Maha Charger and multiple naked Li-Ions

[lemlux]

I just received my Maha C777 Plus II. Maha claims that the charger is capable of charging up to 4 Naked Li-Ions in serial or up to 12 NiMH or NiCad cells in serial.

I asked tech support whether it was safe to charge multiple unprotected Li-Ions in serial or in parallel or both.

Maha Tech Support advised that parallel was a bad idea because the cells would not equalize and that the cell with the lowest internal resistance would most likely overcharge.

Maha Tech Support also advised that the charger would register a completed charge as soon as any one cell in the serial chain was fully charged.

That cell would have to be removed from the serial chain to continue charging. It would make the most sense to complete the charge on each cell separately at this point. As expected, M T/S cautioned that it is adviseable to charge only near identical cells with similar charge levels in a serial string.

I don't know if I am comfortable with the assertion that charging would stop when any cell was fully charged. Is anyone knowledgeable prepared to comment?

 

[LitFuse]

Although I don't consider myself knowledgable on the subject, I think charging more than one cell at a time is a bad idea. At the least, I don't think you'll get the most out of them. At the worst, it could be potentially dangerous.


Peter

 

[highlandsun]

I'd follow their advice, but I don't understand the issue with parallel charging. I've charged up to 4 AA LiIons in series with some Radio Shack AA holders, but of course they were identical cells at very nearly identical state of charge to begin with. I've also charged 2-3 in parallel once or twice. Of course it makes sense that you get the most accurate voltage/current sensing by doing one cell at a time.

 

[mattheww50]

I'd rate the answer as maybe... The C77 Plus II is a strange beast. It puts a small surface charge on the bats to have a good idea how many live cells there are. What most are probably unaware of is the thermal sensor that you attach to the battery pack being charged (it is magnetic), or in this case, one of the cells. If that is cell that is fully charged first, yes the charging will shut down. What The C777 Plus II looks for is two things. A terminal voltage that is about right for the number of cells and room temperature, and for a sudden increase in the cell temperature. Most rechargeable convert charge to heat instead of chemistry once they are fully charged, so that's where the thermal sensor comes in.

I haven't used mine much on Li-ion cells, but I have certainly used it on NiCd and NiMh, and that's how it works.
However NiMh and NiCd are a lot more forgiving of overchargig then are Lithium Ion cells.

 

[highlandsun]

LiIon cell temp doesn't change during normal charging. By the time there is any temperature rise, the cell has already been destroyed.

 

[lemlux]

Sounds like we all share the same scepticism about the Maha tech support advice.

One at a time, these cells will be considerably more inconvenient to recharge than the protected cells in the Pila charger. It certainly makes it useful to have a number of recharged spares.

 

[LitFuse]

Lemlux, I thought long and hard about getting a C777 Plus II, in the end I've decided not to. I also could have picked one up for around $70 (5% previous order coupon plus a small credit for returned merchandise). There are a couple of reasons I decided not to get this charger.

1. I called MAHA customer service to inquire about any new models in the near future. They said that the replacement for the 777 Plus II will offer variable charging current, most likely 500mA, 1000mA, and 2000mA. The current unit is 800mA and this just doesn't seem to be optimal any more with the new higher capacity cells, especially the new 12,000 mA "D" cells. They didn't know/want to give a date when it would be available, but the CSR did say "three to six months". I have no idea if there is any actual truth to this statement.

2. I too was initially interested in this charger for charging bare Li-ions. I figured I could justify the cost because it would be good for other types of batts. as well. It certainly is a versatile charger, but I don't think it's optimal for either type. I think the Lenmar MSC1L is the ticket for the Li-ions. According to posts here at CPF it will charge a 1500 mAh cell in less than an hour, and is fully automatic. Contrast this with the 777's 400 mA charge rate for Li-ions and you can see that the Lenmar is going to be alot more convenient to use.

When the the new MAHA comes out, I will probably pick one up. In the meantime, I'm going to order the Lenmar Mach One for the lithium cells that I have on the way.

I should probably add that I have no actual experience with either of these chargers, nor do I consider myself particularly knowledgeable about batteries or battery charging in general. My opinions and decisions on what to buy are based on things I've read here and elsewhere. I think most of it is accurate, but I don't offer it as fact. I am a little intrigued/concerned about how the Lenmar can charge a 1500 mAh battery in less than an hour without damage. If we have any battery gurus here I would like to hear any opinions. Thanks.


Peter

 

[lemlux]

Litfuse:

I bought the Maha rather than the Lenmar only because I have some 10 cell and 12 cell packs that are beyond the capablities of my other chargers.

Also, when I looked at the Lenmar Mach One I noticed that it had replaceable "plates" for various cameras and camcorders. I didn't get the impression that a "plate" was available to fit the naked cylindrical Li-Ions. Can you direct me to the fixture that would hold 14500's, 17670's, 18500's and 18650's? I know how to make fixtures to which I can hook up alligator clips for the Maha, but I don't know what to do with the Lenmar.

Interesting input on the features of unreleased Maha products.

 

[LitFuse]

[ QUOTE ]
lemlux said:
Also, when I looked at the Lenmar Mach One I noticed that it had replaceable "plates" for various cameras and camcorders. I didn't get the impression that a "plate" was available to fit the naked cylindrical Li-Ions. Can you direct me to the fixture that would hold 14500's, 17670's, 18500's and 18650's? I know how to make fixtures to which I can hook up alligator clips for the Maha, but I don't know what to do with the Lenmar.

[/ QUOTE ]

lemlux, You will need to "homebrew" the interface between the Lenmar and the naked cells. I haven't done this as I haven't received my cells or charger yet. However, Ben H has this combination up and running as detailed in this thread. I think with a little pestering /ubbthreads/images/graemlins/poke2.gif we may even be able to get him to post some pics. /ubbthreads/images/graemlins/smile.gif


Peter

 

[lemlux]

Litfuse:

Thanks for the link. I had stopped following up on that thread.

I gather from Ben's comments that he soldered wires to one of the removable battery plates. If I had a charger, I would probably solder the empty end of leads with alligator clips to the donor battery plate.

 

[LitFuse]

I just ordered my Lenmar MSC-1L charger here. $51.97 shipped.

Peter

 

[lemlux]

I just learned something about the Maha charger that previously escaped me.

The Magnetic plate on the top surface is powerful enough to cause the alligator clip connector to stick to the positive button of (at least) my 37 mm long Powerstream 1/2 D Nicads. If I place the negative end of a 1/2 D cell against the moveable pins of the battery holder I can charge either one 1/2 D cell or two 1/2 D cells lined up serially by magnetically connecting the alligator clip and ignoring mechanical clipping.

Previously, it had been awkward to charge 1/2 D's fewer than 5 at a time in a 3D cell fixture.

My single cell chargers don't want to deal with a cell shorter than 43 mm long.

 

[Ben H]

Hi guys,

Pics of my setup are coming. I was gone all weekend and tonight I've got a hot date with my wife. /ubbthreads/images/graemlins/grin.gif Hopefully I'll get the pics posted tomorrow.

 

[LitFuse]

/ubbthreads/images/graemlins/popcorn.gif

 

[lemlux]

Several days after I received the verbal advice from Maha TS they finally responded to the same question I emailed to them prior to phoning.

The email hedged by saying that charging multiple units was fine with protected cells.

I'm going to play it safe and charge one at a time.

 

[Ben H]

Well, I've got the pictures, but right now imagestation is not letting me upload them so that I can post the pics of my charger set up. Stay tuned I'll try again later.

 

[LitFuse]

Looking forward to the pics Ben.

Peter

 

[snakebite]

warning!!!!!!! most camcorder type li-ion chargers depend on the stuff in the pack to terminate charging.bare cells on the lenmar is a bad idea.
the maha c777+2 is safe for bare cells and paralell groups.
many notebook packs have 3 or 4 cells in paralell and several of these groups in series.i would not try unprotected cells in series.

 

[Ben H]

I got the pics up on a new thread.
17670 Li-Ion cells & Lenmar MSC1L Charger

Lenmar said the MSC1L handles all the charging and does not rely on the protection circuitry of the cell. Here's what they said in response to me asking about this, "All of the charge controls are in the charger unit. The board inside the battery pack is for protection, not charge regulation."
I've used the charger about 8 times with no problems at all.