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Old Sep 19, 2009, 12:31 PM
It only takes one good idea
dag214's Avatar
Fishers, Indiana
Joined Oct 2004
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Help with 257" B-36D power system.

Hello all,
I have a 257" B-36 project

It will have:
6 Hacker A60-16L
6 Masterspin 77-ESC
6 ThunderPower 5000mHa, or 3900mHa batteries.

I need about 75" between the battery and the motor.

I know I can go about 36" between the ESC and motor (done this in testing with zero problems).

But I now want to look at adding Capacitors. Over on Flying Giants a guy states he has a blimp that he has 20 foot leads on using a Castle ESC. He states he is only using larger battery cables. These leads are between the battery and ESC. I have been told I cannot go longer between the battery and ESC without adding capacitors. How is he doing this???? He state by going with larger wire size it is fine to add length between the battery and ESC, I have been told this won't work.

What are my options in getting 75" or more between my battery and ESC?

I already have a thread at giant elecs, but thought this might be a thread that could help:
http://www.rcgroups.com/forums/showthread.php?t=933242

Thanks a ton, DAG
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Old Sep 19, 2009, 03:38 PM
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mattyhawk's Avatar
Oxnard, Ca
Joined Oct 2008
1,796 Posts
Hey Dag, I've been following your build for a while, looks so cool.

There is a thread on this, check it out:

http://www.rcgroups.com/forums/showthread.php?t=952523
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Old Sep 19, 2009, 03:52 PM
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mattyhawk's Avatar
Oxnard, Ca
Joined Oct 2008
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Can you just have a hatch for each nacelle or each wing and mount the battery so they maintain short runs? 36" is quite long.
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Old Sep 19, 2009, 04:33 PM
It only takes one good idea
dag214's Avatar
Fishers, Indiana
Joined Oct 2004
5,805 Posts
Quote:
Originally Posted by mattyhawk
Can you just have a hatch for each nacelle or each wing and mount the battery so they maintain short runs? 36" is quite long.
I have a CG problem with the battery placement, not where the ESC or batteries can fit.

Thanks, DAG
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Old Sep 20, 2009, 07:19 AM
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Joined Dec 2008
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Hey DAG,
Been following you thread in Giant Scale since the beginning.

I find it really a big surprise that all these electrics types argue about how to do these powersystems and the know it all's won't even help you here.

I have a buddy that added pan-caps the "M" series and his ESC works great. He added 1 per every 3-4".

I am not a expert, but at least I tried to help. And that guy over at FG that states he is using 20' lengths of wire to his ESC is just asking for problems.

Good Luck, Nick
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Old Sep 20, 2009, 07:20 AM
It only takes one good idea
dag214's Avatar
Fishers, Indiana
Joined Oct 2004
5,805 Posts
Well all,
After reading everything posted here I see I am going to add caps. In more testing I see with the 10 gauge wire that I can have a safe lead length of 30" (ESC to Motor) and not get close to my 100c cut off. By having that headroom I can place the ESC at the leading edge air scoop on each engine nacelle. Then by adding caps I can get my batteries where I want in the wing/fuse to get my CG correct.

Thanks mattyhawk,

DAG
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Old Sep 20, 2009, 07:22 AM
It only takes one good idea
dag214's Avatar
Fishers, Indiana
Joined Oct 2004
5,805 Posts
Quote:
Originally Posted by f104nick
Hey DAG,
Been following you thread in Giant Scale since the beginning.

I find it really a big surprise that all these electrics types argue about how to do these powersystems and the know it all's won't even help you here.

I have a buddy that added pan-caps the "M" series and his ESC works great. He added 1 per every 3-4".

I am not a expert, but at least I tried to help. And that guy over at FG that states he is using 20' lengths of wire to his ESC is just asking for problems.

Good Luck, Nick
Thanks Nick also,
I think I am on the right direction, I am going to be using these caps : http://search.digikey.com/scripts/Dk...&name=P5314-ND

I think they are the right ones.

Thanks a ton,
DAG
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Old Sep 20, 2009, 08:45 AM
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vintage1's Avatar
East Anglia, UK
Joined Sep 2002
29,687 Posts
I would not be too happy with such small capacitors on such long wires.

The actual analysis of what you DO need is fiendish as well. To the point where I would be tempted to say, 'try it' and see if it blows up, or not enough power seems to be getting through.


I can maybe outline the issues, and its up to you how you approach them.

1/. Straight voltage drop down the battery leads. Don't underestimate this: Just because the cable ain't smokin' hot, doesn't mean you are not getting a drop. Consider using wire that is the sort of grade used for small car or bike starter motors. Like about 1/4" diameter. This is heavy. One tick for 'put batteries in nacelles'. Now that current gets pulled in pulses. Its very messy, and you want to make sure its as even as possible, which means something BIG and FAT in the way of a capacitor. Especially at part throttle.

Which leads to maybe over 1000 uF At whatever is a suitable voltage. I'd guess 50v typically.

2/. Instability due to lead inductance. This is the killer, and what the smaller caps normally in place are for. If the ESC does go unstable, it will smoke in seconds . Again BIG FAT leads have less inductance and less resistance, and help a little. But what you need here is a LOW ESR capacitor in the sort of 100uF area, that has less series inductance and resistance than the BIG FAT capacitor you already put in.. IN addition, you might consider the biggest fattest NON electrolytic capacitor you can find. - maybe a 1 uF or so, of the interleaved flat plate sort..mylar or polycarbonate maybe, that will act as a good RF bypass.


Now that's the belt, braces, safety pin and a bit of string approach. I cant say from here which are needed and which might not be.

However I can suggest a way you might find out.

Firstly, set up a test rig for a single engine and pack, and using a whattmeter and preferably a tacho, establish a baseline. measure RPM and power at a given throttle setting with a medium prop load..don't go as far as full prop, as static running isn't as kind as in the air - and at full power and note them down.

Next, use a long bit of cable, and ALL those components at the far end, to be safe. Check the readings again. If you are losing significant power, you need fatter wire.

So play that way till the power at least is adequate., You will always lose some, but its your call when its too much.

Now, with the rig running, cut the wire to the small cap (1uf or so) you added. If there is no perceptible change in RPM or current, and the thing throttles up and down smoothly, .then there was enough of that already on board the ESC.

Now very carefully snip the BIG FAT capacitor, and check again. If the ESC doesn't smoke, at least its STABLE with just the small extra one, but you will, especially at part throttle, see an efficiency loss. Again it's your call as to whether the efficiency loss is worth the weight gain.

Finally, with whatever capacitors you end up with, do a full flightplan on the bench, to check they are not overheating. If they do, you need more, or lower ESR ones (effective series resistance).

Or you may decide that a pack per motor in the nacelles is actually a damn sight less hassle. That works for me too. Do consider effects of one or more moors shutting down early, too.
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Old Sep 20, 2009, 09:00 AM
I need more room!
mrblucor's Avatar
Cape Cod MA
Joined Nov 2005
334 Posts
Dag214,
Along with caps along the long run of wire, I would also twist the battery leads together. This will reduce the loop area ie. reduce potential interferance.

With large ESC's and added capacitance, I would also make a seperate parallel positive lead with a 10 - 20 Ohm resister in series. Connect the resister lead first, this will eliminate the large spark you would get without it. This will save your battery connecters from damage. Then connect your main power lead.

JB
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Old Sep 20, 2009, 09:03 AM
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East Anglia, UK
Joined Sep 2002
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Good points, that I forgot to add. Thank you.
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Old Sep 20, 2009, 10:03 AM
It only takes one good idea
dag214's Avatar
Fishers, Indiana
Joined Oct 2004
5,805 Posts
Quote:
Originally Posted by vintage1
I would not be too happy with such small capacitors on such long wires.

The actual analysis of what you DO need is fiendish as well. To the point where I would be tempted to say, 'try it' and see if it blows up, or not enough power seems to be getting through.


I can maybe outline the issues, and its up to you how you approach them.

1/. Straight voltage drop down the battery leads. Don't underestimate this: Just because the cable ain't smokin' hot, doesn't mean you are not getting a drop. Consider using wire that is the sort of grade used for small car or bike starter motors. Like about 1/4" diameter. This is heavy. One tick for 'put batteries in nacelles'. Now that current gets pulled in pulses. Its very messy, and you want to make sure its as even as possible, which means something BIG and FAT in the way of a capacitor. Especially at part throttle.

Which leads to maybe over 1000 uF At whatever is a suitable voltage. I'd guess 50v typically.

2/. Instability due to lead inductance. This is the killer, and what the smaller caps normally in place are for. If the ESC does go unstable, it will smoke in seconds . Again BIG FAT leads have less inductance and less resistance, and help a little. But what you need here is a LOW ESR capacitor in the sort of 100uF area, that has less series inductance and resistance than the BIG FAT capacitor you already put in.. IN addition, you might consider the biggest fattest NON electrolytic capacitor you can find. - maybe a 1 uF or so, of the interleaved flat plate sort..mylar or polycarbonate maybe, that will act as a good RF bypass.


Now that's the belt, braces, safety pin and a bit of string approach. I cant say from here which are needed and which might not be.

However I can suggest a way you might find out.

Firstly, set up a test rig for a single engine and pack, and using a whattmeter and preferably a tacho, establish a baseline. measure RPM and power at a given throttle setting with a medium prop load..don't go as far as full prop, as static running isn't as kind as in the air - and at full power and note them down.

Next, use a long bit of cable, and ALL those components at the far end, to be safe. Check the readings again. If you are losing significant power, you need fatter wire.

So play that way till the power at least is adequate., You will always lose some, but its your call when its too much.

Now, with the rig running, cut the wire to the small cap (1uf or so) you added. If there is no perceptible change in RPM or current, and the thing throttles up and down smoothly, .then there was enough of that already on board the ESC.

Now very carefully snip the BIG FAT capacitor, and check again. If the ESC doesn't smoke, at least its STABLE with just the small extra one, but you will, especially at part throttle, see an efficiency loss. Again it's your call as to whether the efficiency loss is worth the weight gain.

Finally, with whatever capacitors you end up with, do a full flightplan on the bench, to check they are not overheating. If they do, you need more, or lower ESR ones (effective series resistance).

Or you may decide that a pack per motor in the nacelles is actually a damn sight less hassle. That works for me too. Do consider effects of one or more moors shutting down early, too.
Thanks a ton for responding. I really do appreciate it.
Can you suggest a part number for the caps you would suggest for testing???

Thanks a ton,
Cheers, Damon
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Old Sep 20, 2009, 10:06 AM
It only takes one good idea
dag214's Avatar
Fishers, Indiana
Joined Oct 2004
5,805 Posts
Quote:
Originally Posted by mrblucor
Dag214,
Along with caps along the long run of wire, I would also twist the battery leads together. This will reduce the loop area ie. reduce potential interferance.

With large ESC's and added capacitance, I would also make a seperate parallel positive lead with a 10 - 20 Ohm resister in series. Connect the resister lead first, this will eliminate the large spark you would get without it. This will save your battery connecters from damage. Then connect your main power lead.

JB
Thanks, where does the resistor go? Between +/-? On the battery or the ESC leads?

Thanks a ton.

DAG
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Old Sep 20, 2009, 10:12 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
near Nijmegen, Netherlands
Joined Feb 2001
10,451 Posts
Preventing battery sparking:
http://www.rcgroups.com/forums/showthread.php?t=876173

Vriendelijke groeten Ron
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Old Sep 20, 2009, 10:29 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
near Nijmegen, Netherlands
Joined Feb 2001
10,451 Posts
Most of you have probably seen this post before ...

I compiled expert (EE's) statements and ESC manufacturer (all!) statements, they all say the same, extend brushless motor wires, not battery wires. Long battery wires will kill your ESC over time. If you must extend battery wires you have to add extra caps. Said statements, rules of thumb, installation manuals and pictures, a watery explanation and theory:
http://www.rcgroups.com/forums/showthread.php?t=952523

Vriendelijke groeten Ron
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Old Sep 20, 2009, 12:50 PM
It only takes one good idea
dag214's Avatar
Fishers, Indiana
Joined Oct 2004
5,805 Posts
Quote:
Originally Posted by Ron van Sommeren
Preventing battery sparking:
http://www.rcgroups.com/forums/showthread.php?t=876173

Vriendelijke groeten Ron
Very cool, all your are doing is dissipating the charge before you hook up the hot, right?

Thanks, DAG
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