Ground Power Receptacle / External Power Plug / Starter motors ?

vic wrote:

And when talking of real reduction gear of say, 4:1 and same crankshaft speed as before, you will need a motor one quarter of the power but four times the motor shaft speed for same crank speed. So you will obviously have only one quarter of amps as the torque will be upped by the gearing – right ?

That’s nonsense, as I already wrote. If you increase speed, current draw will go up as well. You can lookup the equations. It can’t be any other way, it would be an obvious hole in laws of physics.

tomjnx wrote:

Doesn’t make sense to me.

I agree. It can be difficult with low powered computers to find a PS that’s of high quality and has the bells and whistles you want (modular cabling, etc.) with low enough rating so it’s nicely loaded while in operation (it’s been years since I built any computer, might have changed). Unless that computer can do at least 250 W at full tilt, Peter’s choice doesn’t make sense to me.

There is another angle here: fanless power supplies have a poor reliability record. They develop hot spots, because they don’t have a fan.

We have some fanless servers and they have the power supply as an external “power brick”; about 100W rating.

But also one pays extra for quality – as always – and the more pricey power supplies are rated at higher powers, presumably for perceived value improvement

And finally, I used to build power supplies for a living, and thermal cycling is the biggest killer in electronics, by far. This is a particular challenge in fanless computing. With motherboards it’s not too bad because you have to attach heatpipes (or a huge heatsink, and have lots of ventilation) to only 2 or 3 places, but power supplies have a larger number of bits which can get hot.

Allright, I surrender. Seemingly the term reduction gear is not universally accepted as a gearbox that reduces rpm from motor shaft input to some LOWER rpm on the output shaft. That is solely what I am talking about: Take a smaller motor that does a lot higher rpm and mate that to a reduction gear that lowers this high speed to useful crank speed and you will definitely see lower amps drawn. That is the idea of a reduction gear, not turning the crank faster than before. Although you can do that as well with a reduction gear, just let the electric motor spin even faster to have the cranking speed higher. Vic

I was hoping to get a video today of an “old” starter (somebody spent ages starting some plane) and my Skytec one, but the phone kept falling off the top of the panel

I think the way it works is that the torque required to spin the engine is probably constant regardless of how fast you spin it (because, basically, you are driving the cylinder compression) so if you want to spin it 3x faster you need 3x more power. So at the given supply voltage you will need 3x the current. How the starter is itself constructed (geared or direct drive, how many poles on the motor, etc) is to a first degree approximation irrelevant.

Are there really any direct drive starters? You would need a lot of poles on the motor to get the required low RPM, and/or the commutator would be passing a lot of current, the windings would have to be very thick, and the rotor/stator airgap would be critical because the flux density would be that much greater. Both the traditional Lyco starter and the Skytec ones are geared.

About all car and truck starters are direct drive, no reduction gears in the starter itself. Geared starters are relatively new to ground transport but picking up for obvious reasons – to get drawn amps down. All this is meant for keeping the SAME cranking speed as before. Spinning the crank FASTER than originally is a different matter. But then you don´t need a REDUCTION gear, instead a stronger motor which is able to turn faster at the same torque the crank needs. Yes, car starters have VERY thick wires to stand hundreds of amps. Vic

vic wrote:

Seemingly the term reduction gear is not universally accepted as a gearbox that reduces rpm from motor shaft input to some LOWER rpm on the output shaft.

I understand exactly what you mean. I’m assuming the rotational speed of crankshaft stays the same, just as the engine stays the same (the torque required). You’re saying that reduction of torque means reduction of current flow. But reduction of speed of the electric motor means reduction of current flow as well. If you employ gearing to reduce torque at an output shaft of an electric motor, you have to increase speed to get the same torque and speed at a crankshaft. Current flow stays the same. What you save by decreasing torque, you spend by increasing speed. Assuming everything else stays the same. How many times do I have to write it? Power just doesn’t come out of nowhere. To increase speed (which means increase in output power) you have to increase input power (which means more current if the voltage stays the same).

Of course, the electric motor speed has to be a lot higher when a reduction gear is fitted to it to maintain the same crank speed – I said that a few times. Maybe you get the picture: The normal starter and flywheel combination is a reduction drive basically, as the starter has maybe 10 teeth and the flywheel maybe 100, so reduction of 10:1. You see maybe 200 amps drawn when starting. Now imagine no reduction here but instead you mount a BIG electric motor direct to your crank at 1:1 . What do you think the motor would look like and how many amps would you see ? So then, what does a reduction gear do to current flow ? Vic

Peter wrote:

There is another angle here: fanless power supplies have a poor reliability record. They develop hot spots, because they don’t have a fan.

This falls under quality for me. And as I wrote, its not easy to get high quality with low rating, at least that was my experience. But you want the low rating.

vic wrote:

Geared starters are relatively new to ground transport but picking up for obvious reasons – to get drawn amps down

And here I thought the first geared starter in an automotive application was in like ‘60s. And that they are in majority, not something new. Don’t know whether the integrated starter-generators that are used a lot these days are geared or not, but I would think it’s a good bet.

I found a few pictures at Ebay to show both types of starters, direct drive and geared. The direct type is very slim, only the relay/coil mounted on top of the motor. Vic

geared starter

direct drive

Martin wrote:

And here I thought the first geared starter in an automotive application was in like ‘60s. And that they are in majority, not something new.

Geared permanent magnet automotive starters started to become prevalent about 25 years ago. The early ones (Valeo for example) had various problems with glued magnet retention when run hot, and with the grease lubricated reduction gears.