when will they ever learn?

[Murflynn]

 

 

 

6 Trojans in a 12 volt bank so a bit of series and a bit of parallel, surely the best of both worlds.

 

...............Dave

you can't ignore voltage when stating the amp-hour capacity of your batteries.

to look at it another way, four 100AH 6volt batteries could have a total of 100AH at 24v or 400AH at 6v.

 

thanks WotEver for pointing out my carelessness

Edited February 20, 2016 by Murflynn

[WotEver]

four 100AH 6volt batteries could have a total of 100AH at 24v or 400AH at 24v.

Huh?

 

T.

[cuthound]

Huh?

T.

4 x 100ah 6v batts in parallel = 400ah.

 

4 x 100ah 6v batts in series = 100ah?

[Loafer]

4 x 100ah 6v batts in parallel = 400ah.

 

4 x 100ah 6v batts in series = 100ah?

 

That is all true. However it isn't what Murflynn wrote (although I think he only made a trying error). Look more closely at his voltages!

Edited February 20, 2016 by Loafer

[cuthound]

That is all true. However it isn't what Murflynn wrote (although I think he only made a trying error). Look more closely at his voltages!

4 x 6v in series = 100ah @ 24 v.

 

4 x 6v in parallel = 400ah @ 6v.

 

That ties in with what Murflynn wrote (I think).

[Loafer]

Nah. He wrote 'four 100AH 6volt batteries could have a total of 100AH at 24v or 400AH at 24v.

 

Can't be both!

[cuthound]

Nah. He wrote 'four 100AH 6volt batteries could have a total of 100AH at 24v or 400AH at 24v.

 

Can't be both!

Ah, i see he edited at 5:12pm. (Before I read it and presumably after you read it - hence the confusion).

[Loafer]

Ah, i see he edited at 5:12pm. (Before I read it and presumably after you read it - hence the confusion).

 

Sorry. I didn't notice his edit! My quote was from post no 252 by Wotever!

[WotEver]

4 x 6v in series = 100ah @ 24 v.

 

4 x 6v in parallel = 400ah @ 6v.

 

That ties in with what Murflynn wrote (I think).

Look at what he wrote originally (in my quote)

[ditchcrawler]

 

some of the earlier OC71's may have painted black but the later ones and the OC72's and OC 73's had a metal case but if you carefully teased it off you found a glass case underneath (no paint scraping required ) OC44's and OC45's were better choices they were always painted

 

eta yes indeed it was true , the "proper" photo transistor was the OCP71, an OC71 with clear gel as opposed to the normal opaque white filler which made it more sensitive

I had forgotten all this stuff. Made a rev counter with an optical transistor in the end of a Biro pen

[Theo]

 

 

when you are measuring a capacitor if a 2 lb jam jar is one jar is a 1lb jam jar 1/2 a jar ?

Are you talking about Leyden Jars?

[John V]

digging back into valve circuits from the 20's when valves were expensive and re-cycling the designs as transistor circuits (for the same reasons) reflex and regenerative and combinations.........fascinating stuff for schoolboys !!!

[Theo]

 

Surely a capacitor is a charge store whilst a battery is an energy store?????

 

And we are very comfortable talking of the charge stored in a capacitor and that must discharge at a variable voltage!

 

This is why the amp-hour is a "measure of convenience" ... because we don't need to think about voltage.

 

............Dave

I wouldn't say that. Capacitors store energy too. E=I/2CV²

[dmr]

I wouldn't say that. Capacitors store energy too. E=I/2CV²

 

I was only playing with Nick but I think he's lost interest, or else gone away to work on a very clever reply.

 

..................Dave

[Batavia]

Are you talking about Leyden Jars?

Probably yes.

 

A Jar was a unit of capacitance used by the Navy - 1 Jar = 1111 pF. Mentioned in my 1938 Handbook of Wireless Telegraphy, I seem to recall.

 

Chris G

[John V]

Are you talking about Leyden Jars?

 

yup ! they were the first capacitors my Admiralty 1912 handbook for telegraphists (no longer have it because some b@rstard nicked it)

 

the wireless sets (heh heh heh) used capacitance measured in "jars" ....I believe the standard actually was a 2lb jam jar with foil glued on the inside and out (up to the commencement of the curve to the neck).

The fascinating thing about the handbook was the incredible sophistication (even at that date) of the aerial systems, nearly all the types of aerial for (then) normal frequencies including goniometers and the Bellini - Tosi system of direction finding. It was given to me about 1956, it sparked a strong interest in radio and lead eventually to my career path

 

eta (sparked).....sorry

Edited February 21, 2016 by John V

[Batavia]

From my trusty HWT, a Jar is defined as being equal to 1,000 centimetres, where 1 centimetre is the ESU unit of capacitance - presumably a "standard" Leyden jar comes somewhere close to this.

 

A normal centimetre as a unit of capacitance doesn't sound dimensionally correct - need to check this, but I haven't used ESUs and EMUs since A levels (thank goodness)!

 

Chris G

[Murflynn]

I didn't believe you, but you are quite right!!

 

https://en.wikipedia.org/wiki/Centimetre

[Loafer]

Blimey. I thought I new everythink when I remembered Leyden Jars.

 

Didn't know about the centimetre thing! \\\humble\\\

[John V]

never mind don't think I knew it.....I'm blxxdy certain I never knew it !!!

[WotEver]

Never heard of it here.

[nicknorman]

never mind don't think I knew it.....I'm blxxdy certain I never knew it !!!

I makes absolute sense dimensionally. A capacitor has plates, which have area. More area = more capacitance. So there is cm squared on top. Another thing affecting the capacitance is how close the plates are together. The smaller the seperation of the plates, the more capacitance. So the separating distance goes on the bottom. So you have an expression for the capacitance which is some constant (dielectric etc) multiplied by the area (cm squared) divided by the seperation (cm). Dimensionally you therefore have cm squared divided by cm = cm.

 

Bigger plates further apart, or small plates closer together, have the same capacitance so the capacitance can just be expressed by a (dielectric) constant x distance (cm).

 

Simples!

Edited February 21, 2016 by nicknorman

[Loafer]

I makes absolute sense dimensionally. A capacitor has plates, which have area. More area = more capacitance. So there is cm squared on top. Another thing affecting the capacitance is how close the plates are together. The smaller the seperation of the plates, the more capacitance. So the separating distance goes on the bottom. So you have an expression for the capacitance which is some constant (dielectric etc) multiplied by the area (cm squared) divided by the seperation (cm). Dimensionally you therefore have cm squared divided by cm = cm. Simples!

 

Yes, your Worship!

Actually, having read it again, it reads well-pukka. Units, units!

 

cm² div by cm = cm. Fantastic.

 

Green, for a good reminder of 1974 'A' level stuff.

[nicknorman]

Dimensional analysis is such a powerful but simple tool for "gross error checking" - it's a pity most people don't seem to know what it is (maybe it sounds too Dr Who?). It would certainly put paid to talk of "amps per hour"!

[John V]

Salaam sahib, I grovel before your magnifiscence

Edited February 21, 2016 by John V