Question on how to measure resistance. If you use an ohm meter to
measure resistance, I presume it is using a 1mA or smaller current. In
electronics applications, that's probably fine. But in a situation
where typical current is in the hundreds of amps, will taking a
measurement that way be reliable?
It seems that for low current, you will be measuring more-or-less the
best path through the circuit - in this case from terminal to cable.
That is, there may be small areas with good metal contact and lots of
areas with lesser contact or none. With high current, won't those good
contact areas become overloaded and their resistance increase?
If so, then I presume a better way to measure resistance under high
current would be exactly that: apply high current and measure the
voltage drop.
Anyone care to validate or invalidate this?
Peri
------ Original Message ------
From: "Cor van de Water via EV" <ev@lists.evdl.org>
To: "Electric Vehicle Discussion List" <ev@lists.evdl.org>
Sent: 19-Aug-14 9:15:36 AM
Subject: Re: [EVDL] CALB bolt terminals getting hot -
Martin,
Delivering 300A at 120V is 36,000 Watts, so losing 350W in the wiring
and terminal connections means only 1% loss in the grand scheme of
things.
A single traffic light turning red in front of you so you have to stop
and again accelerate up to speed is likely a bigger difference in the
efficiency of a trip...
Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: cwa...@proxim.com Private: http://www.cvandewater.info
Skype: cor_van_de_water Tel: +1 408 383 7626
-----Original Message-----
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Lee Hart via
EV
Sent: Tuesday, August 19, 2014 9:08 AM
To: Martin WINLOW; Electric Vehicle Discussion List
Subject: Re: [EVDL] CALB bolt terminals getting hot -
Cor van de Water via EV wrote:
Depends on your current. Typically I would say in the order of
magnitude of 0.1 mOhm (milliOhm) because a 300A current will then
give 30mV drop, which produces 300A x 0.03V = 9 Watt of power loss
as heat.
Martin WINLOW via EV wrote:
At EVERY connection? In a 120V lithium pack that 's 38 x 9 =
nearly 350W of heat!
No; Cor has it right. And, 0.1 milliohms is a *good* connection. You
will discover that it is damnably difficult to make a connection that
good with aluminum terminals!
--
You never change things by fighting the existing reality. To change
something, build a new model that makes the existing model obsolete.
-- R. Buckminster Fuller
--
Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm
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