Battery Pack Questions
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I am currently using a set of 10 NiMH C cells to provide power for a robot that I am working on. I purchased this pack from a vendor pre-assembled into nice pack with heat shrink wrapping and just two wires coming out. 10 cells in series = 12.5 volts under load. I want to increase the capacity of my battery pack and have a few questions that I hope someone can answer.
The primary question is: Can I get a second 10 Cell NiMH pack and permanently wire it in parallel with the first pack? (Two sets of 10 cells. Each set of 10 wired in series and the two sets are in parallel)This will produce the same voltage but twice the capacity. Other questions are: Will my NiMH charger have any issues charging them while wired in parallel? Will this affect the life of the batteries? What other consideration should I take into account if I do this?
Thanks.
The primary question is: Can I get a second 10 Cell NiMH pack and permanently wire it in parallel with the first pack? (Two sets of 10 cells. Each set of 10 wired in series and the two sets are in parallel)This will produce the same voltage but twice the capacity. Other questions are: Will my NiMH charger have any issues charging them while wired in parallel? Will this affect the life of the batteries? What other consideration should I take into account if I do this?
Thanks.
Comments
I Mis matehced my cells and I the one pack is draining the other pack .
so I have spent the last few days cycleing them to force them to be nice.
your main issue IS going ot be charging ..
what kind of charger do you use ?
EDIT:
If your charger is a dumb charger it may just work .
but some of the funky ∆V and ∆T chargers may get cranky with a weird impedance across them .
1] Yes, you can wire the in parallel for extended use without any problems.
2] Chargers are limited in output, and at best you may have to wait twice as long to charge the doubled capacitity. But other issues evolve that begin to get complex. Ideally, if the charger was mated to the original battery pack, it would be best to charge each unit individually on a swap out basic.
Chargers are not just voltage supplies, they provide amps as a predetermined rate (have an overall power rating of peak amps or watts). Batteries have preferred rates of charge and either exceeding the rate or falling far below the rate can produce bad effects. To make matters more awkward, many battery manufacturers are happy to have you use a bad charger and buy more batteries.
And finally, the 'ideal unit' for charging a battery is an individual cell. A series of 10 NiCads or NiMhs can have an individual cell fail, reverse polarity and mess with the whole unit. Similarly imbalances in parallel can put the whole works into a tail spin. And a combination of the two in failure will offer the opportunity you to realize what an indeterminate failure really is.
I suggest that NiCD and NiMH are good solutions, but you might as well buy individual cells and larger holders. In the usual situation you can recharge the whole, but when trouble comes calling you can test and charge individual cells until you sort out the 'bad apples'.
BTW, having extra charging capacity on a charger at a rated voltage can become a hazard rather than an asset. Recently my 30AMP 8VDC gel cell charger nearly explored a 4.5AH 8VDC and self-destructed in smoke and flames. In other words, the charger should match or be smaller than the battery pack for the sake of safety. And if unattended, leave it in a fire safe place or create an automated shut down for overheating of the battery and the charger.
This may all sound extreme, but safety is important and people tend to mindless mix and match chargers with battery packs of questionable compatiblity.
My goal is to be able to perform routine charging of batteries without having to remove them from the robot. To do this, I would either need to charge both banks at one time or build some sort of bank switching system which I would like to avoid if I could.
Thanks
now youre dealing with thermal stresses too . ans when a Cells Temp changes so does its resistaince to a charge ..
if one pack get hotter it will Draw more then the cold pack making things worse .
at much lower charge rates (C/30) heating is not a big issue. then it its possible to || packs with out too much safety issues
C/10 is considered to be a "trickle" or float charge.
I charge NiCAD and NiMH at C/1 or C/2 all the time.
Rich H
Because you can adj the charging current you just have to have the right charging current so your batteries will fully charge this will be trial and error
http://www.integy.com/16X7-Pro_Page1.pdf
I like these types of chargers
I hope this helps
" the ") " and "0" are on the same key LOLs
Peter
But..........
1. Battery packs in series and parallel are still problematic and should be matched as closely as possible. Different AH capacity on two packs can make the whole scheme go poorly. In other words, when you charge 10 cells at the same time you have 10 times the chances of difficulty over one cell, and when you have 20 cells charged at the same time, you get 20 times the difficulty - unless all batteries are tightly matched to the same level of quality. Laptops have a lot of history of these problems. ONE BAD cell often confuses the charger's intelligence.
2. Having a 10K thermistor connected to a BasicStamp that drives a relay that will shut down the whole show if it gets too hot will make the whole scheme much easier to manage. One 10K thermistor should be attached physically to each battery pack. So actually two thermistors might be used in your case. After all, it is the excessive heat from overcharging that really upsets the chemistry and shortens the battery life. You can argue endlessly about the right charge rate, but too hot is never any good.