Why did this happen - Page 1
Forum section: electronics / beginners

author: shane_95
author_rank: Regular Contributor
timestamp: July 03, 2012, 09:31:40 am
content: I had three 9v battery's wired up in parallel to get a 27v out put to run some LEDs. I disconnected the LEDs to do some soldering on them, after a bit BANG out of the 3 battery's 1 had exploded, 1 was going to go very soon, and the last one was starting to melt. Why was that?

author: T4P
author_rank: Super Contributor
timestamp: July 03, 2012, 10:02:21 am
content: Accidental shorting?

author: Wilkins
author_rank: Contributor
timestamp: July 03, 2012, 10:03:35 am
content: If you want 27 volts you should wire your batteries in series.Check your battery terminals for shorts, you can do this with the continuity setting on your multimeter, if you don't have a multimeter i would highly recommend picking one up from jaycar, a cheapy one will cost ~$10.

author: shane_95
author_rank: Regular Contributor
timestamp: July 03, 2012, 10:11:36 am
content: Dad did see the red and black wires joining at one point so im thinking short

author: rsjsouza
author_rank: Super Contributor
timestamp: July 03, 2012, 10:21:13 am
content: That's what I was going to say... If you connected the positive/negative of two batteries to the negative/positive of the other one, you were in fact having 18V across your short-circuit. The battery that exploded was probably the one that was inverted, as it was taking twice the load of the other two.To have 27Vdc you need to connect the negative of one battery to the positive of the other one, but keep in mind to always leave one positive and one negative floating (or you will have a bigger boom with 27V short-circuit)Something like what is shown at this link:http://www.instructables.com/id/How-to-make-a-27-Volt-Battery-out-of-three-9-volt-/step5/Power-whatever-you-want/

author: Wilkins
author_rank: Contributor
timestamp: July 03, 2012, 10:30:33 am
content: I would recommend using a >330 ohm resistor over a 20 ohm if you are intending to run 10 leds off 27v, that is unless you want them to smoke.

author: Rerouter
author_rank: Super Contributor
timestamp: July 03, 2012, 11:24:03 am
content: heh, me thinks no one watched the video,he had 3 batteries connected in parrellel (thats 9V still shaun) for 27V they would need to be in series,as to why they all took a beating, my best guess is either,1. red and black shorted2. one of your batteries was furthur discharged than the others, and had the other 2 forcing charge into a non rechargable battery chemistry,

author: shane_95
author_rank: Regular Contributor
timestamp: July 03, 2012, 12:48:50 pm
content: Quote from: Rerouter on July 03, 2012, 11:24:03 amthe 31 views say's other wise

author: IanB
author_rank: Super Contributor
timestamp: July 03, 2012, 02:14:42 pm
content: Quote from: shane_95 on July 03, 2012, 09:31:40 amI thought you misspoke perhaps, but according to the video you really did have them wired in parallel. Wiring in parallel will not give you 27 V, it will give you 9 V.Now an important thing about wiring in parallel is that all your batteries must be equal--they must all be equally fresh and unused so they are balanced with each other. If you connect one used battery in parallel with one or more fresh batteries you will have trouble: the fresh batteries will try to charge the used battery. Since alkaline batteries are not designed to be charged, the battery being charged will probably leak or even explode as you saw. Also the batteries doing the charging will possibly deliver so much current that they themselves will get warm or hot.

author: shane_95
author_rank: Regular Contributor
timestamp: July 03, 2012, 02:37:26 pm
content: Ok got ya. parallel = same voltage, series = voltage multiplied

author: Hideki
author_rank: Frequent Contributor
timestamp: July 03, 2012, 02:45:32 pm
content: series = voltage addedYou can for example connect 9V in series with 1.5V to get 10.5V.If you flip the connections around on the 1.5V battery it will have to be subtracted instead of added. 9V - 1.5V = 7.5V

author: amyk
author_rank: Super Contributor
timestamp: July 04, 2012, 08:50:03 am
content: How much current were you pulling from them? 9V batteries have very limited current capacity.Alkaline chemistries generate gas if discharged too quickly, and that can cause them to explode.

author: Wim_L
author_rank: Regular Contributor
timestamp: July 04, 2012, 08:55:07 pm
content: And that's particularly easy to see when someone gets the idea that the best way to store two 9V batteries is to clip them together. It's a perfect fit! They self-destruct fast.