Titanium MD-3000 battery cooker....I mean charger

[tre]

I asked 3 people at battery junction if the MD-3000 can be used to charge AA eneloops and 2 said it was ok and 1 said no. I found one thread here that said it may not be good for eneloops but most said it is ok. I decided to try my new MD-3000 to charge Eneloops.The charge current for AA, C, and D cells is around 1.6A. I know this is high but it is still 1C (for AA eneloops) which in theory is ok. The eneloops are about 3 months old with about 5 cycles on them. They stayed cool for the first 80% or so of the charge and then started warming up. Then I hear Hissss, Hissss, Hissss, (on and off at regular intervlas) coming from behind me:thinking:. I dont know if the noise was the charger or the emeloops but one of them did not sound happy. I felt the eneloops - OUCH - they were hot! I measured them over 130F with an infrared thermometer (and that was after three of the 4 already terminated the charge). They were too hot to hold for more than 1 or 2 seconds. They came off the charger at just over 1.4V so they did not get over charged. They were still all around 1.4V this morning.



The MD-3000 seems ok for my Tenergy NiMh 5000mah C Cells. They do get quite warm at the end of the charge though. I measured the C cells at 120F and just over 1.4V when the charge terminates (right on the border of too hot to hold). Does this seem normal? I feel like I am cooking the batteries.

 

[LEDAdd1ct]

I would like to know the answer to this as well:

Is 120 degrees F acceptable for a cell at the end of charge?

1.6 amps is below both 1.0C and 0.5C, so...?

This charger appeals because at 1.6 amp charge rate, it should make the negative delta V termination signal pronounced.

 

[lwknight]

Well, I tried one too. Its a piece of crap. It even fries D cells.
I posted this several times on this forum but can't seen to get the word out.

I think the charge rate is actually a time weighted rate. The pulse voltage is/must be too high.
I imagine that it actually charges at a much higher rate but the pwm averages it lower.
The more the cells near full charge the hotter they get and the more the pwm sounds off in musical notes.

I tried the same cells in a powerex 808m and it did not get the cells hot and they lasted twice as long in run time tests. I only charged eneloops in the md3000 1 time and they were not happy either.

 

[Mr Happy]

This sounds like an interesting question to follow up on. In my "hot battery" thread I have proposed that hot batteries are often the fault of the charger and not the charging current.

Perhaps when I have a moment I will do a test where I charge an AA eneloop at 1.6 A using an external power supply and measure the temperature during charging to see what happens under controlled circumstances.

 

[LEDAdd1ct]

I tried the same cells in a powerex 808m and it did not get the cells hot and they lasted twice as long in run time tests.

This makes things tougher in terms of buying a charger. On Amazon, there is more than one report of the 808M catching on fire or baking cells or just plain failing in interesting ways. No thank you.

Nearly every charger I've looked at either catches on fire, bakes the cells, or fails prematurely.

Google MH-C808M to read reports of it frying batteries and itself.

 

[Mr Happy]

This makes things tougher in terms of buying a charger. On Amazon, there is more than one report of the 808M catching on fire or baking cells or just plain failing in interesting ways. No thank you.

Yup, the gap between charger theory and well executed chargers you can actually buy is quite large. Even the mostly excellent C9000 has some significant design errors if you analyze it closely.

But in spite of my previous comment, if you want a trustworthy eight cell charger that won't catch fire, melt down, or cook cells, then get two MH-C9000's. The C9000 may have some technical mistakes in the way the firmware has been implemented, but the hardware is absolutely excellent quality. And if you should happen to get a dud unit, Maha customer support is excellent. If your unit has a manufacturing fault they will by all accounts put it right for you no questions asked.

 

[lwknight]

Well, after doing some research it seems that most anything electrical could catch fire for someone. The more that are on the market , the greater the chances of someone reporting that it gets hot or smokes. Maybe whatever you buy can have flukes so when you get a good one , cherish it.

The md3000 is the only charger that I ever used that made my batteries so hot that they wreaked fumes. So far my c808 is a very smooth champion. Also note that the reports on the c808 getting hot were 2 or more years old so maybe the problems have been fixed.

 

[Yamabushi]

Is 120 degrees F acceptable for a cell at the end of charge?

The Eneloop Handbook states "Nickel Metal Hydride batteries like eneloop sometimes get as hot as 50ºC (hot when touched), but it is not abnormal."

50°C = 122°F

 

[Mr Happy]

Is 120 degrees F acceptable for a cell at the end of charge?

That's an interesting question.

When NiMH batteries are being charged the supplied current is converted to chemical energy and stored inside the battery. However, when the battery is at the end of charge it no longer has any capacity to store the supplied current as energy. Instead, what happens is that the electrolyte is decomposed by electrolysis into hydrogen and oxygen gas which builds up pressure inside the cell. The cell is sealed to stop this gas escaping, but if the pressure is too much the safety seal will pop and the gas will get out. This is the hissing sound you sometimes hear when NiMH cells are overcharged. Hissing is bad.

Now, you may ask, what happens to this gas if it can't escape? The answer is that the cell contains a catalyst to convert the hydrogen and oxygen back to water. As long as the overcharging condition is not too extreme the gases get converted back to water, the pressure is reduced, and everything is OK. This is why you can charge an NiMH cell at a low rate like 0.1C for a long time without damaging it.

What about the temperature then? This is where it gets interesting. The rate of chemical reactions goes up when the temperature is increased, including the recombination reaction between hydrogen and oxygen inside an NiMH cell. If the cell is warmer, the recombination reaction can proceed faster, and the overpressure condition can be better controlled. So it is actually a good thing for a cell to get warm at the end of charging. It will reduce the risk of the safety seal popping and losing electrolyte.

As with many things, it is a balance. Too hot is bad, but too cold is bad too. Also, a hot cell may suffer from bad side reactions, so you don't want it to remain hot for too long. In an ideal world a cell will warm up at the end of charging, then charging will finish, the cell will cool down again, and everything will be good.

 

[LEDAdd1ct]

But in spite of my previous comment, if you want a trustworthy eight cell charger that won't catch fire, melt down, or cook cells, then get two MH-C9000's. The C9000 may have some technical mistakes in the way the firmware has been implemented, but the hardware is absolutely excellent quality. And if you should happen to get a dud unit, Maha customer support is excellent. If your unit has a manufacturing fault they will by all accounts put it right for you no questions asked.

I read over my previous comments, and I now realize I did not mention anywhere that I need a charger to accommodate three or four "C" cells. I would need some sort of holder for my four batteries, and connections to fit the slots. I just checked, and the PDF indicates it can charge up to two amps per cell. So the charge rate is okay for my "C" cells, but they won't fit.

Well, after doing some research it seems that most anything electrical could catch fire for someone. The more that are on the market , the greater the chances of someone reporting that it gets hot or smokes. Maybe whatever you buy can have flukes so when you get a good one , cherish it.

The md3000 is the only charger that I ever used that made my batteries so hot that they wreaked fumes. So far my c808 is a very smooth champion. Also note that the reports on the c808 getting hot were 2 or more years old so maybe the problems have been fixed.

Before posting about the dangers of the C808, I read the reviews and studied the time stamps. A review dated May 7, 2012 states:

"There is a third and a very seriously flaw with this charger. While recently charging up batteries for an event, I heard a loud "pop" coming from the charger and next, there was the smell of burning wires. I quickly unplugged the charger as it was too hot to handle. Evidently, the charger shorted out. A very dangerous situation, needless to say. I was very thankful the unit did not cause a fire! Stay away from this charger - even if this is the case of a "few bad apples" (which would indicate a quality control issue-a growing consumer concern, especially with imported products). Surely, this charger is not worth the risk of a hazardous fire. Because of these issues, I would give it *zero* stars if I could."

The Eneloop Handbook states "Nickel Metal Hydride batteries like eneloop sometimes get as hot as 50ºC (hot when touched), but it is not abnormal."

50°C = 122°F

Thank you for the quote!

As with many things, it is a balance. Too hot is bad, but too cold is bad too. Also, a hot cell may suffer from bad side reactions, so you don't want it to remain hot for too long. In an ideal world a cell will warm up at the end of charging, then charging will finish, the cell will cool down again, and everything will be good.

Your knowledge of electronics and electronics theory exceeds mine by a mile, but I always enjoy gleaning what I can from your posts. I understood this one for the most part, and I am grateful for it.

 

[Mr Happy]

I read over my previous comments, and I now realize I did not mention anywhere that I need a charger to accommodate three or four "C" cells. I would need some sort of holder for my four batteries, and connections to fit the slots. I just checked, and the PDF indicates it can charge up to two amps per cell. So the charge rate is okay for my "C" cells, but they won't fit.

I am sorry, I didn't think about C cells. I am too used to thinking about AA cells.

 

[VidPro]

""The rate of chemical reactions goes up when the temperature is increased, including the recombination reaction between hydrogen and oxygen inside an NiMH cell. If the cell is warmer, the recombination reaction can proceed faster, and the overpressure condition can be better controlled.""

How warm? I have never found this to be true in the situation of a hot battery. Most of the charts show that as temp goes up the pressure also goes up, at this end of charge area.

From http://www.sciencedirect.com/science/article/pii/S0378775312003886
""As the temperature increases, both reaction rates increase very rapidly, even though the solubilities of the gases in the KOH electrolyte decrease with temperature."" most of the rest of the page I cannot interpret, and i am not buying the paper for the whole story

From :http://www.google.com/imgres?imgurl...=75&tbnw=123&ei=HAsOUenTBOb5igKQu4GgAg&itbs=1
(Google attached link to refer to pressure temperature chart)
This chart style comes up often and shows that pressure is increasing rapidly when most of the battery is charged. the pressure is already getting high, before the temperature really goes way high.

""With either cell type, the drop in charge acceptance at higher temperatures
remains a significant concern to product designers who are mounting the cells in
close proximity to heat sources or in compartments with limited cooling or
ventilation. ""
Even though none of them will modify the rate at the end of charge to increase cell acceptance, and reduce heat and pressure, by going slower at that end.

and from http://i163.photobucket.com/albums/t299/Barrakketh/temp/partone-11.gif
similar chart which shows pressures at high rise, and both going quite crasy, After 100% charge. Different charts show this different ways, as we know a CC at high rate for nimh will show high temp and high pressure even before 100% charges, all depending on the methods they use. They can usually reduce the rate to continue to 100% charge, without so much pressure and temperature.

Course i only looks at da pictures how much pressure would be Bad, and how much temp would be bad, would have to be adjusted on the graph lines to determine when one of them is a bigger problem than the other? All i see is they go hand in hand mostly on high rate end of charge, and even low rate overcharge.

So while you could warm up a battery to increase a reaction rate, none of these chargers are doing that, instead they are raising pressure and temperature at what i think is the worst time to do so. The li-ion alogrythm shows that charging things could be done without much pressure, recombination or not.

 

[Mr Happy]

How warm? I have never found this to be true in the situation of a hot battery. Most of the charts show that as temp goes up the pressure also goes up, at this end of charge area.

Oh, the pressure inside the cell definitely goes up a lot when it gets warm at the end of charge. The cell is designed for this and is sealed to keep the pressure in. When I say the high pressure condition can be better controlled, I mean the difference between high pressure that stays within design limits, and high pressure that gets so high that the cell vents with a hissing sound. You never want to hear that hissing sound when a battery is being charged. It represents an irreversible loss of capacity and performance.

 

[VidPro]

(amazon 808 review) I heard a loud "pop" coming from the charger and next, there was the smell of burning wires. I quickly unplugged the charger as it was too hot to handle. Evidently, the charger shorted out. ."
.

I bought my 808 late in time (try to get best revision).
I have caught my 808 style charger trying to blow up an AAA cell that was crap. of course I did not know it was crap. It was cooking it severly. But that cell has a release valve.
I have some old china cells with no emergency release valve. If i cooked them on it, AND they managed to build up pressure continually, they would take the charger out when they blew.

Normally the 808 has been very very good, terminating even some of the worse cells, and usually is terminating before a 100% charge. And i always am using the soft charge option (cept for the Ds). But my AAAs are all over the place, and much less predictable.