Who knows alot about batteries especially nicads?
rwgast_logicdesign
Posts: 1,464
Ok so ive been trying to work out the power source im going to use in my bot... I have all the regulation and all that good stuff for the circuitry, im just left trying to figure out what to do about the motors. The only spec I have on my motors is 3-6v dc, I have tested them and they seem fine at 9vs, but I don't plan on running them over 8, #1 because my motor controller is 8v input minimum but #2 8vs is the highest voltage I can run them out without them being stupid loud.
So right now im looking at using 3 9.6v RC NiCad bateery pack in parallel and maybe a 9.6v nicad drill motor battery also in parallel. Most books you read never explain battery's all that much, they all say the same thing about how they work on a lower chemical level. There are just somethings I dont understand about batterys which im sure are assumed to be common knowlege. The biggest question i have is lets say you have a battery at 9,6 volts with 2 amp hour rating. Does this means the battery can put out 2 amps at 9.6v for an hour? After use batterys voltages starts to drop, so if im trying to supply 8vs to motors with a 9.6v motor i need to know how long my battery will hold over 8vs.
The next thing is when you series batterys the voltage adds up when you put them in parallel the current adds up. Well when you parallel battery with the same voltage but different amp hours, is everything going to run smooth, I mean its not going to be like power regulators where when you parallel them the the whole loads gets drained from the stronger source and overheats is it? I guess what im asking is, is it safe to run different amp hour rated battery's in parallel especially nicads. Also when batterys are paralleled what happens to the voltage is all the batterys have a slightly different charge, will the voltage output equal the lowest charged battery or what?
Lastly is if I throw all these batterys in parallel can I charge them all hooked up in parallel with the same charger ive been using for singles, itll just take longer? What about paralleling multiple charger outputs to provide a higher amperage. Does anyone know of a good through whole IC for nicad battery charging and management becuase all my chargers stink and will overcharge the battery's which causes alot of "memmory" problems, id like to build a custom taylored chargin system for my bot and either use and A to D and micro for battery managment or maybe a fully intergrated battery managment chip, this sounds like something maxim would probably make
So right now im looking at using 3 9.6v RC NiCad bateery pack in parallel and maybe a 9.6v nicad drill motor battery also in parallel. Most books you read never explain battery's all that much, they all say the same thing about how they work on a lower chemical level. There are just somethings I dont understand about batterys which im sure are assumed to be common knowlege. The biggest question i have is lets say you have a battery at 9,6 volts with 2 amp hour rating. Does this means the battery can put out 2 amps at 9.6v for an hour? After use batterys voltages starts to drop, so if im trying to supply 8vs to motors with a 9.6v motor i need to know how long my battery will hold over 8vs.
The next thing is when you series batterys the voltage adds up when you put them in parallel the current adds up. Well when you parallel battery with the same voltage but different amp hours, is everything going to run smooth, I mean its not going to be like power regulators where when you parallel them the the whole loads gets drained from the stronger source and overheats is it? I guess what im asking is, is it safe to run different amp hour rated battery's in parallel especially nicads. Also when batterys are paralleled what happens to the voltage is all the batterys have a slightly different charge, will the voltage output equal the lowest charged battery or what?
Lastly is if I throw all these batterys in parallel can I charge them all hooked up in parallel with the same charger ive been using for singles, itll just take longer? What about paralleling multiple charger outputs to provide a higher amperage. Does anyone know of a good through whole IC for nicad battery charging and management becuase all my chargers stink and will overcharge the battery's which causes alot of "memmory" problems, id like to build a custom taylored chargin system for my bot and either use and A to D and micro for battery managment or maybe a fully intergrated battery managment chip, this sounds like something maxim would probably make
Comments
So, if you parallel the packs make sure not to run them down below about 1.1V.cell. Actually, that applies even if you don't parallel them.
If you parallel two packs of unequal charge the one with the higher voltage will charge the lower voltage pack.
A 9.6V 2Ah (19.2Wh) pack probably will not supply 2 Amps for one hour. You may be able to draw 19.2 Wh of energy out of it but only if you do so slowly. The faster you draw power out of a battery, the greater the losses.
You can charge them paralleled but it is better not to.
Anyways im having a hard time finding out how many amp hours these batterys are there Tyco no 2998 9.6vNiCad packs for tyco turbo vehicles.... They all have 8 cells in them that are just a bit shorter than AA batterys, im guessing each cell is 1.2v just like a standard nicad, Is there a standard amp hour on most of these RC packs, or the cells in them? The Ryobi drill battery has cells that are much fatter and its 2200mah, the charger for the ryobi is putting out the same voltage and current as the tyco chargers. Now according to what W9 said above im getting that is the tyco packs are not also 2200mah I cant parallel the tycos and ryobi, im not even talking about when charging here im just taling about getting more amp hours
Sub-C size cells are popular in power tools, they also can vary greatly in capacity. 1500mAh was the low end years ago but I took apart a cheap Chinese drill recently to find that they were a pathetic 800mAh! Nowadays you can get NiMH Sub-C cells over 4,000mAH. Sub-C is the size that you see in RC car packs.
So im still unclear as to wether I can parallel the 9.6v NiCad drill cells along with the tyco packs, for operation and when charging. Im guessing the drill pack would have to be charged separately since it needs to be charged longer.... or at least the drill cells need to keep charging after the tycos packs have stoped somehow?
I am sure the answers to most of your questions can be found from this page:
A. Make secondary batteries more fragile to charging and discharging. (so the makers sell more batteries, and special chargers)
B. Never let the public have a generic packaging if it can be avoided. (this they likely learned from Gillette and Schick)
Are you really wanting NiCd or do you want the newer NiMH. There is quite a bit of difference as NiMH is a technology that is advancing and maybe keeping up with Lithium in power densities.
It really doesn't matter what you chooose, the more cells you have in series and parallel, the higher the chance that you will burn one up due to a charging or discharging imbalance. That is the really annoying reality of batteries.
If you want fast easy charging, you might as well buy a system. If you want to DIY, it is best to keep the design simple and go for medium rates of charging.
I have another good link laying around somewhere, but I have misplaced it, however the site may no longer exist for that matter. Anyhow it dealt specifically with designing and building power packs, including tips, tricks, and the math involved. If I happen to come across it, I will post it as well.
Thanks for the thanks.
Bruce
www.batteryuniversity.com
The bottom line about batteries is that they require some idea of what the chemistry is doing. Also, it helps to understand that many of advancements are rather exotic.
The two main enemies of batteries are heat and deep discharge. In general batteries like to be closer to their fully charged state. Leaving a dead cell around tends to deteriorate faster, though some disagree and claim NiCd and NiMH can sit around without charge.
NiCds are good, but the NIMH are much better in terms of capacity. I believe that the NiCds might be better for use in rapid discharge; such as electric airplane flight. But the extra capacity of NiMH make the trouble of managing them a bit more worthwhile for the same use.
Once you get into deciding to go with a battery, the next problem is charge rate. While Lead acid will do well on a trickle charger and maybe even NiCd do well on a trickle charge; the newer chemistries want you to either charge or discharge. But that is merely part of the problem. Lead acid batteries seemed to tolerate a fast charge upon occassion, but new battereis prefer to be first slow charged, then fast charged, and then topped off with a slow charge. This 3 stage charging can be avoided if you provide the right charge rate and make sure your batteries are adequately discharged before charging again.
My own feelings are that NiCds are on the way toward disappearing. I have decided to get rid of any NiCds I have and to switch to NiMHs. I am still frustrated by Lithium batteries as I have just had enough new or nearly new batteries fail to resent the fact that they are so expensive.
As I see it, all cells comprising a "pack" (whether series, parallel, or any combination) should be of the same rating and from the same manufacturer - and especially in a charging situation.
It may be that some kinds of batteries are easy to build as uniform cells and others are more difficult. I suspect that Lithium may be one of the more difficult. NiMH uses rare earths coating the anode of the battery that are both expensive and very thin. That kind of technology may make uniformity harder and certainly causes them to be a bit more fragile.
About once a year, I find myself having to re-read material published about batteries. In the beginning, new technologies tend to claim to have resolved problems. But as time goes by, problems become more obvious. So, literature from manufacturers may not always be truthful about battery performance.
Every battery maker wants to sell more batteries and there are only two ways to do so - sell better batteries OR make batteries that don't last long. So battery makers sell higher and higher capacity (or claim to) and faster and faster charging (which damages the batteries more).
If you want rechargible batteries to last long, you need to find the best charge rate and sometime you have make sure you have them discharge enough before you charge. So these days, fancy chargers that may even discharge the battery before charging are required to get the most.