nihm or lipo

[NWarty]

Jettas will try to destroy themselves anyways

And yes, I own a MkIV

[Shaggy39]

Loo, too true! Not the proudest moment in my car history (owning it OR blowing it up!). As you can imagine my mates have never let me forget it.

I remember going to the scene of fire after the car had been taken away and the only thing I found that had survived was one of the gold connection blades out of the deans connector!

[markbt73]

The first step for anyone should be to get a good charger that can handle different battery chemistries. I've found that using a decent charger can wake up old batteries, especially after a few cycles. I even have some old NiCds that I've revived using my new charger (Duratrax Onyx 245).

I use all 4 types of batteries. My biggest issue with lipo is that I'm not willing to modify an older chassis to fit a new battery, and even the "stick pack shaped" lipos often don't fit. So for the classics with stick-pack-shaped battery slots, I stick with NiMH.

But for the cars that can accommodate a modern lipo, a 2S with a good silver-can 540 is a great combination for bashing around.

[Tamiya Era]

Just a Quick Q about NiMh 7.2v Battery:

(can i use the 7.2v NiMh battery until it dies then fully charge it? or it will harm the battery life span? )

Thanks

[speedy_w_beans]

A great resource on batteries: http://batteryuniversity.com/learn/

[Tamiya Era]

A great resource on batteries: http://batteryuniversity.com/learn/

indeed, but i didnt get an answer to my Q from there..

[InsaneJim69]

Yes nimhs can be fully discharged with use then recharged. Will actually help keep the cells healthier.

Cant believe this thread is still open. Lol.

James

.

[speedy_w_beans]

indeed, but i didnt get an answer to my Q from there..

I think in the discharging section they talk about nickel-based chemistries delivering 95% of their capacity by the time the cell voltage hits 1.0V.

In practice most people fully discharge NiCd batteries to 0V to avoid memory effects. With NiMH batteries, though, I'm under the impression these cells don't like to go below 0.9V per cell. The LiFe cutoff voltage in most Tamiya ESCs (5.5V) is almost a perfect match for NiMHs (6 cells * 0.9V/cell = 5.4V).

[Mokei Kagaku]

I think in the discharging section they talk about nickel-based chemistries delivering 95% of their capacity by the time the cell voltage hits 1.0V.

If that's stated, it's either related to a specific (probably nominal) discharge current. Alternatively, it's a comfortable but not very accurate simplification of reality. This misconception is often based on the assumption that Ni-based battery chemistries have similar characteristics to lead-acid batteries, where the dilution of the electrolyte during discharge actually makes the voltage a pretty good indicator for the SOC (state of charge as a percentage of nominal capacity), but only when the voltage is measured with no load. For Ni-Cd and Ni-MH this is not the case, as the electrolyte is just a carrier and not an active part of the chemical process during discharge and charge and the density of the electrolyte thus stays virtually constant, keeping the internal resistance of the cell pretty constant too.

So, in reality the voltage at any SOC heavily depends on the discharge current (also for Lead-Acid when voltage is measured under load). Furthermore, the actual capacity depends on the load profile and isn't a fixed figure, so estimating SOC at any specific voltage and total available capacity for a load/load profile can only be done by referring to empirical data and simulations based on empirical data, something any serious battery manufacturer will of course offer for multiple different load profiles, instead of stating a fixed "universal" figure.

[speedy_w_beans]

I agree with the details you supplied.

Let's go back to Tamiya Era's question about discharging a NiMH pack until "it dies." Any concerns about individual cell polarity reversal and permanent damage? It seems like NiMH does suffer some damage when deeply discharged due to cells not necessarily being matched in a pack. Using a cutoff would help protect against this damage (but not guarantee it). I'm not reading about the same concerns, or same level of concern, with NiCd.

[twisted]

good enough as any place to talk about where you guys are getting lipos that fit in alot of the tamiyas. so far the best i have found is the peak performance 4200 45 c stick lipo.

im running a df03 and the battery compartment is tight.

[Tamiya Era]

So it is not advised to let the nimh battery to die at all. Right?

[speedy_w_beans]

Here's what I would do with NiMHs:

1) Use a good quality pack.

2) Use good connectors, like Deans plugs, to minimize voltage drop and heat at the connector itself.

3) Use the LiFe cutoff setting if you have a Tamiya TEU ESC to semi-protect against cell reversals in a stick pack. If you don't have a cutoff, just stop driving before the speed really drops off. Don't drive it until the model comes to a complete stop.

4) Store NiMHs fully charged.

5) Due to self-discharge, cycle stored packs once every 2-3 months if they're not being used regularly. It's better to have fewer packs and cycle them more frequently to keep them healthy.

The packs I used the most were still doing well after 3 years; the packs I stored a lot (and cycled every now and then) started dying one by one.

Enjoy!

[Tamiya Era]

Here's what I would do with NiMHs:

1) Use a good quality pack.

2) Use good connectors, like Deans plugs, to minimize voltage drop and heat at the connector itself.

3) Use the LiFe cutoff setting if you have a Tamiya TEU ESC to semi-protect against cell reversals in a stick pack. If you don't have a cutoff, just stop driving before the speed really drops off. Don't drive it until the model comes to a complete stop.

4) Store NiMHs fully charged.

5) Due to self-discharge, cycle stored packs once every 2-3 months if they're not being used regularly. It's better to have fewer packs and cycle them more frequently to keep them healthy.

The packs I used the most were still doing well after 3 years; the packs I stored a lot (and cycled every now and then) started dying one by one.

Enjoy!

Excellent mate!...I am doing same as ur steps except for the deans plugs..better to try them.:-)

I dont have a discharge, so it is fine discharging it via rc it self. Right?

Regards

[speedy_w_beans]

Excellent mate!...I am doing same as ur steps except for the deans plugs..better to try them.:-)

I dont have a discharge, so it is fine discharging it via rc it self. Right?

Regards

Sure, it's perfectly fine to discharge with the RC itself. I finally bought a charger with discharge capability so I could just (lazily) run a discharge/charge cycle without actually running a vehicle, yet keep the pack maintained.

[Tamiya Era]

Thank you so much buddy....

So I conclude that, of the pack is used regularly then the discharge should be every 4 months. And to keep it stored, must be charged with 50% or full to maintain the cells loose of power.

Right?

[speedy_w_beans]

Basically my recommendation is to discharge the pack once every 2-3 months either by actual driving or with a discharge function in a charger, then fully charge the pack and put it back on the shelf. NiMHs like to be stored with full charge, but they also have relatively high self-discharge, so you have to do something to maintain them. This is a basic approach to just preserving the investment. Hopefully we all drive cars and cycle packs more frequently! It's much more satisfying to drive with a freshly charged pack!

[Tamiya Era]

Much appreciated mate for such a clarification. .

What I do is:

After I charge the pack, I play with it little ( 5-10 min) then play again tomorrow and on day 3 the battery statrs to die, so I stip immediately and let it cool and charge it and keep it stored for next play.

This is how I treat the pack!..

[Boothy]

What does the discharge C rating mean on the lipo battery's?

I am looking at these two:-

http://www.modelsport.co.uk/core-rc-4000mahr-7.4v-20c-lipo/rc-car-products/366384

http://www.modelsport.co.uk/overlander-7.4v-30c-3250mah-lipo-sport-track-pack/rc-car-products/379011

The Overlander is slightly longer (2mm) but measuring my nimh looks like it should still fit anywhere an nimh will.

The Overlander is a tenner less but is only 3250 mAh vs 4000 mAh (I am guessing this means shorter run time?) However the Core has a discharge rating of 20C vs the Overlander's 30C with an 8 second bust discharge of 50C.

So I am guessing the higher discharge rate the better? Does that mean the Overlander would be quicker but not last as long?

[danb1974]

C rating multiplied by capacity tells you how much current the battery can deliver

4Ah * 20C = 80Amps

3.25Ah * 30C = 97.5Amps

But the motor is the one who pulls current, to pull 80amps (while slamming throttle from standstill, that is) you need a pretty beefy brushless system

[Boothy]

This lipo thing might be happening sooner rather than later.

I bought a team Orion rocket pack 5100 at Christmas from my LHS for about £45. As the weather has been pants here I have not had much chance to use it but tried it once about a week ago in my new built blitzer with super stock motor and tbh it was much slower than I expected and the run time was not great.

I re charged it after use as I hoped I may get chance to use it before now and once again today slow blitzer and probably 5 mins before the cut off kicked in. Grrr

It's back on charge now hoping I can get out before it goes dark, the only thing I can feel is that the two cells at the opposite end to the lead are much hotter than the two near the lead and the two middle are some where between, is that normal?

I never had these issues with my last mtronics 3700 I got a couple of years ago when I bought it, however that has been sat about so probably need a few cycles.

The only thing I don't have is a good charger, I just have a ripmax delta peak charger. So am I doing something wrong? I am guessing storing charged should not be an issue? Have I bought a duffer that needs to go back?

I know lipos tend to blow up but at least they work up to the point that they detonate your car

[SteveU30]

And that's why I hate NiMh, with LiPo you have way more information to tell you what's going on inside the battery.

What Amps are you charging your rocket pack at? Ideally you should be at 5A (5.1A would be even better) for around an hour (at which point your charger should switch over to trickle) in order to get the best out of it.

[Boothy]

And that's why I hate NiMh, with LiPo you have way more information to tell you what's going on inside the battery.

What Amps are you charging your rocket pack at? Ideally you should be at 5A (5.1A would be even better) for around an hour (at which point your charger should switch over to trickle) in order to get the best out of it.

It was at 3.5a as it says on the battery to charge at a max of 5a so I thought better to charge lower? However today to speed things up I did charge at 5a and I must say there was a huge difference when I took the car back out!

The thing was quick... much quicker than the first two uses and I got a good 20-30 mins run time, I am sure lipo would be better but at least the battery seems to be working now.

Out of interest do I need to leave them charged or discharged? I do not know what to do with the pack now as last time I charged it and then it was shot by today so do I need to charge before use?

Andy

[SteveU30]

 

It was at 3.5a as it says on the battery to charge at a max of 5a so I thought better to charge lower? However today to speed things up I did charge at 5a and I must say there was a huge difference when I took the car back out!

The thing was quick... much quicker than the first two uses and I got a good 20-30 mins run time, I am sure lipo would be better but at least the battery seems to be working now.

Out of interest do I need to leave them charged or discharged? I do not know what to do with the pack now as last time I charged it and then it was shot by today so do I need to charge before use?

 

Andy

Another issue with NiMh, they work best fresh from a charge (not literally as you should let the cells cool first) but they are also best stored fully charged as they will discharge over time (LiPo much less so, in fact LiPos shouldn't be stored fully charged but partially charged). This creates the dilemma of what to do with a NiMh that's been stored for say a month as it won't be fully charged, you shouldn't partially charge it and ideally it should be fully charged before use to get the best performance out of it!

Hence why I love LiPo so much (potential ticking time bomb issues aside).

[vrs55]

I run my battery down by setting my car up on a box and running it until battery is low then charge ready for taking out the next morning