Charging just one Eneloop

I'm sorry if this has been addressed, but my searches on dummy batteries just give me in-use dummy cell threads.

I have several 4 bay, 2 channel battery chargers (the bundled Eneloop charger and the Maha MH-C204W). Can I put a dummy cell - I'm thinking a metal bolt - in one of the empty bays in order to charge a single cell? The Maha is charging at 2a. How would the charger sense a lone cell and terminate the charge appropriately?

FYI, this is for my partner; I have a big C-808 for my own batteries (since I'm a nerd and all...)

Firecop said:

I have several 4 bay, 2 channel battery chargers (the bundled Eneloop charger and the Maha MH-C204W). Can I put a dummy cell - I'm thinking a metal bolt - in one of the empty bays in order to charge a single cell?

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Almost certainly you can't. The charger is designed for the voltage of two batteries in that charging channel. If you try to charge a single battery it won't see the right voltage. At best it will refuse to charge, at worst it will damage the charger. I do not recommend attempting to do this, it could end in tears.

Mr Happy said:

Almost certainly you can't. The charger is designed for the voltage of two batteries in that charging channel. If you try to charge a single battery it won't see the right voltage. At best it will refuse to charge, at worst it will damage the charger. I do not recommend attempting to do this, it could end in tears.

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Tears till he replaces it with a seperate channel charger. :devil:
G27

Sanyo makes a USB charger for the eneloops that can do one or two batteries at a time. You can get them on Amazon.com for $14.99 including two AA batteries.

Good to know! Thanks for the info.

What about throwing in a fully charged battery with the dead one? Will the charged one just shunt the charge to the other, or will it get over-charged and be damaged?

He's cheap and wants to avoid spending more money than necessary. What a wuss!

Firecop said:

Good to know! Thanks for the info.

What about throwing in a fully charged battery with the dead one? Will the charged one just shunt the charge to the other, or will it get over-charged and be damaged?

He's cheap and wants to avoid spending more money than necessary. What a wuss!

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Good question, I'm eager to hear this answer!

On a paired channel charger you are meant to charge two batteries of the same kind and same state of discharge. You can't mix a fully charged battery with an empty one as that will confuse the charger and overcharge the full battery.

The thing to do with a two channel charger is wait until you have two empty cells to charge and then charge both at the same time.

I have a USB Energizer charger that does a fine job at doing just one Eneloop. Kinda cheap too.

Mr Happy said:

Almost certainly you can't. The charger is designed for the voltage of two batteries in that charging channel. If you try to charge a single battery it won't see the right voltage. At best it will refuse to charge, at worst it will damage the charger. I do not recommend attempting to do this, it could end in tears.

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Presuming two cells are required to complete the charging circuit, doesn't that mean they would be charging in a series formation?

And if they are charging in a series formation, then shouldn't the expected voltage remain the same for one or two cells?

And if the expected voltage remains the same for one or two cells, then the dummy cell concept should work, shouldn't it?

Bones said:

Presuming two cells are required to complete the charging circuit, doesn't that mean they would be charging in a series formation?

And if they are charging in a series formation, then shouldn't the expected voltage remain the same for one or two cells?

And if the expected voltage remains the same for one or two cells, then the dummy cell concept should work, shouldn't it?

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It might work, but it most likely will not. I would not try it due to the risk of damage to the charger.

When cells are connected in series the current is the same through each but the voltages are added. So with one cell plus a dummy the charger will see ~1.2 V, but with two cells present the charger will see ~2.4 V. That difference is large enough that it might be outside the circuit design parameters.

Mr Happy said:

It might work, but it most likely will not. I would not try it due to the risk of damage to the charger.

When cells are connected in series the current is the same through each but the voltages are added. So with one cell plus a dummy the charger will see ~1.2 V, but with two cells present the charger will see ~2.4 V. That difference is large enough that it might be outside the circuit design parameters.

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Yes, of course the voltage would be halved with only one cell.

Thank you.

Why would anyone design a charger as two, series, 2.4 volt channels (or 2.8 volt) and not two, parallel, 1.2 volt channels (or 1.4 volt)?

I've seen 2/4 cell chargers. I need to check the instructions, I thought you could use a specific bay or two to charge single cells.

divine said:

Why would anyone design a charger as two, series, 2.4 volt channels (or 2.8 volt) and not two, parallel, 1.2 volt channels (or 1.4 volt)?

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It's the difference between two channels in the charger and four channels in the charger. Designing for two channels obviously gives a potential cost saving over four channels. (You cannot charge NiMH cells in parallel, if that is what you are asking?)

I've seen 2/4 cell chargers. I need to check the instructions, I thought you could use a specific bay or two to charge single cells.

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It depends on the charger. Some can, some can't.

Mr Happy said:

...
(You cannot charge NiMH cells in parallel, if that is what you are asking?)
...

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In another thread, it was speculated that an NiMH charger which utilized two output rates was charging in parallel, and this is what caused a step-down in output when a second cell was added to the same charging bank.

Obviously, this can't be the case if you cannot charge NiMH cells in parallel, but I was curious as to why not. It seemed at least somewhat logical to me that if you can discharge in parallel, you should also be able to charge in parallel.

Anyway, I found this this quote in rcgroups.com which seems to explain Mr Happy's point quite succinctly:

A very very very bad idea! Never charge ni-mh in parallel! This is because of the voltage drop after a ni-mh has peaked, thus once the charger misses the peak detection, the voltage of the fully charged pack will start dropping, and when that happens the current will be shunted TOWARDS the fully charged pack. And since the voltage drops further with more overcharging, you will be prone to a runaway situation, and bad things will occur...

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I just learned yesterday that this voltage drop also raises havoc with series charging NiMH cells pursuant to SilverFox's explanation in post 9 of his thread on the Sanyo NC-MQN06 charger.

Hence, the preference for fully independent channel NiMH chargers.

Mr Happy said:

. (You cannot charge NiMH cells in parallel, if that is what you are asking?)

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I've been charging NiMH cells in parallel for many years. The old CCrane (Saitek) charger does it and does a very nice job, I might add. You do have to use matched cells. You don't want to connect two cells in parallel if their voltages are very different.

The CCrane is a very smart charger. It determines the capacity of whatever it's charging and picks a strategy to suit.

Hello Eluminator,

The Saitek charger is very interesting.

If I am remembering correctly, it only uses parallel charging for the bulk portion of the charge.

This is a lot different from hooking a couple of cells in parallel and charging them up.

The Saitek charger starts with a discharge, but you can by pass that. It then goes to a soft charge. Since it uses a discharge spike during charging, it can measure the loaded voltage of each cell and I believe it individually charges during the soft charge stage. Once the cells are "balanced," it changes to a parallel bulk charge where it charges full out until the cell temperature rises. It then, once again, enters soft charge mode until the charge is completed. The final balance is done during the trickle charge after the charge has completed.

This is almost as good as independent channel charging...

Tom

You guys have me sold. I'm going to get a voltage reader from batteryjunction and then pick up the USB charger from amazon. My question is, are ALL the USB chargers capable of charging one battery at a time? I'd hate to get it and then read the instructions telling me to only charge in pairs. :thinking:

jblackwood said:

You guys have me sold. I'm going to get a voltage reader from batteryjunction and then pick up the USB charger from amazon. My question is, are ALL the USB chargers capable of charging one battery at a time? I'd hate to get it and then read the instructions telling me to only charge in pairs. :thinking:

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I was going to suggest the Energizer Duo, but then I read that it indeed can only charge batteries in pairs. Can anyone confirm?

Or is the TPEC-TP1HR at batteryjunction a safer bet? I feally just want to extend the life of my batteries and I have so many single cell AA lights that I want to get a single channel charger that is safe to use/best with Eneloops.
:thumbsupr:thumbsdow?

I once read somewhere these fast chargers are never a good idea. I'd rather go for a slower charge if it'll extend the life of the cell.

I have the Energizer Duo and it does charge in pairs only