If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
ScotchTapeLord said that you're alright with 1meg 1/8w and made all the math...
It's mostly dependant on the leakage resistance of your capacitors. Without knowing that you don't really know if the resistors will be overkill or not.
On some fast math, the 36k 10W ones leave room for a 600V max voltage. The 33k leaves for 480V and the 30k one for 548V approx.
Just orientative math.
Also, take into account they're wirewound type and want it or not they have an intrinsec inductance, and will probably add an inductance aswell, that's gonna lower current on the circuit too.
Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
Sir Fixalot wrote ...
Alrighty then! If you guys think that the 1 megohm 1/8 watt resistors will work safely as balance/charge equalizers, then I'll get some asap.
No, I was just saying that 1/8 watt would be okay if you used 1 megohm resistors, and that you could determine the wattage rating needed with simple math.
Put an ohmmeter across each capacitor that can measure 10 Megohms and wait for it to stop changing (this could take a while). If every capacitor exceeds 10 Megohms then you can use 1 M resistors. If the resistance is lower, you'll want to choose a resistor that is about 10x lower than what you read for the lowest capacitor you have. Lower resistance will equate to better balancing but more losses, which means higher wattage rating. I don't recommend charging these to their absolute highest voltage unless you have confirmed that the voltage division is acceptably even through simple resistor combination analysis.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Sir Fixalot wrote ...
Klugesmith wrote ...
My recommendation, which also saves resistors: Form all 8 capacitors in parallel for a while, then measure them individually & make two groups of four to dividing total C in half, as closely as possible. Each group of 4 is wired in parallel, with one bleed resistor. The two groups are connected in series.
The reason I don't want to do that is to keep the ESR Low-I would much rather do sub-banks of 2 in series.
The ESR of the 2S4P bank is exactly the same either way: half the ESR of a single capacitor. Assuming your wiring resistance is relatively negligible, which is not hard to do.
Saz43 wrote ...
Jasonr wrote ...
BE CAREFUL!!!! it will not really matter the leakage of the caps. it is more the body style of the resistors i=v/r and then p=iv those little 1/8 guys will be smoking hot! plus if memory serves 1/8 watt is only good to 150volts?
Jason
I've used 1/8 watts up to 400V with no problem.
ScotchTapeLord wrote ...
Hm? Obviously a 1 M ohm, 1/8 watt resistor can tolerate 350V. P = V^2/R or I^2*R using V^2/R .125 Watts = V^2/(10^6 ohms) V^2 = 125000 Volts^2 V = 353.553 Volts
having 350V across it is the only way to get the wattage that high! Just do math to determine what wattage you need for your application.
I think STL is missing something. Along with the power rating, all resistors have a voltage rating (which also depends on the body size and type). For very high R values, the voltage rating is the more restrictive. For example: the power calculation formula suggests that a 10 megohm 1/8 watt resistor could withstand 1118 volts. Not a good idea. Ordinary small axial R's have voltage ratings in the hundreds (check the data sheet).
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
ScotchTapeLord wrote ... It's very possible I'm missing something...
But in the case of a 10 megohm 1/8 watt resistor, how can you get 1/8 of a watt of dissipation across 10 megohms besides putting 1118 volts across it?
It's a semantic thing. The power spec does not say the resistor -can- dissipate 1/8 watt. It says the resistor will not overheat if the average power is kept below 1/8 watt. That statement is true for all R values in the 1/8-watt series.
Conversely, suppose the voltage spec is 300 volts for that resistor series. It does not imply that a 1000-ohm 1/8-watt resistor can long withstand 300 volts.
[edit] Here's one datasheet. For the 1/8 watt size, "maximum working voltage" is the lesser of 250 V and sqrt(P * R). For 1/4 and 1/2 watt the corresponding limit is 350 V. Most models in that datasheet have an "overload voltage" spec twice as high.
Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
Klugesmith wrote ...
Conversely, suppose the voltage spec is 300 volts for that resistor series. It does not imply that a 1000-ohm 1/8-watt resistor can long withstand 300 volts.
But you can have peak voltages of 300V while having 1/8 watt RMS dissipation, while in the case of the 10Meg you can't have 1/8 watt unless you meet or exceed 1118V...
But I guess I'll have to submit to your point. It's unfortunate that the wattage rating refers more to the size than actual electrical capabilities, though.
Registered Member #167
Joined: Mon Feb 13 2006, 06:41PM
Location: Waterloo, WI
Posts: 54
ScotchTapeLord, Look at the data sheet for the resistor you are choosing is all I am saying. In 1/8 watt almost everyone one I see is only good to 150-200volts. This has nothing to do with ohms law but how the resistor is built! you will notice they have a working voltage of 200 for 1/8 watt. So you must have been really lucky putting 500 volts on them. I would put 2 500k 1/4 watt in series for the extra pennies it would cost and the added safety is priceless.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.