Nimh battery charging

[Caleb90]

Never charged nimh batterys. Charging at the same c rating you would for. Lipo depending on the mah rating. What does the av detection mean? Cells? The batteries are 7.2volt

Also what should the end voltage be?

 

[tntpoof]

your av is delta peak. that's the over voltage the charger will stop at.by adjusting that higher you can get a few more seconds out of a battery I dont charge my nimh at 1c doing so will limit there life span. I condition my ni at lowest charge my charger can do then bring that C rate up to .75 amps max.I always set cell count.

 

[Caleb90]

Any thing else i should know?

 

[Greywolf74]

Any thing else i should know?

"NiCad and NiMH batteries are amongst the hardest batteries to charge accurately. Whereas with lithium ion and lead acid batteries you can control overcharge by just setting a maximum charge voltage, the nickel based batteries don't have a "float charge" voltage. So the charging is based on forcing current through the battery. The voltage to do this is not fixed in stone like it is for the other batteries.

The coulometric charging efficiency of nickel metal hydride batteries is typically 66%, meaning that you must put 150 amp hours into the battery for every 100 amp hours you get out. The faster you charge the worse this gets. The minus delta V bump that is indicative of end-of-charge is much less pronounced in NiMH than NiCad, and it is very temperature dependent. (minus delta V is the setting on your charger you were asking about) To make matters worse, new NiMH batteries can exhibit bumps in the curve early in the cycle, particularly when cold. Also, NiMH are sensitive to damage on overcharge when the charge rate is over C/10. Since the delta V bump is not always easy to see, slight overcharge is probable. For this reason PowerStream does not recommend using simple minus delta V as a termination criterion for nickel metal hydride batteries.

However, modern algorithms have been developed to enable accurate charging without using a thermistor. These chargers are similar to the -delta V chargers, but have special measurement techniques to detect a full charge, usually involving some kind of pulse cycle where the voltage is measured during the pulse and between pulses. For multicell packs, if the cells are not all at the same state of charge, and if they are not balanced in capacity, the cells may fill up one at a time, blurring out the end-of-charge signal. In order to balance the cells it may take several charge-discharge cycles. Luckily, NiMH does not mind being overcharged at C/10 or less, which allows the charger to balance the cells during the trickle charge.
As the battery reaches end-of-charge oxygen starts to form at the electrodes, and be recombined at the catalyst. This new chemical reaction creates heat, which can be easily measured with a thermistor. This is the safest way to detect end-of-charge during a fast charge."

 

[Caleb90]

Come on now batman. Eennngggrish peeessss

 

[Greywolf74]

Come on now batman. Eennngggrish peeessss

The bottom line is the minus delta V setting is fine at 7mV. Dont charge a NiMH at more than 1/10C.

 

[Caleb90]

The bottom line is the minus delta V setting is fine at 7mV. Dont charge a NiMH at more than 1/10C.

1/10th c? A 3600 mah battery would put me at like .3amps

 

[Greywolf74]

1/10th c? A 3600 mah battery would put me at like .3amps

If you want to make it last as long as possible. You can charge it higher than that it will just shorten the lifespan and the capacity. If you do charge it faster then make sure you're using a temp sensor

 

[RustyUs]

Just looking at some of my manuals, and I'm really surprised there is no NiMh suggestion on charging practices.

Edit:
One manual stated...
NiCD/NiMH Auto Charge Mode:
In this mode, the charger automatically detects the connected NiMH or NiCD
battery and determines the proper full charge and cutoff thresholds. Setting the
upper charge current limit for safe levels based on your battery specifications
will ensure safe charging of your specific battery. If you are unsure of the
maximum allowable charge rates, set the charger to a maximum of 1C (battery
mAh/1000, i.e., 2500mAh = 2.5A).

Slower is better though. I don't miss carrying around a boatload of packs when heading to track practice/race.

 

[Greywolf74]

Just looking at some of my manuals, and I'm really surprised there is no NiMh suggestion on charging practices.

Edit:
One manual stated...
NiCD/NiMH Auto Charge Mode:
In this mode, the charger automatically detects the connected NiMH or NiCD
battery and determines the proper full charge and cutoff thresholds. Setting the
upper charge current limit for safe levels based on your battery specifications
will ensure safe charging of your specific battery. If you are unsure of the
maximum allowable charge rates, set the charger to a maximum of 1C (battery
mAh/1000, i.e., 2500mAh = 2.5A).

Slower is better though. I don't miss carrying around a boatload of packs when heading to track practice/race.

You can charge them at 1C but they wont take the max amount of mAh and they will heat up which is bad for the cells. I usually charge big stick packs and receiver packs at .5-.7A depending on how big the pack is and AA/AAAs I charge at .3A for 4 cells and .2A for 1 or 2 cells. Takes all night but they will get the full charge because it minimizes the coulometric charging efficiency problem.

 

[Caleb90]

These are for my boys granite mega that i got him for christmas. I will see how they work. Got them so the brushed motor would last longer and so it would help keep speeds down

 

[Greywolf74]

I really dont understand why NiMH has become the go to nickle pack for brushed RCs in the industry. NiCD are actually much better suited to that purpose and last longer than NiMH.

 

[Caleb90]

Never heard of em

 

[Greywolf74]

NiCD used to be the main go to for RC batteries. They can handle higher amp draws than NiMH which is why they used top be the main go to cells for power tools also. NiCD takes a little more care to keep them in good condition which I think is why NiMH has kind of taken over as the industry standard for nickle based packs.

 

[tudordewolf]

I really dont understand why NiMH has become the go to nickle pack for brushed RCs in the industry. NiCD are actually much better suited to that purpose and last longer than NiMH.

I think it's a variety of factors, capacity probably being the biggest one. Sub-c nimhs can go up to 5000mah, NiCads top out around 2400. That's not just double the runtime per battery, that's halving the weight you need to carry for an hour's bashing. Those are the extremes, most nimhs are closer to 3000mah, but most NiCads are 1800.

It's an interesting conversation to have, especially in the shadow of lipos and brushless dominating the bashing scene. I get the impression that nickel chemistry is largely run for nostalgia or safety reasons; I myself put together a brushless/nimh RC truck for my brother this Christmas to idiot-proof the battery logistics. Stick packs aren't obsolete yet, it's kind of fun to know they've been a format for 40+ years and are still going strong as the baseline.

The difference in current-draw capability doesn't emerge until you get into niche levels of tuning and low-turn-count motors, at which point the user is probably more aware of their battery choices and can select accordingly, going with nicad if they want the old-school vibe.

There's also the memory effect, which is still a source of controversy: regarding its existence, underlying mechanism, or even the origin of the theory. There's 4 paragraphs going back and forth about it on Wikipedia, with 3 "citation needed" and a few editors disagreeing about the subject.

There's the environmental aspect of  cadmium - NiCads have been banned in the EU except for replacements and for medical devices (which hints at its reliability); that kind of regulation can reach beyond borders when a multinational is developing a product
for multiple markets.

I still see NiCads used in outdoor solar lights, where their tolerance of subzero temperatures beats every other chemistry.

They're also still used in large commercial jets (probably military too) - I think the 787 Dreamliner was one of the first planes to use lithium batteries, and it had teething issues with battery fires.

 

[Bogda89]

Nimh can be charged very fast but only to let's say 50%. As it gets charged towards the end it will start to heat up. If goal is to charge to 100% 1/10 c is recommended. Charging at 1c until fully charged will produce a lot of heat towards the end.

I have been blasting some packs with 4c and over, but only from 0 to 50% of charge.

 

[Greywolf74]

I think it's a variety of factors, capacity probably being the biggest one. Sub-c nimhs can go up to 5000mah, NiCads top out around 2400. That's not just double the runtime per battery, that's halving the weight you need to carry for an hour's bashing. Those are the extremes, most nimhs are closer to 3000mah, but most NiCads are 1800.

It's an interesting conversation to have, especially in the shadow of lipos and brushless dominating the bashing scene. I get the impression that nickel chemistry is largely run for nostalgia or safety reasons; I myself put together a brushless/nimh RC truck for my brother this Christmas to idiot-proof the battery logistics. Stick packs aren't obsolete yet, it's kind of fun to know they've been a format for 40+ years and are still going strong as the baseline.

The difference in current-draw capability doesn't emerge until you get into niche levels of tuning and low-turn-count motors, at which point the user is probably more aware of their battery choices and can select accordingly, going with nicad if they want the old-school vibe.

There's also the memory effect, which is still a source of controversy: regarding its existence, underlying mechanism, or even the origin of the theory. There's 4 paragraphs going back and forth about it on Wikipedia, with 3 "citation needed" and a few editors disagreeing about the subject.

There's the environmental aspect of  cadmium - NiCads have been banned in the EU except for replacements and for medical devices (which hints at its reliability); that kind of regulation can reach beyond borders when a multinational is developing a product
for multiple markets.

I still see NiCads used in outdoor solar lights, where their tolerance of subzero temperatures beats every other chemistry.

They're also still used in large commercial jets (probably military too) - I think the 787 Dreamliner was one of the first planes to use lithium batteries, and it had teething issues with battery fires.

These are some very interesting points. I didnt even stop to consider the capacity factor or the environmental factor either.

One small disagreement I have is about the higher current tolerance only being a factor for niche levels of tuning etc. The higher current tolerance will make the pack run cooler in comparison to a NiMH pack and therefore last longer. That being said the capacity trade off probably isnt worth it. Thanks for the interesting read.

 

[pug]

NiCD used to be the main go to for RC batteries. They can handle higher amp draws than NiMH which is why they used top be the main go to cells for power tools also. NiCD takes a little more care to keep them in good condition which I think is why NiMH has kind of taken over as the industry standard for nickle based packs.

So I'm not crazy for wanting to use NiCds instead of NiMHs?

 

[RustyUs]

Never heard of em

Be glad. We had no other choice back in the day. 1400mAh were a BIG deal... stepping up from 1200mAh packs.

 

[Greywolf74]

So I'm not crazy for wanting to use NiCds instead of NiMHs?

Nope but NiMH packs are going to have more mAh.