

2 x 8 AWG would also be OK. 

 

 

 

 

 

 

Edited August 7, 2021 by RFguy

[skippydiesel]

2 hours ago, Bruce Tuncks said:

But do not be fooled by "lead-acid equivalent" amp-hours which means nothing except a rip-off.

You are quite likely correct, however without the means to put every prospective battery purchase through a series of tests (assuming that the vendor would let you)  most people (including me) just go by the published specifications , plus a fudge factor and hope for the best.

 

Just as a side note regarding published specifications: when I was refurbishing my aircraft fabric/skins the recommendation was to sue a domestic iron that would meet & hold a set temperature ? +/-. I spent hours in variose whitegoods stores, sitting on the floor with my thermocouple/meter,  by the iron display,  trying to find just one that would come close - none did. Purchased the biggest model aeroplane iron (with quite good digital read out,  that I could find - did the job well.

[Marty_d]

Ok, so I decided to get the info from the horse's mouth and asked Bert Flood's what they recommend.

 

The bloke there said Panasonic LC-XC1221P, which is a deep cycle battery (21AH).  So I rang around trying to source one, the shop whose national internet page offered them for sale told me that no, they'd talked to the supplier, and these are no longer produced.  In fact Panasonic only make 100AH and bigger now.

 

This battery shop bloke was very helpful.  Couldn't understand why Rotax would recommend a deep cycle battery for an engine starting application, said that a "cranking" battery would be better (talked about the different thicknesses of plates inside them - you guys would know a lot more about the differences than I do).  He ended up recommending the Full River HC-20 which apparently is a clone of the Odyssey pc680, mentioned above, but substantially cheaper as it comes from China instead of the US.

 

So I think I'll take the weight hit (7 - 7.5kg without the steel case) and get one of those, mount it behind my arse and there won't be any problems with overheating.  Will just have to lose that 5kg myself.

 

Thanks all!

[IBob]

Plus one for the cranking:

There is no electrical connection on the 912 between the battery and the ignition systems.

The electricity for the ignition is generated by coils in the stator as the engine rotates, and the engine must rotate at a sufficient speed for that to happen. So, to start well and reliably, the engine needs to rotate briskly.

[skippydiesel]

13 minutes ago, IBob said:

Plus one for the cranking:

There is no electrical connection on the 912 between the battery and the ignition systems.

The electricity for the ignition is generated by coils in the stator as the engine rotates, and the engine must rotate at a sufficient speed for that to happen. So, to start well and reliably, the engine needs to rotate briskly.

Agreed 110%

 

Hence the advise to purchase the, most cost effective, battery with the most cranking amps (taking into account weight & dimensions). Battery's designed for large capacity motorcycle starting, are your best contenders, being compact, light weight, vibration & spill resistant.

[tillmanr]

I recently replaced the battery in my Foxbat like for like with a Fusion 

CBC12V22AH. 6kg. The Rotax  is a 912 ULS 100HP

Bought it on eBay $84 delivered

[onetrack]

It's interesting to see that the Fusion CBC12V22AH battery is a VRLA deep-cycle battery - but it is approved and warranted for use as a starting battery.

So much for the repeated story we get, that there are deep-cycle batteries, and starter batteries, and you can't use one for the other. I keep hearing from people who are using deep-cycle batteries successfully as starter batteries.

 

https://www.batteriesdirect.com.au/shop/product/13283/Fusion AGM VRLA 12V 22Ah - Cyclic Use.html

[RFguy]

Marty, the battery guy gave you good Yep.,like I keep harping on about, its all about the cranking !

You can get a smaller ampere-hour (capacity) lead acid battery  than LIFEPO, or similar:

 

The HC20 sounds like the ticket...  for Rotax , or jabiru. Marty, I like it.

It is a trifle heavier than a PC625 8 versus 6kg, and that might affect CG (in the front probably nose heavies a bit more but you might want that.

 

http://www.fullriver.com/products/admin/upfile/HC20.pdf

 

Now, in LIFEPO,  assuming same weight, you'll get a 36AH battery, and probably good for 180 cranking, but  the difference is, you'd get 15 minutes of cranking capacity at 150 amps  (Jabiru 6 cyl) instead of 2 minutes (lead acid) . and you'll probably get 36 hours with just radios on instead of perhaps 10 hours.

 

Cranking speed of the LIFEPO is ferocious, because the battery will still put out 12V during cranking, where as the Lead Acid might be down the 9 volts..... (that can help you if you put your battery in the back with excessive Vd!) 

 

There's always a decision time, do I keep cranking (with rest periods) ? or do I try and sort the problem out early and then still have enough for cranking when I have turned the fuel on etc etc!

 

Edited August 14, 2021 by RFguy

[IBob]

An aside regarding the charging and trigger coils that provide the energy and the timing for the ignition: off topic, and has been mentioned before, but this seems like a good place to revisit it.

 

The gap between these coils and the trigger magnet cams on the flywheel is critical: too wide a gap has been seen to give poor starting, even with a well maintained engine and battery system.

This gap is given as 0.4 - 0.5mm (16 - 20 thou) for old type coils, 0.3 - 0.4mm (12 - 16 thou) for new type coils.

 

It is not hard to locate these fittings on the back of the engine, but the gotcha is this:

Because the feeler gauge is between the strong magnet of the cam and the coil, it will stick tightly to the cam, and feel like a good snug fit, even if it is not. Furthermore, when 'feeling' from the side' the feeler gauge has to be flexed to fit the gap, which also gives the illusion of a snug fit.

 

We found it easiest to use the brass feeler gauges which are part of some sets; also to remove (unscrew) the required gauge from the set to give better 'feel'.

In the absence of brass feeler gauges, it would be essential to ensure the next size up gauge was 'no-go'.

 

 

 

Edited August 14, 2021 by IBob

[RFguy]

I'd probably use the one -step smaller battery- the HC18, same size and weight  as the Odyssey PC625 in the Jab

 

https://batteriesdirect.com.au/shop/product/22727/fullriver-high-cranking-battery.html