RunRyder RC Helicopter Topic - NiMH battery gurus?

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Main Discussion > NiMH battery gurus?

mckrackin
Key Veteran
Location: lucasville,ohio USA

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Picked up a new toy at my LHS today.
I'm ordering a new 5000mAh 2S lipo but for now I have the battery the kid at the shop suggested.
A 3000mAh 7.2 volt NiMH.

What rate should I charge?
What is the max voltage per cell?

Thanks guys.

10-28-2009 02:18 AM

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Thumpernator
Senior Heliman
Location: Senoia, Georgia, USA

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My Triton Charger manual recommends 1.5 amps for a two hour charge and 3 amps for a one hour charge. It's better to charge at the lower amperage. It's less stressful, increases the lifespan, and tends to get closer to it's max charge.

This charger selects the proper voltage automatically, so I can't help ya with that part.

Dave
Crashing is not authorized.

10-28-2009 02:27 AM

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airboss
Elite Veteran
Location: OC ,california

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Nimh we used to charge them the fast way, using a car battery and some piano wire about 50 inches long (resistor) attach a volt meter to the battery side of plug and when volts start to decrease its done.
those batteries can be charged at unreal rates comparwed to a lipo, 10C is not uncommon.

OCRM....flyBlackstarr.org.

10-28-2009 02:28 AM

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bart2546
Heliman
Location: Canal Winchester, OH - USA

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I can tell you that the the pack should be charged at a max of 3 amps. I personally take it .2 to .4 amps less than the maximum. Just my personal preference including safety. However it's a give and take situation. If you charge it at 3 amps, you'll get a quicker charge and a better performing battery, but the OVERALL life of the battery will be shortened by forcing the charge in at such a quick rate. (Not the run time per charge, but how long the battery will last before it will not hold a charge)

The less amps you pump into it will cause the opposite. You'll have a better overall life of the battery but a slower charge time and you MAY get less performance out of it. But I will say that regarding the performance issue, I have never seen a difference myself.

NiMH do not get a memory NEARLY as easily as a NiCD however it can still happen so it's recommended that every so many charges you drop it down pretty low and then recharge.

Once nice thing about a NiMH is that when the charge starts to drop, it starts slowing things down, so instead of it running like a champ then BAM done, it'll get slower and sluggish as it's dying.

Regards, Brandon

10-28-2009 02:29 AM

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mckrackin
Key Veteran
Location: lucasville,ohio USA

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The charger got to 9.04 volts and started fluttering between 9.03 and 9.04.

I stopped it because I don't know what the finished charge voltage should be.

So it seems somewhere around 1.5 and 1.6 volts per cell.
Does that seem right?

10-28-2009 02:47 AM

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mckrackin
Key Veteran
Location: lucasville,ohio USA

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Quote
those batteries can be charged at unreal rates comparwed to a lipo, 10C is not uncommon.

10C would be awesome.That's like 6 minutes

10-28-2009 02:55 AM

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Helico-pteron
Senior Heliman
Location: Northeast Illinois

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Quote
Picked up a new toy at my LHS today. I'm ordering a new 5000mAh 2S lipo but for now I have the battery the kid at the shop suggested. A 3000mAh 7.2 volt NiMH. What rate should I charge? What is the max voltage per cell? Thanks guys.

Charge at 1C, which is 3A.

Discharged voltage per cell is 1.2V or 7.2V
Charged voltage is 1.4-1.5 per cell or 9V

Let your charger charge the battery. If you to take a moment to look at what what the voltage means in your last post, 9.04V/6=1.5V per cell. The charger was trickling in that last bit of capacity(mAh).

If your charger is a peak charger, set the mAh rating to 4000mAh. That way you know you will get a full charge.

If your charger works on cell count and cell type, set the 1C charge rate(3000mAh=3A, 4000mAh=4A, 5000mAh=5A, etc.)

If you are getting a lipo, my guess is you have a lipo charger, so you will select cell type(lipo), cell count(2) and charge rate(1C). The charger will do the rest.

1C is the rate equal to 1 x capacity. At 1C, regardless of capacity(mAh), the battery will take one hour to charge.

2C is twice the charge rate, so it will take 1/2 hour to charge.

For example, charging at 2C, your charge rate would be 6A.

All these examples are using your 3000mAh pack. Never charge NiMh packs more than 1C. Lipo batteries, depending on brand can be charged up to 5C.

I recommend no more than 2C if you are in a hurry. Under normal circumstances, charge everything at 1C.

Hope this helps.

Matt

Synergy HZ | Synergy SR

10-28-2009 03:02 AM

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jschenck
Elite Veteran
Location: La Vista, NE.

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Typical NiMH charge rate is 1C which means charge at the rate of what the pack is 1 times the capacity. Charge this pack at 3000mah.

How much does this battery weigh?

.. P-gas, T700, V50c/u, R50T, T4/250 and a Cricket ..

10-28-2009 03:05 AM

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beidle99
Senior Heliman
Location: West Deptford, NJ

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When I was racing electric cars/buggies/trucks it wasn't uncommon to charge at 5 amps on a 3300 mah nimh and peak before a race at 8 amps. And yes the 8 amp peck does deplete the packs life span, but generally that was only seen in the most competitive circles of stock racing. 2 of my 5 year old race packs are used for my heli/airplane starter and will last for weeks and start 90's with ease. your not going to hurt it by charging at 5 amps.

Who raised the ground since I took off?

10-28-2009 03:13 AM

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tukkus
Senior Heliman
Location: ma

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I'm going to go against the grain and say to charge it at a lower rate until you get more familiar with the battery.

All of my Nimh batteries have needed something along the lines of a 1/10C or they show a false peak and get hot which lowers the life of the battery.

I would recommend charging the battery at .3 Mah which should take about 10 hours.

Maybe your battery is a better quality than the ones I have but mine all seem to need a 1/10C or they get hot.

If you charge it at a 1C rate make sure you check to see if the battery gets hot and if it does then you need to lower the charge rate.

10-28-2009 03:13 AM

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Helico-pteron
Senior Heliman
Location: Northeast Illinois

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tukkus, what charger do you use?

If they don't get hot, they aren't fully charged. It's a good sign for them to be hot at the end of a charge.

Synergy HZ | Synergy SR

10-28-2009 03:17 AM

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jschenck
Elite Veteran
Location: La Vista, NE.

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I would disagree - if your pack is hot when you are done charging then you either over charged it or charged it too fast. That rule may work ok for power packs that are going into a car but for an RX pack on a heli you want reliability not peak charged performance. keep the pack cool and use a load bearing voltage meter before flying.

.. P-gas, T700, V50c/u, R50T, T4/250 and a Cricket ..

10-28-2009 03:21 AM

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Helico-pteron
Senior Heliman
Location: Northeast Illinois

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Quote
That rule may work ok for power packs that are going into a car but for an RX pack on a heli you want reliability not peak charged performance.

...and that is exactly what he is talking about, this is an RC Car pack, not an Rx pack.

Please don't confuse the two, you guys are beginning to merge all kinds of battery opinions in a one battery thread.

Besides, who still uses NiMh Rx packs?

Synergy HZ | Synergy SR

10-28-2009 03:26 AM

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mckrackin
Key Veteran
Location: lucasville,ohio USA

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Thanks all.
From the wide range of info,1C pops up most so I'll go with that.
I just didn't want to ruin this battery before my lipos come in the mail.

1.5 volts seems right too.
Next charge,I'll let the charger finish.I think it was wrapping up when I stopped it.

I even appreciate the advise on lipos even though I have lipo batteries out the wazu.lol....This my first NiMH battery pack.

Now on to the rear steering mod and maybe a BL upgrade.

It's a rock crawler by the way.
Had to keep that quiet til I learned something so the thread wouldn't get tossed off into the desert known as off topic or even worse,the battery forum where there is no mention anywhere of NiMH.lol...

Thanks again for the help.

10-28-2009 03:28 AM

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Ace Dude
Elite Veteran
Location: USA

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Well, the first few charges should be at C/10 for 14-16 hours.

Max voltage should be around 1.45v/cell.

10-28-2009 03:32 AM

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tukkus
Senior Heliman
Location: ma

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Helico..... if a pack is getting hot that isn't a measure of it being fully charged...it's just hot, which isn't good for the life of the battery.

A battery being charged at to high of a rate can get hot and that isn't a sign of being fully charged or even near it...it's a sign of the battery being damaged.

I use the Hobbico Elite charger for my lipos,NiMH and Nicads.

NiMH and Nicads are made with different materials depending on the maker so some might handle a higher charge than others but once they start getting hot from charging a different charge rate should be used.

10-28-2009 04:07 AM

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Ace Dude
Elite Veteran
Location: USA

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Heat is a sign of over-charging. They should never get hot while charging. NiMh will get slightly warm when fully charged.

The best way to charge NiMh is with a temperature sensor in your charger to prevent overcharging. Ever wonder why some chargers have a temperature sensor?

10-28-2009 04:19 AM

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kkuehnisr
Heliman
Location: braidwood,il,usa

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We used to charge 3300 at 5 amps also they get very warm almost hot but it does not hurt them. Do not tricle charge them

10-28-2009 09:02 AM

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BeltFedBrowning
Veteran
Location: Albany, MO USA

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I charge the 8 cell Nimh 3000mah battery on my Eco8 heli at 3 amps. I don't even have to take it out of the heli. It does get hot but I have been using this battery for years. It gets hot when I fly, it gets hot when I charge. I love not having to set a timer for the flight. I just fly till the headspeed gets too low to fly!

10-28-2009 02:51 PM

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pgoelz
Veteran
Location: Rochester MI

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Quote
Heat is a sign of over-charging. They should never get hot while charging. NiMh will get slightly warm when fully charged.

True.... and false.

Yes, heat is a sign of overcharging. But overcharging and heat are not always a bad thing. That is how "end of charge" is usually sensed in NiMh (and NiCd) cells. When the cell reaches 100% charged and the charge continues, the excess energy is dissipated as heat. The heat rise causes the cell voltage to decrease slightly while being charged at a constant current... this is the "peak" the charger looks for to determine when to discontinue the charge.

NiMh cells generate some heat while charging normally and more heat when they enter overcharge. They are designed to be able to tolerate some overcharge.

Unlike NiMh, NiCd cells actually COOL during charge and then warm when they enter overcharge.

A new NiCd or NiMh pack should be slow charged at between 1/20C and 1/10C for at least 16 hours before the first use. This is because in a new pack, the state of charge of the individual cells is unknown. If they are at different states of charge and peak at different times during a peak detecting fast charge, the charger may not be able to detect an overall pack voltage peak and either drive some cells too far into overcharge or worse, fail to terminate the charge at all. That will damage cells and make the pack VERY hot.

Paul

Paul Goelz
Rochester MI USA
http://www.pgoelz.com

10-28-2009 07:00 PM

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