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resistance in solenoid

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bobnoffs

Joined: 04 Jul 2012
Posts: 136
Location: northern wi.

Posted: Mon Dec 01, 2025 6:59 am Post subject: resistance in solenoid

my voltage number is dropping in my eis. i have determined it is resistance in my continuous solenoid for my battery. this solenoid is from acs and has only 100 hrs on it. i really dont want to redo those fat wires on the firewall to fit a different solenoid but isn't 100 hrs a short lifespan? should a go for a better solenoid?

 bob noffs

user9253

Joined: 28 Mar 2008
Posts: 1947
Location: Riley TWP Michigan

Posted: Mon Dec 01, 2025 7:53 am Post subject: Re: resistance in solenoid

Bob, does the engine crank and start okay?  If so, then maybe the solenoid is 

good.  Once the engine is running, the aircraft electrical system is powered by 

the alternator, not the battery.  If the EIS is showing low voltage with the 

engine running, suspect the charging system.

  The best way to measure low values of resistance is with a voltmeter and 

heavy load, not with an ohmmeter.

_________________
Joe Gores

jluckey(at)pacbell.net
Guest

Posted: Mon Dec 01, 2025 10:36 am Post subject: resistance in solenoid

Bob,

Assuming you are using the standard and ubiquitous solenoid like the Cole Hersee 24059, it should certainly last more than 100 hrs.  More like 10++ years.

JoeG is right on the nose with his advice.

Maybe you could post bus voltage with engine off and voltage with engine running.  Also have you confirmed the EFIS numbers with a volt meter?





-Jeff



                  

                                                                        On Monday, December 1, 2025 at 10:25:38 AM PST, bobnoffs <icubob(at)gmail.com> wrote:                     

                     



                     



                                                   --> AeroElectric-List message posted by: "bobnoffs" <icubob(at)gmail.com (icubob(at)gmail.com)>



my voltage number is dropping in my eis. i have determined it is resistance in my continuous solenoid for my battery. this solenoid is from acs and has only 100 hrs on it. i really dont want to redo those fat wires on the firewall to fit a different solenoid but isn't 100 hrs a short lifespan? should a go for a better solenoid?



 bob noffs



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bobnoffs

Joined: 04 Jul 2012
Posts: 136
Location: northern wi.

Posted: Mon Dec 01, 2025 3:37 pm Post subject: Re: resistance in solenoid

voltage at eis is 12.6 with engine off. it is 14.3 with engine running. i have checked all numbers with eis voltage, handheld voltmeter and panel mounted voltmeter i just bought and they are all aligned.. measured voltage is 13.2 at battery side of solenoid and 12.6 on the load side, engine off.  alternator is charging fine and battery voltage is fine but after the solenoid it drops to 12.6. all this is with an earthx, not lead acid.

 i haven't actually measured resistance in the solenoid but it seems to be pointing at that, what else could it be?

 bob

alec(at)alecmyers.com
Guest

Posted: Mon Dec 01, 2025 3:51 pm Post subject: resistance in solenoid

 	  Quote: 	
		  measured voltage is 13.2 at battery side of solenoid and 12.6 on the load side, engine off.  


	


13.2V anywhere with the engine off is extremely suspicious. 12.6 sounds correct for a topped-off lead acid battery, but you’d have to be pulling some major current to drop 0.6V across a solenoid, and if you were pulling any major current from the battery it wouldn’t be anywhere near 12.6V still less 13.2V.



I’d recheck the 13.2V carefully.



On Dec 1, 2025, at 6:38 PM, bobnoffs <icubob(at)gmail.com> wrote:






voltage at eis is 12.6 with engine off. it is 14.3 with engine running. i have checked all numbers with eis voltage, handheld voltmeter and panel mounted voltmeter i just bought and they are all aligned.. measured voltage is 13.2 at battery side of solenoid and 12.6 on the load side, engine off.  alternator is charging fine and battery voltage is fine but after the solenoid it drops to 12.6. all this is with an earthx, not lead acid.

i haven't actually measured resistance in the solenoid but it seems to be pointing at that, what else could it be?

bob





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http://forums.matronics.com/viewtopic.php?p=516709#516709

alec(at)alecmyers.com
Guest

Posted: Mon Dec 01, 2025 3:52 pm Post subject: resistance in solenoid

Sorry - just realized you’re not using a lead-acid battery, so my voltage comments don’t apply.



On Dec 1, 2025, at 6:50 PM, Alec Myers <alec(at)alecmyers.com> wrote:



 	  Quote: 	
		   measured voltage is 13.2 at battery side of solenoid and 12.6 on the load side, engine off.  


	


13.2V anywhere with the engine off is extremely suspicious. 12.6 sounds correct for a topped-off lead acid battery, but you’d have to be pulling some major current to drop 0.6V across a solenoid, and if you were pulling any major current from the battery it wouldn’t be anywhere near 12.6V still less 13.2V.



I’d recheck the 13.2V carefully.



On Dec 1, 2025, at 6:38 PM, bobnoffs <icubob(at)gmail.com> wrote:






voltage at eis is 12.6 with engine off. it is 14.3 with engine running. i have checked all numbers with eis voltage, handheld voltmeter and panel mounted voltmeter i just bought and they are all aligned.. measured voltage is 13.2 at battery side of solenoid and 12.6 on the load side, engine off.  alternator is charging fine and battery voltage is fine but after the solenoid it drops to 12.6. all this is with an earthx, not lead acid.

i haven't actually measured resistance in the solenoid but it seems to be pointing at that, what else could it be?

bob





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http://forums.matronics.com/viewtopic.php?p=516709#516709

Ceengland

Joined: 11 Oct 2020
Posts: 395
Location: MS

Posted: Mon Dec 01, 2025 4:25 pm Post subject: Re: resistance in solenoid

Bob, your system architecture and actual measurement points need to be specified. If you're measuring Battery voltage on the source side of the master contactor, observing system voltage on your EIS, and there's any sort of isolation diode in the system somewhere, that would easily account for for the voltage difference. To get an honest number, you need to measure on each side of the contactor itself. Or, just measure across the two terminals & look for zero volts.



Charlie

_________________
Charlie

user9253

Joined: 28 Mar 2008
Posts: 1947
Location: Riley TWP Michigan

Posted: Mon Dec 01, 2025 4:36 pm Post subject: Re: resistance in solenoid

Bob,

Measure the voltage again.  But this time do NOT connect the black lead of the

 handheld meter to ground.  Instead, connect the meter black lead to the 

contactor stud on the load side.  And connect the red lead to the contactor stud 

on the battery side.  Connect meter leads directly to the contactor studs, not to 

the nuts or wire terminals.  Turn on every electrical load possible and add extra 

loads that make heat like a seat heater or automotive headlight.

_________________
Joe Gores

jluckey(at)pacbell.net
Guest

Posted: Mon Dec 01, 2025 4:38 pm Post subject: resistance in solenoid

What we know:

1. remote diagnosis is difficult at best 

2. not having a schematic makes that worse

3. the resting voltage of an EarthX is about 13.2 V





Questions:

1. have you put the voltmeter across the input and output studs of the solenoid?  With what you are describing, engine off, that reading should be 0.6 volts (13.2 in - 12.6 out = 0.6 volts)

2. does cranking current flow thru this solenoid?

3. has cranking seemed "soft" lately?

3. is there an errant diode somewhere in the circuit - just a WAG, but 0.6 v is about the drop of a silicon diode - again, just making this up 





Things you could try:

Starting with simple, no-disassembly-required tests

1. put the voltmeter across the input and output studs with everything off - what's that voltage?

2. turn on the master (but don't run the engine) - based on your description, should read 0.6v

3. start turning on high-current stuff like pitot heat, landing lights, etc - IF there is some weird resistance thru the main contacts, the voltage drop should increase as you add load.  If you have an ammeter, write down amps, what equipment is turned on, and voltage drop across solenoid.

You could have a high-resistance thru the contactor, but if starting is good, it kinda rules that out.

Also, the resistance we are talking about would be well below 1 ohm and typical multi-meters cannot accurately measure resistances that low.  Just as JoeG mentioned, you will have to use another technique to test that hypothesis.  #3 in Things to Try might shed some light on this.

Happy (gremlin) Hunting,

-Jeff

                  

                                                                        On Monday, December 1, 2025 at 03:50:03 PM PST, bobnoffs <icubob(at)gmail.com> wrote:                     

                     



                     



                                                   --> AeroElectric-List message posted by: "bobnoffs" <icubob(at)gmail.com (icubob(at)gmail.com)>



voltage at eis is 12.6 with engine off. it is 14.3 with engine running. i have checked all numbers with eis voltage, handheld voltmeter and panel mounted voltmeter i just bought and they are all aligned.. measured voltage is 13.2 at battery side of solenoid and 12.6 on the load side, engine off.  alternator is charging fine and battery voltage is fine but after the solenoid it drops to 12.6. all this is with an earthx, not lead acid.



 i haven't actually measured resistance in the solenoid but it seems to be pointing at that, what else could it be?



 bob



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bobnoffs

Joined: 04 Jul 2012
Posts: 136
Location: northern wi.

Posted: Tue Dec 02, 2025 2:56 am Post subject: Re: resistance in solenoid

i am having a hard time sorting all the replies out, going in a lot of directions. with what i have said couldnt i just jump across the solenoid while it [ the solenoid]  is turned off and check the eis voltage? if it is back to 13.2 volts i would know the problem is corroded contacts?

 bob

user9253

Joined: 28 Mar 2008
Posts: 1947
Location: Riley TWP Michigan

Posted: Tue Dec 02, 2025 5:37 am Post subject: Re: resistance in solenoid

Bob,

Yes, you can jumper across the master contactor for testing purposes.

I suspect there is an indication problem, not a problem with the contactor.

_________________
Joe Gores

bobnoffs

Joined: 04 Jul 2012
Posts: 136
Location: northern wi.

Posted: Tue Dec 02, 2025 7:52 am Post subject: Re: resistance in solenoid

thanks joe. i will try that as soon as temp gets above 15f.



 i have already checked voltage at the ''cig lighter'' with my new uninstalled panel voltmeter and my handheld voltmeter and they both read 12.6 like the eis while both reading 13.2 at the battery.

  and there is only a foot of fat wire from the battery to the solenoid where the voltage changes from 13.2 to 12.6

 bob

alec(at)alecmyers.com
Guest

Posted: Tue Dec 02, 2025 8:13 am Post subject: resistance in solenoid

Does the (13.2 minus 12.6 = ) 0.6V voltage drop appear when you measure directly across the solenoid?



Does it vary with load current - when you power the landing light, or radios?



On Dec 2, 2025, at 10:52 AM, bobnoffs <icubob(at)gmail.com> wrote:






thanks joe. i will try that as soon as temp gets above 15f.



i have already checked voltage at the 'cig lighter' with my new uninstalled panel voltmeter and my handheld voltmeter and they both read 12.6 like the eis while both reading 13.2 at the battery.

and there is only a foot of fat wire from the battery to the solenoid where the voltage changes from 13.2 to 12.6

bob





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