TexAg78

I have a 150 mA wall wart, and I want to use it as a C/10 charger for three Sanyo 1450 mAh, 4 cell NiMH receiver packs. Since the packs have the same manufacturer and capacity, can I connect two in series and charge them on the 9.6V side while I charge the other on the 4.8V side?

exeter_acres

My Feedback: (2)

theoretically you probably could...but unless you KNOW that they are all exactly matched....which you don't... it probably won't work... it will overcharge some cells while undercharging others......

either charge them one at a time, or invest in a better charger so you can charge multiple packs at the same time....

just my .02... adjusted for inflation

JNorton

My Feedback: (2)

Just don't do it. Take the advise Exerter gave you and charge one pack at a time. I guarantee you will ruin NiMh or NiCd packs if you charge them in series.
John

laryboy

My Feedback: (2)

can you explain why it is not ok to charge 8 batteries in series

JNorton

My Feedback: (2)

Larry Boy,

Wasn't talking about charging 8 individual batteries in series that are used together in a pack. Then all the batteries will have the same discharge and will charge back up together fine.

What I meant was that you should not take two packs that were used separately, have different discharge levels and not expect to have 4 cells over charged or undercharged. Do this for a couple of cycles and the packs imbalances would get greater until a cell or two reverses. Granted charging them at a C/10 rate that is usually used to balance a pack would help but in good conscience would you recommend someone do it? Perhaps I was a bit strong saying I'd guarantee the packs would be ruined but would you do it with your own packs? I wouldn't.

John

laryboy

My Feedback: (2)

norton.....................your theory sounds right but i never heard anyone say that if you have a 8 cell pack and 4 cells go bad ,you can not replace the 4 cells with new ones because you dont know their discharged status. what about that?

JNorton

My Feedback: (2)

LaryBoy,
First I really don't know anybody who replaces 4 cell out of an 8 cell pack.

But I'll answer this way. It is not the first discharge status so much as it is the subsequent cycles. If you charge separate packs in series the cells won't balance. If you replace the cells in an 8 cell pack all the cells will then be subsequently discharged at the same rate and charged together. The key is that the cells are used together. If you do put new cells in an old pack I would certainly then charge them at a C/10 rate and discharge them for several cycles until I started using them. I would also take a voltage reading of each individual cell to make sure of their balance.

John

xkwizt

too risky to do a custom job like that, just invest a new charger, 20 bux (aussie) which is about 15 US u can get a split charger that does 200mah

TexAg78

I appreciate the feedback. Not to beat the subject to death, but what if I discharge both packs prior to charging them (using the same discharger, settings, etc.,) so they are at the same level? I seems to me like a C/10 charge rate is tame enough to where I shouldn't have any problem if the initial pack voltages are the same. The current through both packs would be the same, so they should charge at about the same rate, so if they start at about the same point they should end at about the same point.

JNorton

My Feedback: (2)

Just on general principles like dragging finger nails across a chalk board I don't like the idea. But I see no reason why it wouldn't work.

JPMacG

My Feedback: (2)

In my opinion the answer to your question is yes. It should be fine to charge the two 4.8V packs in series on the 9.6 volt charger lead of your wall wart, and there is no need to discharge the packs first. You are using a C/10 charger and there will be no damage to the packs if one of them is overcharged for a short time. Just be sure you get the polarities right.

Parallel is another story. It is almost always a bad idea to charge packs in parallel.

Rodney

I rarely dissagree with Mr. Norton but this time I will. Since you are charging at approximately C/10, you can safely charge these batteries in series and even leave them on charge for 24 hours with no problems, in fact probably do the cells good as it will equalize the charge since the ones charged first will not be seriously overcharged (the chemical recomposition during the slight overcharge is well within the limits of that size cell at that rate). After 24 hours all cells should be at maximum capacity.

JNorton

My Feedback: (2)

Hey Rodney we can't all be perfect. I know I'm not.

I will say that if the charge rate is above C/10 don't do it.
I still won't. I don't like getting involved in practices that could create bad habits.

Another idea is to get a Super Digipulse. It will charge 6 packs at once.
http://www.ehobbies.com/1004-6287.html

John

GeraldRosebery

My Feedback: (14)

Really bad idea. Unless the two series packs are very close in voltage when you start, they probably won't charge properly. I doubt you will damge them at C/10, but just get another charger. You can probably mooch one from a friend who has forsaken that technology.