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Author Topic: APS/Ω Gas turbine bike build  (Read 393693 times)
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Mobacken Racing
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« Reply #1725 on: October 24, 2017, 04:44:48 PM »

Still waiting for the new LiFe battery to arrive so meanwhile I am catching up on other hobby related stuff. Nevertheless I got around to fit the new scavenge pump to the test rig tonight and it has no problem at all keeping up with the oil flow at its rated 6x flow capacity.



One thing I noticed was a slight smell of hot wires from the bike after the pumps had been running for a minute, I´ve been using very moderate cable areas so I decided then to rewire all of the big consumers before I run the engine again. Probably some half arsed wiring just for the test rig running but if it does the trick I´ll rewire the bike cable harness later.

Cheers!
/Anders
« Last Edit: October 24, 2017, 04:46:46 PM by Mobacken Racing » Logged
Mobacken Racing
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« Reply #1726 on: November 10, 2017, 04:01:07 PM »

When I wired the bike up originally I used a relay for each pump and had them switch activated, this made sense at the time but the downside is that there was a risk that I forgot to start the oil pumps before spinning the engine up on the starter. Not the end of the world since the fuel pump wouldn´t start without oil pressure but still.

There was also the fact that I was riding around with a rat nest of wires and relays cable tied between the seat and the battery, an electrical failure waiting to happen if you ask me.

Soooo, I figured that if I could get rid of all of the relays in the battery compartment I would tidy up the harness quite a bit. During the last couple of evenings I have been working at it and for the first time in my life I have actually enjoyed wiring up electrical stuff. Must have struck some feng shui nerve. Smiley



I got a delivery notice today from the company I ordered the battery, it should arrive a week from now!

Cheers!
/Anders
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« Reply #1727 on: November 11, 2017, 12:42:21 AM »

A smart and tidy electrical system is a joy to both make and look at for a true electrician! smiley
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« Reply #1728 on: November 11, 2017, 01:11:21 AM »

A sensitive infrared wave detector can spot an overheated electrical part or wire.
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Mobacken Racing
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« Reply #1729 on: November 11, 2017, 02:48:00 AM »

A sensitive infrared wave detector can spot an overheated electrical part or wire.

That is a very good idea, we have a top quality IR camera at work so I´ll borrow it some day and check the wiring out.
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« Reply #1730 on: November 11, 2017, 09:30:42 AM »

A sensitive infrared wave detector can spot an overheated electrical part or wire.
Much better method than following the smoke!  grin cheers
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« Reply #1731 on: November 11, 2017, 06:39:42 PM »

Indeed, with IR you can see where the smoke is gathering up in the wires before it pushes through.
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« Reply #1732 on: November 12, 2017, 06:58:13 AM »

Quote
Much better method than following the smoke!

An even better method is to calculate the wire size needed...

With plenty of safety factor, as a rule, and 24h/7d application, ie continuously for DC applications, 50 degree cable temp:
0.75mm2 = 6 amps,
1.5mm2 = 10 amps,
2.5mm2 = 16 amps,
4mm2 = 25 amps

You can downsize if you know for sure duty time (heating) vs rest time (cooling).
But you will need to increase if wires are near other heating devices. Most cables are rated for 70 degrees C continuous operation, some others at 90 degrees C.

Never use a fuse or breaker accordingly to the load, but always use a fuse or a breaker accordingly to the wire size...

Heat and smoke always is the result of too small a wire for the protection used... The load just takes what it needs.

DC is a strange animal that prevents the wires from cooling and reversing as on AC circuits, so always make sure your connections are clean and tightened as required. Not tight enough is no good for sure, but too tight is no good either... Proper crimp with ratchet tool and solder as well is top for DC...

Patrick
« Last Edit: November 12, 2017, 07:16:33 AM by thefrenchowl » Logged

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« Reply #1733 on: November 12, 2017, 10:38:40 AM »

Patrick;

What applies for DC also applies for AC. There is no measurable "cooling" of wires on AC. As the current varies through its cycle, the wire thermal inertia is so long compared to the AC cycle thermal heating time ( 1/2 of the 1/60 cycle in the US ) that it does not cool.

I agree with your other recommendations.

Regards, Neil  Tucson, AZ

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« Reply #1734 on: November 12, 2017, 11:58:32 AM »

Manta,

I was just refering to the fact that DC will cook copper wires and turn them into friable black dust much faster than AC for the same voltage/current if the wire and connections are not top notch. Each connection offers a tiny resistance and that's where the heat and degradation will start at 1st before going inside the wire to destroy it.

I'm not an engineer, but this might be due to the fact that in DC, all the outside layer electrons of all the atoms throughout the diameter will be replaced over time by others from the next wire or contact, while in AC, the current travel more on the outer layer of the wire and due to the alternance, most electrons will always live next to the same atom and go backwards and forwards at a much lower speed than the transmition speed which is equal to the speed of light.

If you rely a lot on electrics to make a race car, it is worth having a mate who understand electrics, to help with running as short lenghts as possible of the right size, avoid waves/returns/loops and allow for air convection cooling by not bunching cables too much.

Simplicity is also a "must achieve" goal, switches are better than contactors which are in turn better than relays... Etc down the line!

Patrick
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« Reply #1735 on: November 12, 2017, 01:17:32 PM »

Sorry, Patrick- AC and DC current will heat a wire equally if the currents are equal. The little thing that needs to be considered about AC current is that you must use the RMS value of the current. RMS is an abbreviation for "Root Mean Squared", this is the equivalent current to a DC average value.

To compute the power heating up a wire or connection: Power (watts)= I squared (amps) x R (ohms). Assume a total resistance of 1 ohm with 10 amps of DC flowing: P=Isq x R, so P=100 x 1. Power = 100 watts. Hot!
Now use an AC current of 10 amps RMS. The same equations apply, so the result is the same: 100 watts. Just as hot!

As you have alluded to the "skin effect" (where the current is carried mostly on the outside surface of a wire), this is a consideration only at UHF and microwave frequencies. At power line frequencies of 50 & 60 Hz, skin effect is not a factor. High priced stereo speaker cables are marketed as having a lower skin effect and lower distortion but that is a complete scam. Cheap 16 gauge zip cord is just as good.

Regards, Neil  Tucson, AZ

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« Reply #1736 on: November 12, 2017, 01:51:12 PM »

Neil speaks sooth, Patrick.
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« Reply #1737 on: November 12, 2017, 02:08:10 PM »

In ampacity calculations you also have to factor wire length, in dc you have take into account the length of the negative wire length if you have a complete return run of negative or ground wire. (For instance, composite bodies and chassis parts, wiring inside of campers or race car trailers and the like)

Example, ac power, 15 amp load at 20 ft, you can run a 20a breaker and 12ga romex.

If the load was dc, and power and ground start in the same area (battery)
Your wire length is now 40ft, 15a load may have bump to 6 or even 4ga wire size, depending on temperature factors as well.
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« Reply #1738 on: November 12, 2017, 10:29:54 PM »

In ampacity calculations you also have to factor wire length, in dc you have take into account the length of the negative wire length if you have a complete return run of negative or ground wire. (For instance, composite bodies and chassis parts, wiring inside of campers or race car trailers and the like)

Example, ac power, 15 amp load at 20 ft, you can run a 20a breaker and 12ga romex.

If the load was dc, and power and ground start in the same area (battery)
Your wire length is now 40ft, 15a load may have bump to 6 or even 4ga wire size, depending on temperature factors as well.


In your AC example the 20ft wire length will also double to 40ft for the voltage drop calculation.

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thefrenchowl
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« Reply #1739 on: November 13, 2017, 12:11:45 PM »

I agree with most of what you say, but is it just me who's found, time after time, age blackened/corroded brittle copper wires in car or bike DC wiring, while next to never in houses AC wiring?Huh

Or is it due to OEM cheapness!!!! My Buell Ulysses is a pig for that... Tired wiring and even more tired connectors!!!

And I can remember my 5 years in the early 70s in the French Air Force as a VHF/UHF/BLU repairer, amplifiers without any easily recognizable components in it springs to mind, but skin effect must be noticeable even at 50 or 60 Hz, my amps loading tables show you can pass more DC amps than AC amps via the same cross section wire.

; O ) Patrick
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