Re: Battery power for big SSTC

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Harold Weiss" <hweiss-at-new.rr-dot-com> 

Hi All,

On cable for batteries, if you are going to try running at 200-400 A, for
any length of time, you will need 2-4/00 cable.  The thin stuff they use in
cars is ok for the amount and length of time of the high current, and won't
heat much.  But if you tried to use >5' at the usual runtime of a coil, the
cable will melt.

David E Weiss

 > Original poster: davep <davep-at-quik-dot-com>
 >
 >
 > >Actually, you can probably pull a lot more than 60A from that 60Ah
 > >battery...
 >
 >          Just So.
 >          If 'usual automotive battery' 600 A or so is possible,
 >          maybe more.
 >          The 60AH is 60Amps for One Hour.  On Paper that means
 >          3600Amps for one minute, if the load 'asks' for it.
 >          In reality the math is not THAT easy, and physics is more
 >          complicated and the WIRING to handle even 200A is
 >          nontrivial.  cf below.
 >
 > >200A wouldn't be unusual...
 >
 >          My motorcycle uses a _15AH_ battery for starting.
 >          The _spec_ current for the starter on this 15AH battery is
 >          200A +.
 >          I've measured it.  (yes:  I have such a meter...  8)>>)
 >          It GETS 200A.
 >          Automotive starters are more potent yet.
 >          (yes: this is all '12v'/)
 >
 > >you'd have to watch the heating of the battery, though.
 >          And the 'wires'.
 >
 >          Something 3/8 dia or so.  Larger if longer.
 >          Alligator clips ('jumper cables') are Real Iffy.
 >
 >          (I'll assume someone has wire tables to assign the necessary
number
 >
 >          of 'oughts' to the cable.)
 >
 >
 > >If the batteries are engine starting types (car batteries), then they're
 > >designed for 100% duty cycle at a low current (20 hour discharge) and for
 > >infrequent gargantuan current (starts at 300A+, but perhaps 30
seconds/hour
 > >duty ).
 >          Or more...
 >
 >          8)>>
 >
 > =====
 > >>Inspired by Dan's 10kW SSTC, I was wondering if anyone considered car*
 > >>batteries** as a power source for larger SSTCs?
 >
 > >>I am able to get batteries which are not quite good enough to start an
 > >>engine but can nevertheless hold a charge, for free.  I use a bank of
 > >>four to run an ex-telecomms inverter - can give 300W for several hours.
 >
 >          (I use one 'discarded' motorcycle battery to run my
 >          _electric_ lawn mower.  8)>>)
 >
 > ...
 >
 >
 > >>A 60Ah battery can deliver 60A for an hour when new.  When old, we can
 > >>probably still get 60A, just not for so long.
 >
 >          Some yes, some no.  There are varied failure modes.  Part of
 >          setting up such a bank would be to check each candidate,
 >          under load, to see how it will behave.
 >
 > >>If we hook up twenty of these 12V batteries, we have 60A -at- 240V = 14.8kW
 >
 > >>to play with. (Yikes!)
 >          Even at 60A, mind the cabling.  Yes.  It should/will
 >
 >          work.
 >
 >
 > >>* Automobile for those in the USA
 > >>** I should really call them accumulators.
 >
 >          ... if used on a valve excited coil.
 >          8)>>
 >
 > --
 >          best
 >          dwp
 >
 > ...the net of a million lies...
 >          Vernor Vinge
 > There are Many Web Sites which Say Many Things.
 >          -me
 > ...for he has read everything, and written nothing...
 >          A J Raffles
 >
 >
 >
 >