What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

How many amps to open a starter contactor?

T

tonyjohnson

Well Known Member
I have my starter button on my stick which has a connector in the wiring cable that is limited to 3 amps. I have seen a wiring diagram that shows a 7amp fuse in the starter circuit.

Does anyone know how many amps it takes to activate the starter contactor?

Thanks,
Tony
 
Over 3 amps..

My Van's contactor measures 3.6 ohms. At a starting voltage of 12.5V nominal, it works out to a little over 3.4 amps. Sounds like your switch will be a bit light.

BTW. If you do go that way, put a switch on the panel to disable the starter button on the stick after starting. Too easy to hit it in flight.

Have fun,
John
 
I would suggest connecting it up with an amp meter and measuring it.

10 or 11 years ago, I measured the MASTER solenoid that Van's sells. It pulls 1 A at 13.8 Volts.

Remember that this is a COIL that you are completing the circuit with your switch. If I remember correctly, a coil will pull a surge of 10 times its steady state current draw. Also do not forget that the collapsing magnetic field will create a reverse current flow. In other words, there can be arcing on the switch contacts that will cause pits and eventual failure of the switch contacts.
 
Starter current

As a data point, I inadvertantly put a 5A fuse in instead of the 7.5A I planned on. It started fine 3 times, then blew the fuse the 4th time. 7.5A fuse in there now and it works fine... (using the B&C starter contactor and a 14V system)

John
RV-8 N94DW
 
I wired a relay to the momentary switch on an Infinity grip. This puts only a minimal load through the grip switch while the relay takes the contactor load. I didn't want to over load the momentary switch.

Jekyll
 
Jekyll said:
I wired a relay to the momentary switch on an Infinity grip. This puts only a minimal load through the grip switch while the relay takes the contactor load. I didn't want to over load the momentary switch.

Jekyll
Click to expand...

Jekyll,

I am using the radio shack relay to activate my boost pump from the switch on my infinity grip. I figure I could do the same thing with the starter circuit if I had to. From the responses to my question on this thread, it looks like I will indeed not be able to use the infinity start button without a relay. I appreciate the responses and very helpful information.

Which relay did you use? Do you know how many amps the relay pulls?

Tony
 
Last edited:
Just don't forget that all these little "dodads" adds to the number of possible failure modes in your systems. When it comes to airplanes it's a good idea to assume that everything IS going to fail, so the less things you have the less likely you are to have failures. Don't overengineer a simple system just because you can. And just my opinion but if you're using radio shack components for all this neat stuff in your plane you're really asking for trouble. They basically sell second rate components, or to be less politically correct, it's junk not fit for anything of any importance in an aircraft! Just my opinion take it or leave it.
Walt, 7A flying 500+
(A/P, Avioncis 25yrs+)
 
Good Point Walt!

Walt said:
Just don't forget that all these little "dodads" adds to the number of possible failure modes in your systems. When it comes to airplanes it's a good idea to assume that everything IS going to fail, so the less things you have the less likely you are to have failures. Don't overengineer a simple system just because you can.
Click to expand...

My personal, fundamental, design philosophy statement, permanently etched on my office wall...

"Perfection in design does not come when there is nothing left to add....but when there is nothing left to take away!"

Paul
 
Contactor current

I am presently wiring the contactors so I measured the current draw for both.

The start contactor draws 3.5 amps at 12.5 vdc.
Keep in mind the the actual number will be less as the starter pulls down the battery voltage. Example at 10 volts the draw will be 2.8 amps.

The battery contactor draws 720 ma at 12.5 vdc and 794 ma at 13.8 vdc.

I am using a Infinity grip with the start switch in the grip. I do not plan to use a relay as the switch is rated for 6 amps at 12 vdc and 40,000 operations.
With a spike diode on the contactor and less than 3 amps at the switch, I would believe the system should offer long term reliability without a relay.

Did I overlook something or is this thinking sound?

Don
Rv-7 Finish kit
 
Walt said:
Just don't forget that all these little "dodads" adds to the number of possible failure modes in your systems.

Walt,

I am sure that you are very happy with your non doodad airplane and your reasons for wanting that style airplane are sound. Personally, I like doodads. I understand the additional weight, expense, failure points etc. I am willing to accept those tradeoffs to have my doodads.

I intend to have fun in the design and build of my airplane. That is the beauty of an experimental aircraft, you make it what you want it to be, including doodads if you want them.

The only radio shack item that I have on my airplane is the boost pump relay. That is because it was the one recommended by infinity. I would consider a non Radio Shack alternative, expecially if the amps to open the relay were lower than the Radio Shack relay.
Click to expand...
 
RV6_flyer said:
I would suggest connecting it up with an amp meter and measuring it.

10 or 11 years ago, I measured the MASTER solenoid that Van's sells. It pulls 1 A at 13.8 Volts.

Remember that this is a COIL that you are completing the circuit with your switch. If I remember correctly, a coil will pull a surge of 10 times its steady state current draw. Also do not forget that the collapsing magnetic field will create a reverse current flow. In other words, there can be arcing on the switch contacts that will cause pits and eventual failure of the switch contacts.
Click to expand...
Gary,
I don't think this is true for a plain DC coil. I think that it is possible for an AC coil that depends on the drawn up armature to increase the reactance of the circuit to have a larger initial current surge. My brain is a bit crusty, though so you might be totally correct.

-mike
 
good information

Don,

Thanks for the information. That was exactly the kind of data that I was hoping to find here. It seems like you and I are both in the same boat, with one possible difference. My inline connector on the stick wiring cable is only good for 3 amps. If you do not have a connector, or if it is rated at a higher level than mine, you should have no problem.

I think there must be more about this issue that we are understanding. For example, Droopy reports that his starter circuit blew a 5 amp fuse. If your measurement of 3.5 amps draw is correct, you would not expect to blow a 5amp fuse.

Could that be because of the spikes associated with a contactor? Perhaps Droopy was using a different brand/type contactor that you are?
 
tonyjohnson said:
Jekyll,

I am using the radio shack relay to activate my boost pump from the switch on my infinity grip. I figure I could do the same thing with the starter circuit if I had to. From the responses to my question on this thread, it looks like I will indeed not be able to use the infinity start button without a relay. I appreciate the responses and very helpful information.

Which relay did you use? Do you know how many amps the relay pulls?

Tony
Click to expand...

Tony,

I used a Bosch relay from Waytekwire.com (P/N 0-332-209-150) but a 12 volt Napa relay would be the same.

I looked at my schematic again to make sure my memory was correct and found it to be only "sort of". I used the relay in my start circuit to select between the grips so I could enable or dissable the c/p grip. I designed it such that the pilot grip is the default if either power or the relay goes out. Of course, if power goes out, I don't really care which putton is connected to a dead circuit.

I talked with JD at Infinity about all this stuff last year and he stated he designed the start button wiring specifically to carry 6 amps to ensure the starter contactor could function properly through his grips. The starter button wires have larger wires than the other functions.

I regret I mistated the purpose of my relay.

Ironflight:

I agree with your premis but it must be tempered by mission requirements. There is a companion concept to your minimalist concept which I think is primal and that is to design fault-tolerant products. In my opinion, the hierarchy aligns something like this:
1. design into a system the capabilities that are needed to satisfy the mission objectives;
2. design fault tolerant systems to mitigate failures;
3. once 1 and 2 are obtained, apply the rule that if it ain't there it won't break.
I work in DoD weapon systems acquisition so I'm very familiar will R, M and S. The relays may fail but if my system is designed to be fault tolerant than the most the failure will cause is some maintenance time and money. My grip relays add complexity, cost and weight but I was more than happy to suffer those charachteristics to realize benefits I consider far more valuable:
1. be able to have my starter on the grip to provide what I consider a safety and security improvement and
2. be able to dissable the c/p starter button so my grandkids can't activate it in flight.
If any of my grip realys fail, control reverts to the pilot with the fuctions still operable. Fault tolerant.

Jekyll
 
Tony,

The current draws listed above are the stock Van's contactors.

A thought on your 3 amp limit, if you have any spare pins on your connector you could double up on the pins and raise the capacity.

RV6 Flyer
"Also do not forget that the collapsing magnetic field will create a reverse current flow. In other words, there can be arcing on the switch contacts that will cause pits and eventual failure of the switch contacts."

Some of you may remember the points and condenser used pre EI. The points would hold up very well under the collapsing magnetic field of the ig coil, but once the condenser failed the points were short lived.


Don
RV-7 Finish Kit
 
Last edited:
Clarifications and answers..

Lots of good stuff in the thread. Thoughts and replies here:

I think there must be more about this issue that we are understanding. For example, Droopy reports that his starter circuit blew a 5 amp fuse. If your measurement of 3.5 amps draw is correct, you would not expect to blow a 5amp fuse.

Could that be because of the spikes associated with a contactor? Perhaps Droopy was using a different brand/type contactor that you are?
Click to expand...
Different contactors and/or wiring setup. Spikes would not normally account for blown fuses.

Remember that this is a COIL that you are completing the circuit with your switch. If I remember correctly, a coil will pull a surge of 10 times its steady state current draw.
Click to expand...
Basic coils do not exhibit an inrush current. Quite the contrary, a coil (inductor) will resist current changes through them. Inrush currents are more likely to be found in loads like incandescent lamps (where the cold-hot resistance ratio is indeed about 10X) or capacitive loads (initial power up of electronics etc).

Also do not forget that the collapsing magnetic field will create a reverse current flow. In other words, there can be arcing on the switch contacts that will cause pits and eventual failure of the switch contacts.
Click to expand...
Absolutely true. Not only will arcing be a problem, transient voltages in the several hundred volts (about -450 volts in the case of the contactors :eek: ) can be generated. In these enlightened, microprocessed times, diodes across not only the contactors but ANY relay coil are a must.

And just my opinion but if you're using radio shack components for all this neat stuff in your plane you're really asking for trouble. They basically sell second rate components, or to be less politically correct, it's junk not fit for anything of any importance in an aircraft! Just my opinion take it or leave it.
Click to expand...
Absolutely agree. Why get your shorts in a wad over non-spec AN fittings AN Issues and then use hobby-junk in the electrix? Lots of better alternatives. Mouser. DigiKey, Allied, BC, Stein, Van's even. Lots.
A thought on your 3 amp limit, if you have any spare pins on your connector you could double up on the pins and raise the capacity.
Click to expand...
Be careful on this one. As the contact pairs age, they will inevitably exhibit different contact resistances causing one set to carry more than 1/2 the current. I know its common and you probably can get away with it with these low currents but its a bit iffy. You just don't know how normal contact wear will affect resistance and current draws between the two. Fixed connectors would be much less affected than switches but its a matter of degree that I'd rather not explore. (Actually, I HAVE explored.. with negative consequences).
"Perfection in design does not come when there is nothing left to add....but when there is nothing left to take away!"
Click to expand...
Don't overengineer a simple system just because you can.
Click to expand...
Possibly the best advice on the forum. What's not there weighs nothing and can't break. Before adding a relay, why not try to find a switch that will fit where you want it and carry the load?
Decreasing operating weight of 9A by
Removing lead from Pilot's derriere.
Currently @ 239 - a 42# improvement.
Click to expand...
My vote for best advice in the thread, Mike. I need to do it too. Rather than beating out the 8 x 2 1/4" holes in the steel battery box to save a louzy 4oz. of weight off the plane, spend the hour in the gym. GOOD JOB! Time for me to lay off the chips...
PS what's your target? May just have to get a little competition going here..
 
Last edited:
You must log in or register to reply here.
Back
Top