NiMH battery powered PVs

[Stubby]

^^this. also nimh batteries vent more violently than lithium. ive seen some go while being charged (we used to use them in rc). they sound like a 12ga shot gun when they "go off". i wouldnt want to be near it, much less in front of my mouth. if you dont fully discharge nimh batteries every cycle they will develope a memory and lose compacity (maybe not as quick in a low drain app. like an e-cig, but they still will lose compacity). your also stacking more cells to get the required voltage. your going to have risks with any battery powered device. you just need to be aware.

im not putting anyone down for using nimh. if your happy with them more power to you. what ever keeps you away from analogs.

From my understanding they are not using off the shelf AA or AAA NiMh but custom made battery packs on hobby rc toys, and who knows what they are trying to charge those things with. That is a whole different world that has nothing to do with the subject at hand. That is foolish fear mongering on your part that has no connection with reality.

There has been a few rare instances of venting and even explosion while charging, but this is avoided by using good quality batteries and charger. You don't want to buy your batteries and charger at the dollar store, but Wal-Mart is likely okay. Even then it is extremely rare. Far less then with lithium.

Your statement about memory and discharge is off the wall with BS. NiMh do not hold a memory. That myth has come about because the early NiCad did have problems with memory but that issue has been completely eliminated with modern NiHm, along with the issue of having to completely discharge, though it does show how little you know about batteries.

 

[ITPython]

^^this. also nimh batteries vent more violently than lithium. ive seen some go while being charged (we used to use them in rc). they sound like a 12ga shot gun when they "go off". i wouldnt want to be near it, much less in front of my mouth. if you dont fully discharge nimh batteries every cycle they will develope a memory and lose compacity (maybe not as quick in a low drain app. like an e-cig, but they still will lose compacity). your also stacking more cells to get the required voltage. your going to have risks with any battery powered device. you just need to be aware.

im not putting anyone down for using nimh. if your happy with them more power to you. what ever keeps you away from analogs.

I certainly wouldn't consider an ecig a low-drain device, typical atty/carto needs on average about 1.5amps. Sometimes less, but most often more.

Overall the safety reasons alone merit NiMh a better choice than Li-ions. Li-ions are very touchy and are so much more volatile. Yeah with NiMh if you don't charge them properly you may lose capacity, but if you don't charge a li-ion properly you may end up with a rocket propelled pipe bomb attached to your face.

Main reason why NiMh hasn't been adopted on with ecig stuff is because of their voltage in relation to their size. You can pack a lot of punch with a small li-ion battery, but would need something 3-4 times bigger to achieve that goal with NiMh.

Capacity though is generally better with smaller NiMh. An Eneloop AA battery can do 2000mAh on average. However a 14500 li-ion (same size as AA batt) would be hard pressed to do anything higher than 750mAh (and they aren't even doing that, even AW ones, 5-600mAh is more likely).

The main drawback to NiMh is it's size in relation to it's voltage. If ecig suppliers started making attys/cartos that were rated at about 600-800mΩ (which would equate from 1.5A to 2A current draw on the atty/carto from a fresh 1.2v NiMh) then it might be possible to overthrow Li-ions in small ecigs (although I am not sure what other complications would result of this or if even such a thing would be possible to pull off).

 

[cbrociuos]

From my understanding they are not using off the shelf AA or AAA NiMh but custom made battery packs on hobby rc toys, and who knows what they are trying to charge those things with. That is a whole different world that has nothing to do with the subject at hand. That is foolish fear mongering on your part that has no connection with reality.

There has been a few rare instances of venting and even explosion while charging, but this is avoided by using good quality batteries and charger. You don't want to buy your batteries charger at the dollar store, but Wal-Mart is likely okay. Even then it is extremely rare. Far less then with lithium.

Your statement about memory and discharge is off the wall with BS. NiMh do not hold a memory. That myth has come about because the early NiCad did have problems with memory but that issue has been completely eliminated with modern NiHm, along with the issue of having to completely discharge, though it does show how little you know about batteries.

your right. the hobby chargers we use can run a couple hundred dollars +. lol nimh batteries do develope a memory. in a pv with a very low amp draw im sure its not as much as a motor drawing 30+ amps. we stopped using nimh because you needed one pack per race, because they needed to be "cycled" after every run (charged, run 5 min, then fully discharged, or by the third race your car would be out of power 2 min. in.) lithium batteries dont have this issue. they are also able to deliver more power in a much lighter package. i have thousands of dollars in batteries and chargers in my hobby room. im not bragging im simply stating fact. so before you come on and attack someone maybe you should do some research. im not going to get into a pissing match on here. with the low amp draw of a pv nimh batteries might work great for that application, but from rc to power tools nimh is going the way of the dinosaur. for many reasons beyond power to wieght.

have a nice night. this will be my last post on your thread.

 

[Stubby]

Memory effect: If Ni-Cd batteries and Nickel Metal Hydride batteries are repeatedly charged before the stored energy is used up, the battery “memorizes” its altered, decreased lifecycle. When you use it the next time, the voltage decreases immediately. Sometimes this causes the equipment to shut down. This is called the “memory effect”.

The voltage of eneloop is higher than that of conventional Nickel Metal Hydride batteries and even if the battery is charged excessively, sufficient voltage is maintained, no memory effect occurs and you can recharge the battery according to your needs.

Refresh: This function is to remove ” Memory Effect” . This is achieved by discharging the batteries first and then recharging the batteries to its full charged. However, eneloop battery does not experience the effects of "memory effect", so eneloop does not need to use the ‘Refresh Function’.

The above is from the eneloop web site. The memory effect is largely a thing of the past with newer designs.

Trying to compare your experience with toy cars to that of e-cigs doesn't work. They are two very different applications with very different needs. I have no interest in getting into a spate, but I am interested in getting truthful information out about the differences between different battery types.

You claimed NiHm is actually more dangerous then lithium which is completely false. Quite the opposite is true as NiHm is a good deal more robust and user friendly then lithium. Having said that I do think it would be a good thing to design safety features in a NiMh based PV. At the very least short circuit protection would be a good thing. Venting would also likely be good, though how much is needed would be an area for a professional electrical engineer to say.

Hopefully we won't go down the same road as we have with lithium mods that have essential little to no built in protections, even though the need is a good deal more.