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Understanding The Difference Between Nicd And Nimh Both Technically And Performance-wise

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Well, since I have gotten my Fox running, I naturally want to be able to play with it as long as possible. :) Th batteries I have are two new NiCD 7.2 packs. Both run about 10 minutes.

Should I have gotten NiMH batteries instead? I was concerned over their greater power output damaging the car. Is that something I need to worry about with NiMH? Are they really THAT much better?

However they ARE being charged off of an ancient charger (quick) which probably isn't helping much.

Any advice is very welcome! Thanks!

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Differences between nicd and nimh cells is a big subject, with numerous different opinions. However, generally speaking you will find that nicd cells are lower capacity than nimh (less runtime) but more have more punch. Nicd were most popular a few years ago, but nowadays most people go for nimh as they are more convenient. Nimh cells will not damage your car, they have the same voltage as nicd packs, and nimhs tend to be more convienient.

Nicd cells should be completely discharged before recharging to avoid the "memory effect". With nicd cells, if you don't fully charge them, after a number of charges they alter chemically and will not be able to accept a full charge. This will also happen if you keep topping them up without discharging them first. Nimh cells don't suffer this problem, and you can top them up from a partial charge with no ill effects (however I would advise with nimh cells that you occasionally give them a full discharge and recharge.

The first time you run with Nimh cells is often disappointing, but they pick up after a few charges. I've seen lots of people getting rid of brand new nimh cells because they didn't perform well for the first few runs, but if you run them a few times the performance will be as good as nicd.

I would recommend nimh cells, as they are available in higher capacity so you get more runtime, and as most manufacturers are concentrating their research on nimh rather than nicd technology, the performance of modern nimhs is generally equivalent to nicd, but with more runtime. However, if they are treated well your nicd packs will also give you years of service (I still regularly use my 4 year old 2400 Sanyo nicd packs without problems).

You are right about the charger. Invest in a good quality mid range "delta peak" charger and it will repay you with better performance, both from nicd and nimh cells. The old (older than 5 years or so) chargers are just not worth keeping IMO, as they give you limited performance and will more often than not damage your cells so they will never give their best. An investment of $100-$200 on a good charger with discharger and peak detection will more than pay back for itself over the years.

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First up, and as Jozza has suggested, get yourself a good quality peak detection charger if you dont already have one. An older clockwork charger could be causing a performance loss in your current NiCd batteries as they will not charge them completely, and could distroy the newer NiMh batteries if used to charge those.

The measure for battery capacity is "milli Amp hour" (mAhr), and the greater the capacity of the battery, then the longer the car will run for.. The capacity of NiCd batteries stops at 2400mAhr. From 2400mAhr and up they are generally all NiMh. The "nominal" voltage is the same for both, 7.2volts for a 6 cell pack.

NiMh batteries will give you longer run times, but NiCd batteries are a little more robust. As with everything, you get what you pay for. You will notice very little difference between NiCd and NiMh of similar quality, but compare the Best NiCd to the poorest NiMh (and vice versa) and you will see a performance difference.

All battery packs, both NiCd and NiMh should be discharged before recharging. These modern (IB 4200 and EP 4200 for example) batteries have a very low internal resistance, and as such, will self discharge if left for a few weeks. The cells often self discharge at different rates, and you may find that in a 6 cell pack, you have 1 or 2 cells that are completely flat, and the others partially charged. If you charged a battery pack like this, you would find that the 4 "partially" charged cells would reach "peak" voltage, and the other 2 cells that were flat may only be 3/4 charged. The 2 then 3/4 charged cells may cause the charger to not detect the peak voltage, and not turn off the charging process, causing the 4 charged cells to go into overcharge, and this could lead to the cells exploding.

One thing that you may want to consider is that running your Fox for more than 10 Mins at a time, is that you could overheat your motor, ESC etc running for longer without a break..

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Hi,

May I just come into this conversation here please? :lol:

I'm getting back into the RC Hobby (I've also posted in 'General Discussions') and I've been met with a totally new concept - the LiPO battery.

I've tried to search, but there doesn't seem to be the info I want:

How do LiPOs compare with NiCads and NiMh's? When I finished racing in 2003, NiMh's were *just* appearing. My race packs were 2400 NiCads.

So any further info on how LiPOs fit in (What are they? What's the difference in technology? etc).

Also, I've seen NiCads/NiMh's (not sure which) with capacities of 4300. How high do they go now and what are Racers using these days?

Cheers.

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The Lipo packs are lighter than the equivalent Nimh/Nicd packs. Lipo batteries are like little envelopes, and as such they are encased in a strong plastic box for car batteries, to protect them from damage. They don't need to be charged just before use, you can charge them days in advance and run them without any need to repeak. They shouldn't be run completely flat, and some ESCs have a setting for Lipo to ensure you don't flatten them. You don't need to discharge them before topping up either. They are generally a bit more punchy as they can deliver more power on demand.

However, they are expensive, and are not currently approved for racing in the UK, apparently due to the danger of fire. If they aren't charged correctly they can in theory burn, and once a Lipo is burning it sets off a chemical reaction meaning that you can't easily put it out. But at my local club there are a few people using Lipo packs and I have yet to see one go up in flames, whereas I have seen a couple of Nimh cells explode!

The Lipo packs also need a special charger capable of handling them, as the charging characteristics are a lot different than Nimhs.

Personally I still use Nimh cells as they offer the best balance between usability, price and power. They go up to 4600mah now, but I tend to stick with 3300 - 4300 capacity, the 4600 cells have had a mixed review and have a reputation for not charging well (whether that reputation is founded or not I don't know).

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Ppl are also starting to use "A123" nanophosphate cells too ;)

i think they are 3.3V 2300mAh each cell... so a 2s2c pack will give you 6.6V 4600mAh.

Main advantage is that a 2s2c (2x2) pack is same size as a 6c stick pack so it fits RC cars better

unlike the square LiPo packs... putting a plastic case around the bag LiPos is useless weight.

A123s can be charged faster than LiPos and tougher too, they're made for work tools eg DeWalt.

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