Hi, I have connected 5 new NiMh batteries in series, each is rated at 3800 mAH. When I connect a 10W, 6v halogen bulb to them it lasts about 2 hrs. I expected longer than this, calculating that the current should be 1.6 amps through the bulb, and the battery pack should have 5 x 3.8 Ahr = 19 Ahr. Should the bulb not last for 11.8 hrs, or am I doing something wrong? Rod
You are indeed doing something wrong.
In series, you have 5 x 1.2V (nominal) = 6V 3.8Ah (you multiply the current rating in parallel, not in series).
So you have 6V x 3.8Ah -> 22.8 Watthour (very roughly). A 10W bulb will last about 2.28 hours (this is very simplified as the terminal voltage will change during discharge).
So your experimental result (2 hours) agrees quite closely with the calculation.
Cheers
PeteS
** Yes.
The " Amp Hour " rating of a *series connected* pack depends on the individual cell's capacity - it does not matter how many cells there are. Using more cells increases the Energy capacity - that is specified in " Watt Hours " .
In your example, the pack has the same 3.8 AH capacity as each cell BUT the Energy Capacity is now 5 times that of one cell.
For one cell:
1.2 volts x 3.8 amps = 4.56 Watt Hours.Or 22.8 Watt Hours for the 5 cell pack.
....... Phil
No. Pretty well as expected. (Batteries are 'newish' by the sound of it)
So you have 5 batteries connected in a series string. (5 x 1.2) = 6 volts. Then you connect one single 10 watt bulb (6 volt) across the string 6 volt string. The bulb will draw 1.6 amps through all the batteries in the string until they are discharged. The string of batteries will be able to provide 3.8/1.6 = 2.375 hours of current.
Note:In practice; since discharging any battery that quickly you would most likely get somewhat less than the theoretical 2.375 hours even with new batteries. And probably a shorter life. Whereas if it was much lower discharge, say one quarter of one amp you might get considerably more than a theoretical 3.8/0.25 = 15.2 hours! And longer life; provided batteries are recharged correctly.
By the way this must be a troll?
Also BTW: A friend told me that he had an old 12 volt car battery* (probably 60 amp/hours when brand new many years before) that had been condemned for engine starting. Gave it a quick charge and took it to a summer cabin. It then ran a small 12 volt AM/FM car radio every weekend for many, many hours during a whole summer/fall.
Together we calculated something like this; Worn out battery with say (at slow discharge) perhaps 30 amp.hrs. capacity? Small transistorized car radio say using 100 milliamps. Thus 30/0.1 = 300 hours. (Well even if the radio had used 0.25 amps (250 milliamps) that would still be 30/0.25 = 120 hours! probably enough for 10 hours of use for
12 weekends )In a 12 volt car battery six, nominally 2 volts each, cells are already connected in series. So, like the 3.8 amp.hr. cells in this OP they also discahrage in series.
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