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Re: Battery power for big SSTC



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