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Starter Selenoid, Big Capacitor, Aux Fuel tank

PostPosted: Tue Mar 29, 2016 6:30 pm
by jjacky
Ok I'm going to be sorry I asked these questions because there are probably totally obvious answers but what the heck.

1. For a Rotax engine, with the starter connections just inches from the firewall, why is the standard starter solenoid (relay) located in the engine compartment? Seems like if it is locate it on the cabin side of the firewall you could get away with a single firewall penetration which would only be "hot" when starting the engine.

2. I notice that a lot people locate that big capacitor in the engine compartment. Is there a compelling reason for this?

3. I'm going to use a lithium ion battery which weights ...what...maybe a few pounds. So i need to get some ballast back where the original lead acid battery was. I'm toying with the idea of a aux fuel tank...Thoughts.

Please square me away....Thanks! ;>)

Re: Starter Selenoid, Big Capacitor, Aux Fuel tank

PostPosted: Tue Mar 29, 2016 10:55 pm
by SuperFly
J,


I put the rotax solenoid on the inside of the firewall for that very reason. Seemed silly to me to run that big wire through the firewall and have it hot all the time. Also mounted the capacitor inside, behind the panel along with a few other relays and stuff.

As for the battery, I mounted and EarthEx battery under the passenger seat, and put no extra ballast in the rear. I am very happy with the way it flies, and the weight and balance came out well within the specified range.

Re: Starter Selenoid, Big Capacitor, Aux Fuel tank

PostPosted: Tue Mar 29, 2016 11:18 pm
by FlyerChief
I'll take a stab at it...

1. For a Rotax engine, with the starter connections just inches from the firewall, why is the standard starter solenoid (relay) located in the engine compartment? Seems like if it is locate it on the cabin side of the firewall you could get away with a single firewall penetration which would only be "hot" when starting the engine.

Because you need a 12 volt supply for the voltage regulator module, it makes sense to have the relay firewall forward. You can tie into the hot terminal for your supply to the regulator. I guess theoretically, you could place the relay on the inside and run a smaller lead out to the regulator.

2. I notice that a lot people locate that big capacitor in the engine compartment. Is there a compelling reason for this?

There are actually two large capacitors required on the Rotax if you have an auxillary fuel pump. One is across the pump and the other goes across a couple of the terminals on the voltage regulator. Both reduce radio and other electrical interference and noise by smoothing out any voltage spikes created by those devices.

3. I'm going to use a lithium ion battery which weights ...what...maybe a few pounds. So i need to get some ballast back where the original lead acid battery was. I'm toying with the idea of a aux fuel tank...Thoughts.

The old saying is that you can never have to much fuel unless you're on fire, and it certainly can be useful weight, but one caution is that it may change your CG enough to be a problem when the tank is empty. If you find yourself doing a forced approach due to low fuel, your CG may have moved forward at the very time you need to be more tail heavy. Just something to consider when you plan where to put things that change weight as you fly. (That's why wing tanks work so well for maintaining a useful W&B over a large range... CG hardly changes from full to empty.) If you never run out of fuel, it shouldn't be an issue though.

Dan

Re: Starter Selenoid, Big Capacitor, Aux Fuel tank

PostPosted: Sat Apr 09, 2016 10:31 pm
by ja30driver
Think 2x about a lithium ion battery "inside" the cabin.
If it fails... Like mine did... It can be a mess... Bad mess!
Mount it forward of the firewall and away from fuel & brake lines.
Header tank behind seats (2 gallon)... Could be your answer.

Re: Starter Selenoid, Big Capacitor, Aux Fuel tank

PostPosted: Sun Apr 10, 2016 3:03 pm
by FlyerChief
ja30driver,
Tell us more about the lithium battery problem you had. There are a lot of stories about older technology lithium batteries that have caught fire, but little on the newer ones.
What make and model of battery did you have. Where was it mounted and how? Was there ventilation or was it enclosed? Do you have a photo of the installation and of the mess you mentioned? Do you think there were circumstances leading up to the problem or do you think it's just bad engineering or battery technology?
I suspect that I'm not the only one really looking forward to knowing more about what happened and why!
Thanks,
Dan

Re: Starter Selenoid, Big Capacitor, Aux Fuel tank

PostPosted: Sun Apr 10, 2016 4:41 pm
by gkremers
I would also like to know the manufacturer and battery type/model you had issues with.

I have an aero lithium battery and have never had an issue is 2 years. They do recommend using the balancing charger ever 40 hours do keep the cells consistent. Aero Lithium was the first company to introduce the lithium Iron battery technology to the aviation market approx 4 years ago.

It's amazing the cranking power these little batteries have.

Gary

http://www.aerolithium.com