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Brand new PC-680 drops to 9v when cranking?

moespeeds

moespeeds

Well Known Member
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My battery is in the back of my 8, behind the baggage compartment.

IO 360 is slow to crank, and tends to stall at TDC.

Battery holds 13v, but drops to 9v when I crank, right at the terminals. No voltage drop from the battery to the starter. From what I've read, I need a minimum of 10v to properly spin this skytec lightweight starter and RV200 prop.

I did get this battery on Amazon. Before I go buy another, is there something the same size and weight that puts out more CCA? Not concerned about saving money, looking for the most output in that size and weight range.
 
moespeeds said:
My battery is in the back of my 8, behind the baggage compartment.

IO 360 is slow to crank, and tends to stall at TDC.

Battery holds 13v, but drops to 9v when I crank, right at the terminals. No voltage drop from the battery to the starter. From what I've read, I need a minimum of 10v to properly spin this skytec lightweight starter and RV200 prop.

I did get this battery on Amazon. Before I go buy another, is there something the same size and weight that puts out more CCA? Not concerned about saving money, looking for the most output in that size and weight range.
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The EarthX 680 will do it.

Their 900 will spin it a LOT faster.
 
My one behaved the same when new. There's a procedure to improve battery performance of the PC680, description also here at VAF. i did that and since then the battery performs great in combination with the skytech starter and io360. probably not necessary to throw it away.
 
Moe, you mentioned checking for voltage drop from battery to the starter, also you could check from the starter to airframe ground. It does sound like you got a weak Amazon battery.. maybe have autozone do a load check over the counter? I wonder what the “conditioning” the above guy is talking about..
If you go with EarthX, it'll crank over like there are no spark plugs in it! Rumor has it you can fly an additional 10 miles after running out of gas by cranking it!
 
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https://vansairforce.net/community/showthread.php?t=139740

Maybe your battery sulfated. All the info needed is above. I used a simplified process... just drained the battery with low load (only avionics running) down to stabilized 9 to 10 Volts and recharged it with high amps. Did that two or three times. Before that procedure it was almost impossible to spin the propeller (at summer temps), after that it cranked easely and i never had a weak battery problem over the last two years. I think it's worth a try, before spending time and money for a new battery.
 
I know several builders, same starter battery combination, same problem. Not sure if it's an awg issue (some use 2 awg, some up to 6 awg) for the wiring or ground. (Post mentioned no voltage drop but that is really not possible with the length of run) either replace the starter or get an EarthX battery (Preferably the ETX-900, same case as the ETX-680). Most find it easier to replace the battery.
 
dmattmul said:
I know several builders, same starter battery combination, same problem. Not sure if it's an awg issue (some use 2 awg, some up to 6 awg) for the wiring or ground. (Post mentioned no voltage drop but that is really not possible with the length of run) either replace the starter or get an EarthX battery (Preferably the ETX-900, same case as the ETX-680). Most find it easier to replace the battery.
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The PM starters draw approx twice the current of the wire wound units I mentioned and that's when they are new, not to mention they generally have a shorter than average life from my experience. You can try band aiding it with a bigger EX battery but that's not a great solution IMO to 'fix' a bad starter.
 
dmattmul said:
I know several builders, same starter battery combination, same problem. Not sure if it's an awg issue (some use 2 awg, some up to 6 awg) for the wiring or ground. (Post mentioned no voltage drop but that is really not possible with the length of run) either replace the starter or get an EarthX battery (Preferably the ETX-900, same case as the ETX-680). Most find it easier to replace the battery.
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The voltage drop was barely .2v, not worth mentioning as it's clearly not what's causing the starter to drag. 2 AWG wire run. Chassis ground checked out fine.
 
dmattmul said:
I know several builders, same starter battery combination, same problem. Not sure if it's an awg issue (some use 2 awg, some up to 6 awg) for the wiring or ground. (Post mentioned no voltage drop but that is really not possible with the length of run) either replace the starter or get an EarthX battery (Preferably the ETX-900, same case as the ETX-680). Most find it easier to replace the battery.
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For the record, 6 AWG is smaller than 2 AWG.
 
Yes, I know just did not sound grammatically correct to say down to 6 awg. Most knew what I meant. :D When I purchased my Lycomings I specifically asked for the NL starter to be installed. (Light weight starter has been an ongoing issue)

My day job for the last 40+ years was producing the windings (magnet wire in North America, also called winding wire in Europe and Asia) for over 50% of the motors and transformers made in North America.
 
dmattmul said:
or get an EarthX battery (Preferably the ETX-900, same case as the ETX-680). Most find it easier to replace the battery.
Click to expand...

Planning to replace my PC680 this condition inspection as its performance has noticeably degraded on starting (battery is 7 years old). Is the ETX-900 a drop-in replacement for the PC680? And yes I have the Skytech lite weight starter.
Figs
 
uk_figs said:
Planning to replace my PC680 this condition inspection as its performance has noticeably degraded on starting (battery is 7 years old). Is the ETX-900 a drop-in replacement for the PC680? And yes I have the Skytech lite weight starter.
Figs
Click to expand...

Seems that other than physical size your alternator has to be a certain size. Seems the range is stated as x or less out put . Seems too much and the battery doesn’t like, but less is better.

“ This battery is intended for 540ci engine size or less; 80 amp alternator/generator or less”
 
Cranking

Moe,

Get an NL starter and an ETX 900 battery, you will have so much power you will be able to taxi with the starter alone!

Kidding aside, just sent you a PM
 
A few notes...

The application is an -8 with a rear battery, ergo a CG shift was desired. A PC 925 is thus another option. I use one to crank a 390 and move the CG.

Like Walt, I don't think much of the PM/LS series starters. The NL has generally been good.

The available rush current from an EarthX is well accepted, so yes, it may fix the cranking problem. However, (1) it would need to be the vented box version, as it's inside the fuselage, and (2) its low mass would be the opposite of what is desired for CG in this application.

Nuckolls has stated that B&C uses 8.5V as their battery condition benchmark. Remember, digital meters may freeze the highest value or average all the values. In reality amps go up and volts go down as each cylinder approaches TDC. The least voltage value may be quite low.
 
thanks Brian & Butch, could have searched myself, just not the time, at the time :)

Been thinking about swopping my 680 for an Earth for a while, mainly for the weight advantage. On my original location RV-6.9, the battery already is in an aluminum case, inside the cockpit, between the rudder pedals.
So in theory, I would just have to add venting... not sure how, though.
One way I'm thinking off is a 90° elbow fitting off the bottom of the box, turned towards the rear, hopefully creating a suction in the battery box. This should suck out any lethal fumes should they arise...
 
Dan57 -- Understood :)

In the "for what it's worth" category - I followed Van's drawing 31A and used an Odyssey PC680 for years/100's of hours without trouble.

I recently (3 years) changed to the EarthX ETX680 & EarthX aluminum battery box to save a few lbs.

I am running a stock YIO-360-A1B6 with a PM/LS starter -- aside from early failure of the solenoid, the unit has been fine. It spins the big angle valve like a top, which fires off on the first blade.
 
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Battery mount

Dan,

My answer is yes. I have a PC680 in the aft baggage compartment in my -8 and got an empty ETX900 case from EarthX for fitment. I removed the PC680 and inserted the ETX 900 case into my battery mount and it fit. It is just a tad thicker than the 680 but it fits. With that in mind I expect the ETX680 to be a drop in replacement as well since they use the same case (6.5” x 3.1” x 6.6”). Since both batteries have the screw in terminal posts in the same location my battery cables will work nicely with no adjustments.

One thing is confusing though- if an EarthX battery would be mounted in the fuselage why is the ETX 900 recommended to install with a vented version but there is no ETX680 vented model?
 
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Vent or not

I'm guessing that Earth X wanted as few different models as possible and needed a vented version for people who mount in area's that could possibly lead to smoke inhalation. The 900 was a middle of the road model with the 680, 900 and 1200 all sharing the same case. I'm not sure of the 8 design but most 10's who use Earth X batteries in the rear are not using the Earth X vented version. Earth X as least did at one time say it was ok to use the non-vented version in the back of a 10 as the draft was more than adequate to take care of a venting need. Heat seems to be one of the biggest concerns. I'm told the Earth X chemistry is more suited to higher temps than a standard lead acid battery, but I have seen not data for this. Heat of course should not be an issue in the back of an 8 or 10.
 
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