New Accessory Batteries

[KSagal]

I recently got a good buy on some Radio Shack rechargable batteries and was looking for info...

What I bought were Nickle-metal rechargable packs. They were for a toy car, and rated at 9.6 volts, 1600 mwh.

Now, upon examination, there were 8 aa sized cells, each producing 1.2 volts. This is standard. The 1.6 whatt hours I have a question about.

I saw new batteries on the shelf, aa sized and the same metal configuration, rated at 1.2 volts and 2 whatt hours. What is the determining factor here?

What I did, since I bought these discontinued battery packs (Normally $25) for $10 a set. I took one apart, and by adding 2 cells to the remaining packs, I now have packs of 10 cells, producing 12 volts. I will run all four packs parrallel, to give the 12 volts more whatt hours.

I suspect my calculations are accruate. I would be looking for input as to how this should add up and compare with the 5 whatt hour lead acid battery I am replacing. Will I get longer life, longer cycle life, etc...

I do have a lot of lights, and have never tested their draw, but I have always several hours on each charge of the lead acid. I have never had a full charge on it and had the lights go out while I could still glide...

Karl Ian Sagal

Each road you travel should be just a bit better for having had you pass.

[terryp]

Watt do you mean "whatt hours"? ;)

Seriously, it may not be a good idea to parallel the packs, as they're likely to drain each other. It would be better to run individual lights, or groups of lights, off individual packs.

Segway - What's holding you up?

[bystander]

quote:Originally posted by KSagal

I recently got a good buy on some Radio Shack rechargable batteries and was looking for info...

What I bought were Nickle-metal rechargable packs. They were for a toy car, and rated at 9.6 volts, 1600 mwh.

RS has cat #23-331, 9.6v 1600 mAh (rather than mwh)
The typo for w rather than A is significant, in this case the difference would be nearly an order of magnitude, due to the pack voltage of 9.6v vs. the cell voltage of 1.2v. In any case, assuming your pack appears similar to this (before adding cells):
http://www.radioshack.com/images/ProductCatalog/ProductImage/23/m23-331.jpg
the wh will be 9.6 volts times 1600 mAh = approx 14.4 wh.
quote:
Now, upon examination, there were 8 aa sized cells, each producing 1.2 volts. This is standard. The 1.6 whatt hours I have a question about.
if the 8 cell pack was 1.6 wh, each cell would be one-eighth of that, or 200 mw each - a rather low figure for something as large as an AA battery.quote:
I saw new batteries on the shelf, aa sized and the same metal configuration, rated at 1.2 volts and 2 whatt hours. What is the determining factor here?
Again mAh has probably been confused with mwh. I think you'll find those cells are rated in mAh and not mwh. Are we talking about Cat # 23-528? http://www.radioshack.com/images/ProductCatalog/ProductImage/23/m23-528.jpg 2000 mAh AA 1.2v cells cost a little more to make than 1600 mAh cellsquote:
What I did, since I bought these discontinued battery packs (Normally $25) for $10 a set. I took one apart, and by adding 2 cells to the remaining packs, I now have packs of 10 cells, producing 12 volts.
Each pack of 10 cells should be approx. 19 wh (12v times 1.6 amp-hours)quote:
I will run all four packs parrallel, to give the 12 volts more whatt hours.
Mega pack of 40 cells should be approx. 77 wh (4 times 12v times 1.6 amp-hours)quote:

I suspect my calculations are accruate. They seem to be adequate, if my suspicions about your existing battery prove true. However, the calculations may not be accurate. <grin>quote:I would be looking for input as to how this should add up and compare with the 5 whatt hour lead acid battery I am replacing. Will I get longer life, longer cycle life, etc...
Well, if your 5 wh 12v lead-acid battery is actually rated at 5 Amp hours, it's actual wh would be 12v times 5 ah = 60 wh. So your new mega pack NiMH would be about 28% higher capacity. If your existing lead-acid battery is really 5wh then the new battery would have over 15 times the capacity - an unlikely result.

If you could post the approx. dimensions and mass of your 12v lead-acid battery, I could tell it's "ballpark" ah and wh figures.

In addition, NiMH allows deeper discharge (without long term damage) than lead-acid, but if you've only deeply cycled the lead-acids a relatively few times, you won't have noticed their reduced cycle-life.

To keep lead-acid batteries working for their intended cycle life, one should seldom draw more than 20% of total capacity out before recharging again. On a 5 Ah battery, that means 1 Ah, or 1 amp for 1 hour, or 1/2 amp for 2 hours, etc.quote:
I do have a lot of lights, and have never tested their draw, "Testing draw" is done with a DC ammeter, then that figure is multiplied by the voltage figure (measured by a DC voltmeter) to determine the wattage figure. DC wattage is not commonly measured by a single instrument with a single reading. Perhaps this is why it is possible to be confused by the difference between wh and ah.quote:but I have always several hours on each charge of the lead acid. I have never had a full charge on it and had the lights go out while I could still glide...

Karl Ian Sagal

Each road you travel should be just a bit better for having had you pass.

mwh and mAh are somewhat equivalent when one is discussing a voltage around 1 volt, 1.1v 1.2v, etc. When discussing packs of cells where the voltage is much higher, mwh and mAh are not comparable.

Please take these thoughts as advice only. Feel free to use google to confirm or dispute these findings.

P.S. terryp got in a post before I finished this one. You are using a fuse or circuit breaker aren't you? You also might want to discharge the packs before assembling them together (or if already assembled, discharge them in future before working on them). A friend of mine once received a painful burn while (mis)handling a toy RC pack when it inadvertently shorted out on a metal tool he was using.

I've read on Trevor Blackwell's site (http://www.tlb.org/scooter.html) that strings of cells may need some bridge rectifiers to avoid charging issues.

[citivolus]

One thing to keep in mind is that batteries of different Ah ratings have different recharge life cycles. As a guideline, higher Ah results in a lower number of recharge cycles with all other things being equal. You need to be careful to not produce a reverse charge as the batteries age.

On a side note, I came across a charger/reconditioner that might be worth investigating. One version comes with a usb port for monitoring the process.
http://www.dugganbergeronindustries.com/news/view.php?news_id=1

--
swiftly flying

[bystander]

quote:Originally posted by citivolus

One thing to keep in mind is that batteries of different Ah ratings have different recharge life cycles. As a guideline, higher Ah results in a lower number of recharge cycles with all other things being equal. You need to be careful to not produce a reverse charge as the batteries age.

On a side note, I came across a charger/reconditioner that might be worth investigating. One version comes with a usb port for monitoring the process.
http://www.dugganbergeronindustries.com/news/view.php?news_id=1

--
swiftly flying
Uhh.. That one does two AA batteries at a time, I beleive KSagal indicated he had 40 in his mega pack.

However, they seem to be selling the USB model for the plain model price until the end of August.

Nice idea though, if you only have a couple of AAs to maintain.

I was under the impression that "recharge life cycles" were diminished by discharging over the maximum "C" or charge rate specified by the manufacturer. Some batteries have higher "C" rates designed into them, and can deliver more amps in a shorter time. Such batteries can be more costly. Although mah capacity is often printed on AA, AAA, C, & D sized rechargable cells, the "C" rate can sometimes only be found on the cell's specification sheet.