Connecting Ground Power will not turn over engine with drained battery

Quoting old thread:

I would need to check or get a spitfire expert to comment, but my understanding was the ground power was just for the starter and radios and so on, it did not charge the onboard battery.

Ground Power is for starter, what I always assumed, makes perfect sense. But ...

I've noticed many times, engine refuse to turn over, battery seems low, after repairs. Connecting Ground Power doesn't help. So I did a simple experiment with P-51 and with Spitfire (Summer +20'C).

1) Spawn "Takeoff from runway" (This assured engine temp/oil pressure was up, no damaging engine by turning over cold)

2) Shut off magnetos (engine stops)

3) Spun the starter until battery drained (prop stopped moving)

4) Attached Ground Power and attempted to start.

P-51 started (as it should). Spitfire prop didn't turn over at all (voltmeter showed 5V (down from initial 14/15V), whatever that means *1)

If Ground Power is for starting, which again makes perfect sense, then this is a simple well defined bug. Ground Power should power the starter in an undamaged aeroplane.

*1) Would ground power really bypass the voltmeter? If it does, be that as it may, the important point here is that ground power doesn't power the starter.

I made a video production to get more attention, sue me.

This bug seems simple and well defined. Spitfire doesn't get any "Ground Power".

Who cares, how often does one drain battery anyway? Often enough after repair (20%?) to be annoying when it can't start again. This *is* a bug, unless someone explains why it isn't.

Note (as final screen also says), I don't think Spitfire gets any ground power, not to starter, not to dash lamps, not anywhere.

Have tracks.

I just had this experience with the P-51. Kept landing (and crashing/repairing a lot) on Carrier. It refused to start. Connected Ground Power and happiness ensued;) (it started).

Wish the Spitfire worked with Ground Power.

Can someone confirm this?

It's very easy. Takes 30 min to drain battery. Make a starter HOTAS binding so you don't have to hold the key down.

Then connect ground Power and note that Spitfire does not get any power anywhere, not starter, not instrument lights.

Nah, max time acceleration and left click is enough :D.

Can confirm, although I'm more puzzled by the fact that starter can go for so long. I seem to recall back in 1.2.xx times starter in the Mustang was overheating and faililng if used too long.

Thanks. Ground Power not providing *any power* anywhere *is* a bug. Fishing for BIGNEWY to say REPORTED.

Ground Power not providing *any power* anywhere *is* a bug.

Would like to see the schematics before saying anything definite. It's possible that on some systems, there's a relay closing the GP circuit when it is powered by the battery after the latter has been switched on; however, whether such schemes were actually in use is debatable.

But the starter turning for 30 minutes without burning out? Now THAT's a bug for sure :D

Would like to see the schematics before saying anything definite. It's possible that on some systems, there's a relay closing the GP circuit when it is powered by the battery after the latter has been switched on; however, whether such schemes were actually in use is debatable.

 

But the starter turning for 30 minutes without burning out? Now THAT's a bug for sure :D

It is not spitfire uses 12 V but starter is 24 V so starter works at much lower power level then was designed.

much lower power level

Still not sure about that. How much current does it draw? How thick is the wiring? How hot does it get over time? What's the circuit resistance? Would really like to see some data, or at the very least, anecdotes supporting the claim of it being able to run for half an hour loaded.

Because it's not just the voltage in isolation. That only gives you a higher possible average power level if your circuit can handle the current for longer periods of time. Peaks are a different animal altogether.

But I'm not claiming anything. It's also entirely possible that the starter system can do this. I'd just like to see some data.

so starter works at much lower power level then was designed

All else being equal, it definitely does not. Quite the contrary. What happens if you replace a 6V power source with a 12V one and leave the circuit it feeds unchanged?

All else being equal, it definitely does not. Quite the contrary. What happens if you replace a 6V power source with a 12V one and leave the circuit it feeds unchanged?

Exactly when 24 V starter is hooked up in to 12 V installation it will barely move :)

When 12 V starter is hooked up in to 24 V installation it will melt commutator or circuit breaker will pop up o

Ah, misunderstood you. So they're using a 24V starter with a 12V system? That explains it...

Would like to see the schematics before saying anything definite. It's possible that on some systems, there's a relay closing the GP circuit when it is powered by the battery after the latter has been switched on;

?

I can imagine clever circuitry for many reasons but Ground Power is for engine start and this doesn't work, so therefore I call it a bug.

It doesn't seem to do anything. It doesn't provide power to the starter (that's the point of ground power). It doesn't provide power to the instrument lamps. Running for 30 mins is a lesser bug.

?

I can imagine clever circuitry for many reasons but Ground Power is for engine start and this doesn't work, so therefore I call it a bug.

 

It doesn't seem to do anything. It doesn't provide power to the starter (that's the point of ground power). It doesn't provide power to the instrument lamps. Running for 30 mins is a lesser bug.

Agree, ground power in most cases are used for starting engine. I will point couple things

1st. Cranking speed of the starter should be significantly higher then in case of running internal battery only.

2nd. In cold temps ww 2 battery is almost dead, probably making it impossible to start engine on internal battery only.

Ground power is simply cart with big ass battery.

Ground Power is for engine start

Not only. Someone correct me if I'm wrong, but to my knowledge most GP feeds power up other vital A/C systems too, and depending on the plane, there may well be something installed that needs several supply voltages switched on in a particular order.

Now suppose you have a device that needs both 12V DC from the battery and, say, 48V AC from the GP supply, and the battery voltage must be switched on first. How do you ensure this'll indeed happen? Easy. You hook up a relay that only closes the GP circuit after the battery switch has been turned on - and how do you know our Spit doesn't have any such devices installed, since no-one has produced any schematics yet?

Mind you, I'm not claiming that this can't be, or won't be, a bug. The above is all hypothethical. I'm just saying we don't know yet.

cart with big ass battery

A generator too if you need AC.

Spitfire uses only 12V DC. So in case Warbirds it will be only cart with big ass battery :)

In case other planes it maybe AC/DC or even air supplied by ground power unit.

Any way in cold temps engine require more force for cranking and battery in low temps provide less peak amperage, this should impact cranking speed and hooking up ground power should improve this a lot.

P-51's manual says that ground power should be used for starting when ever it is possible.

I'd like to see some info on the starter too

I find it difficult to believe that the starter was either higher or lower rated than the actual voltage available.

I only know automotive DC starters but in my experience what would happen is exactly what grafspee stated at #11

Seen cases where coils are given over voltage to help ignition systems during starting, but I don't think that's relevant as aircraft use magnetos

Now suppose you have a device that needs both 12V DC from the battery and, say, 48V AC from the GP supply, and the battery voltage must be switched on first. How do you ensure this'll indeed happen? Easy. You hook up a relay that only closes the GP circuit after the battery switch has been turned on - and how do you know our Spit doesn't have any such devices installed, since no-one has produced any schematics yet?

 

Mind you, I'm not claiming that this can't be, or won't be, a bug. The above is all hypothethical. I'm just saying we don't know yet.

Could be, doesn't quite make sense to me though. Year ago I dug into the F-86 electrical system. External power connects to battery through a cascade of relays at the ideal charging voltage. Anyway, if Spitfire is dependent on a working charged battery then it is an another kind of bug. "Repair" doesn't guarantee a good charged battery and therefore sometimes it can't be started.

F-86 external power and battery. Note leads marked [1] non-existent on 35 (our) version.

Seen cases where coils are given over voltage to help ignition systems during starting, but I don't think that's relevant as aircraft use magnetos

In case of Merlin engine magneto powered coils will not work/ or will not provide strong enough sparks for ignition so there is battery based coil which provide spark at low rpm while engine is starting(this booster coil is working even when magneto switches are in off position, in case of spitfire there is separate button for this but in p-51 pilot when using starter always running ignition hot so very dangerous compilation),

so ground power do 2 things, helps maintaining higher voltage during start up and helps cranks engine faster. higher voltage is beneficial for battery feed coil.

F-86 has electric starter but engine require so much power to be started up that internal battery would not have a chance.

+ f-86's starter is quite different from Merlin's because of the nature of starting procedure.

through a cascade of relays

Also isolates the starter and the battery circuits from each other, probably to protect the other circuitry from voltage fluctuations and/or spikes during the startup. But this hardly explains anything about the Spit, does it ;)

This starter / battery bus isolation is actually very common in more modern A/C I've heard. Just wonder if any of the WW2 crates used it. And how, if they did.

This starter / battery bus isolation is actually very common in more modern A/C I've heard. Just wonder if any of the WW2 crates used it. And how, if they did.

You cant isolate battery from starter in spit if you want start this thing up,

In p-51 all lights go dime while cranking so probably no circuit cut off.

In cars you have the same, most of systems are cut off while starter is engaged.

if you want start this thing up

So it doesn't start when the GP is connected and the battery is off? Now wouldn't that be analoguous to having a dead battery onboard? Because none of that should matter if the RL GP and battery buses are connected in parallel.

So it doesn't start when the GP is connected and the battery is off? Now wouldn't that be analoguous to having a dead battery onboard? Because none of that should matter if the RL GP and battery buses are connected in parallel.

Yes, Unless GP connector is not provide power to all systems, what if it provide power only for starter, i don't know how electric system looks.But isolating only internal battery make no sense for me, It is more likely that vulnerable electric systems will be isolated from power while cranking but only internal battery. Some how this looks weird for me.