NiCd/NiMh battery weight comparison

[mud4fun 1696]

I'm sure this must have been done many time before but not recently as far as I could see after a quick search.

I was curious as the difference in weights between all my various stick packs because even two supposedly same voltage packs seem to feel different weights just in the hand. Anyway here are the weights of my different types (I do have four each of most of these) but this covers a good range:

• Tamiya NiCd 1400mah, 7.2v = 326g
• Overlander NiMh 3300mah, 7.2v = 335g
• Absima NiMh 3600, 7.2v = 354g
• Sanyo NiCd 2000mah, 7.2v = 356g
• Sanyo NiCd 2000mah, 8.4v = 410g
• Sanyo NiCd 2000mah, 9.6v = 467g

What surprised me was the fact the Absima with a claimed capacity almost double the Sanyo for the same 7.2v weighs less. I was expecting it to weight more.

Also worth noting that although the Sanyo 8.4v pack weighs 54g more than its 7.2v sibling, my terra scorcher goes 4mph faster using the heavier 8.4v instead of 7.2v in conjunction with a Dyna Run Super Touring, why I have no idea as I thought top speed was limited by pinion sizing and motor rpm's not voltage?

I thought it may be of interest to somebody to know some of the charging history and retained capacity of these packs, some of which are 20 years old:

(Retained capacity is that stated by my Pro Peak Super Nova charger after each pack was fully discharged first, all taken over the last few days.

I have also confirmed these capacities on a SkyRc T100 which gives almost identical results.

All my packs are fully discharged and then charged before being put into storage (in a fireproof case) after use and have been since they were new.

The first charge is always a trickle charge at 0.4A, subsequent charges have all been fast charges upto a maximum of 3A

• Tamiya NiCd 1400mah, 7.2v = 20 yrs old, 1000+ charges, 1350mah (lost 50mah)
• Overlander NiMh 3300mah, 7.2v = 1 month old, 6 charges, 3000mah (lost 300mah)
• Absima NiMh 3600, 7.2v = brand new, 1 trickle + 1 discharge/recharge cycle, 3300 (lost 300mah)
• Sanyo NiCd 2000mah, 7.2v = 18 yrs old, 1000+ charges, 1800mah (lost 200mah)
• Sanyo NiCd 2000mah, 8.4v = 18 yrs old, 2000+ charges, 1600mah (lost 400mah) - my most heavily used packs, always used in with 13T Dyna Run Super Touring or Reedy 19T spec motors.
• Sanyo NiCd 2000mah, 9.6v = 18 yrs old, 100+ charges, 2000mah (no loss)

So in summary, Tamiya and Sanyo NiCd's that are over 18+ years old are still retaining most of their original capacity whereas brand new NiMh packs are not even taking 90% of their claimed capacity. Has anybody else experienced this sort of performance?

I will be switching to LiPo next year and gradually swapping all our fleet into them and I will be interested to know if anybody had done similar comparisons on a range of LiPos?

[sosidge 624]

Well, the 8.4v is faster because of the higher voltage.

I'm surprised you've got such a good life out of your NiCd, very impressive, you must be doing something right with them. Normally they will lose performance over time. Did you compare the average voltage under discharge?

The NiMHs are much more temperamental than the NiCds, so I'm not surprised the capacity is below the rating. They don't like a deep discharge, they should be cut off at 0.9V per cell. But basically I would have zero expectations from a cheap NiMH pack.

[wolfdogstinkus 1893]

I recently weighed 8x AA batteries from the quick drive thunder dragon. 

There wasn't much difference in weight to a small 3s lipo but obviously the lipo has more power and longer run time..

[Juictetin 10]

Really interesting, thanks for posting. That Sanyo 9.6v, no loss after 18 years !  

[mud4fun 1696]

55 minutes ago, sosidge said:

Well, the 8.4v is faster because of the higher voltage.

 

But how? I have always assumed (and obviously experienced) the fact that higher voltage generate substantially more torque, lots of twisted dogbones testify to that, however does this mean the motor has a higher number of rpm's on higher voltage? If not then how can the buggies top speed (confirmed by numerous GPS tests) increase so significantly with more voltage despite same gearing and a supposed max motor revs?

I can only guess that max motor revs is stated based on 7.2v but varies with voltage then? 

OR the buggy generates an amount of rolling resistance that limits speeds that is overcome by the increase in torque on 8.4v?

I'm certainly no expert on how electric motors work, I am just quoting personal experience and my confusion LOL

[Frog Jumper 3657]

There’s a lot of electrical engineering involved with big brain math with Greek letters and stuff, but at the end, it’s just a fancy way to say more voltage means more RPMs...

Terry

 

[Frog Jumper 3657]

To your comments about nicd vs nimh in terms of capacity and age, nicd has a long shelf life but not a long run time. Nimh is opposite. Read here, about halfway down..,

https://batteryuniversity.com/learn/archive/whats_the_best_battery

[mud4fun 1696]

16 minutes ago, Frog Jumper said:

To your comments about nicd vs nimh in terms of capacity and age, nicd has a long shelf life but not a long run time. Nimh is opposite. Read here, about halfway down..,

https://batteryuniversity.com/learn/archive/whats_the_best_battery

I do not agree with that, certainly not in my experience.

I'm not arguing with the science but I would suggest that by sheer luck more than judgement, all my NiCD's are of high quality cells whereas my NiMh's are not...... 

Yes, the NiMh's have higher capacity BUT if I divide through the number of minutes runtime I achieve on these packs into their respective capacity, my NiCd's give almost identical run times per mah, in some cases the NiCD's actually give longer run times as the NiMh's just don't seem to like heavy current draw applications such as running the 13T motors in buggies off road.

eg. My 8.4v 2000mah Sanyo packs give me 8 mins run time in a terra scorcher with a dyna run super touring motor (13t pinion). That is more than enough runtime to run a 5 minute race flat out and still have some spare. I'm quite happy to have multiple packs and change them before each race. The 7.2v 2000mah sanyo packs give my daughters thundershot (silver can) roughly 15 mins runtime, almost enough for three 5 minute races.

 

EDIT: I guess what we are all saying is that NiCd was good, NiMh was rubbish and instead of wasting money on migrating from NiCD to NiMH I might as well go straight to LiPo?