Author Topic: Extending Battery Leads (Read 773 times)

Jim Moffatt · « **on:** January 14, 2010, 10:53:44 AM »

I want to add 1 ft. to my battery leads on a 30 amp esc. From what I have gathered, extending battery leads can cause esc problems unless you increase the input capacitor value. Are there any rules of thumb on how much to increase the capacitance? Also does anyone know the failure mechanism, is it in flight or on connect/disconnect?

(After posting this I found this excellent link.)

http://www.rcgroups.com/forums/showthread.php?t=952523&highlight=battery+lead

Crist Rigotti · « **Reply #1 on:** January 14, 2010, 11:16:31 AM »

Check out this website. They have good info on adding caps to extended battery wires.
http://www.schulze-elektronik-gmbh.de/tips_e.htm

Mike Scholtes · « **Reply #2 on:** January 14, 2010, 11:39:52 AM »

I am interested in this question too, though the practical answer appears to be that extending six inches or so makes no difference (see my post below and responses). The info on the German site appears to date from early 2003, an eternity ago in electric propulsion. Is the info still valid for the ESCs we use now, and valid for ESCs other than the "future" (whatever that is) ESC referenced in the data?

Alan Hahn · « **Reply #3 on:** January 14, 2010, 12:13:28 PM »

Mike,
Maxwell's Laws (dating from 19th century) for Electricity and Magnetism are still valid today!

Jim Moffatt · « **Reply #4 on:** January 14, 2010, 12:15:44 PM »

Thanks all, I found this excellent thread on RC Groups power systems - it tells a lot about it.

http://www.rcgroups.com/forums/showthread.php?t=952523&highlight=battery+lead

I probably killed two escs by using a series ammeter with leads 5 ft long!
(Too soon old - too late smart!)

John Cralley · « **Reply #5 on:** January 22, 2010, 08:16:39 AM »

After reading this thread and the RCgroups forum thread, I became concerned about zapping my ESCs with long leads when measuring AMPs and Watts with my setups. I surfed and found low inductance 220 uF 35 volt aluminum electrolytic capacitors from Digi-Key for .274 each. I ordered 20 and with shipping they come to about 58 cents a piece (shipping is more than the item cost LOL). (P12411-ND .27400 5.48 T: CAP 220UF 35V ELECT FM RADIAL: SCHED B: 853222)

I'm not planning on any excessively long battery leads right now but when I use my Astro Flight "Whatt" meter I am in the 18 to 24 inch lead range. From the RCgroups forum it appears that the extra capacitors are added as close to the ESC as possible. Since I am not eager to add capacitors to all of my ESCs, I am wondering if I can simply add them to the ESC plug end of of the meter cable. This would have the capacitors removed from the ESC by the length of the ESC to battery plug cable (usually about 3 or 4 inches). I'm definitely not an electrical engineer so, though this seems like this setup would also trap inductance spikes, I am asking for opinions from the folks on this forum who know. I also wonder how many of these capacitors would be a reasonable number to splice in to the cable assuming that this idea will work.

Up until now, I have had no ESC failures using the meter but I only use it a brief time to get a reading and then shut down the motor. I have, however, noted that the capacitors on the ESC do get warm (100+ degrees) when I make measurements.

I do feel that tis better safe than sorry.

Thanks, John

Alan Hahn · « **Reply #6 on:** January 22, 2010, 08:54:01 AM »

Quote from: John Cralley on January 22, 2010, 08:16:39 AM

After reading this thread and the RCgroups forum thread, I became concerned about zapping my ESCs with long leads when measuring AMPs and Watts with my setups. I surfed and found low inductance 220 uF 35 volt aluminum electrolytic capacitors from Digi-Key for .274 each. I ordered 20 and with shipping they come to about 58 cents a piece (shipping is more than the item cost LOL). (P12411-ND .27400 5.48 T: CAP 220UF 35V ELECT FM RADIAL: SCHED B: 853222)

I'm not planning on any excessively long battery leads right now but when I use my Astro Flight "Whatt" meter I am in the 18 to 24 inch lead range. From the RCgroups forum it appears that the extra capacitors are added as close to the ESC as possible. Since I am not eager to add capacitors to all of my ESCs, I am wondering if I can simply add them to the ESC plug end of of the meter cable. This would have the capacitors removed from the ESC by the length of the ESC to battery plug cable (usually about 3 or 4 inches). I'm definitely not an electrical engineer so, though this seems like this setup would also trap inductance spikes, I am asking for opinions from the folks on this forum who know. I also wonder how many of these capacitors would be a reasonable number to splice in to the cable assuming that this idea will work.

Up until now, I have had no ESC failures using the meter but I only use it a brief time to get a reading and then shut down the motor. I have, however, noted that the capacitors on the ESC do get warm (100+ degrees) when I make measurements.

I do feel that tis better safe than sorry.

Thanks, John

I also have the Astro Whatt-meter. I wonder if it already has internal capacitors inside?

Some other details---I thought I read somewhere that even this sort of extension is ok, but an alternative to adding capacitors would be to simply shorten the meter's cables. I just soldered on the connectors to the existing cable (actually I think I even added an adapter to a Deans Ultra from the connectors that were already present on the meter when I bought it--so mine are even longer than normal!).

Alan Hahn · « **Reply #7 on:** January 23, 2010, 05:21:56 PM »

BTW,
just checked my Astro Whatt-meter---no internal capacitors.

The leads add about 12" to the total length.

John Cralley · « **Reply #8 on:** January 23, 2010, 07:00:49 PM »

Thanks Alan,

You save me from opening my Astro Flight Whatt meter to check for capacitors. LOL

I still need to know if adding a gaggle of capacitors at the ESC connector end of the Whatt meter will be an efficient induction spike suppressor. I'm thinking of using about five 220 uF in parallel.

Alan Hahn · « **Reply #9 on:** January 23, 2010, 07:12:55 PM »

Well, FWIW, I have used my Astro now for some time on CC35, CC45 ESC's and haven't blown anything up yet.

Before going to the effort of adding caps, I'd cut the extra cable length on the Astro. That would save 6" of length.

Jim Moffatt · « **Reply #10 on:** January 23, 2010, 07:13:16 PM »

John
Looking at the web site
http://www.crystalradio.net/cal/indcal2.shtml
The inductance of the leads is directly proportional to lead length.

So a useful rule of thumb would be to first see what value capacitor your esc has on the input. Then if you double the normal lead length, add a second capacitor of equal value. If the total lead length becomes 3 times the original length then make the TOTAL capacitance 3 times the original.

Its likely that the esc manufacturer added some safety margin in their capacitor for potential increase in lead length so this rule may be a little too conservative. But thats better than a blown esc!

Author Topic: Extending Battery Leads (Read 773 times)

Jim Moffatt

Extending Battery Leads

Crist Rigotti

Re: Extending Battery Leads

Mike Scholtes

Re: Extending Battery Leads

Alan Hahn

Re: Extending Battery Leads

Jim Moffatt

Re: Extending Battery Leads

John Cralley

Re: Extending Battery Leads

Alan Hahn

Re: Extending Battery Leads

Alan Hahn

Re: Extending Battery Leads

John Cralley

Re: Extending Battery Leads

Alan Hahn

Re: Extending Battery Leads

Jim Moffatt

Re: Extending Battery Leads