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Thread: nimh and lipo

  1. #1
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    nimh and lipo

    Regarding a 8cell 9.6v nimh 5000mah and a 2s lipo. The 9.6v nimh has more speed and acceleration compared to the 2s lipo. In my opinion if you are going with the 2s you might as well go with this nimh. Which is safer. I mean why go half way just get the 3s if you are going lipo anyway. Maybe someone has a say on this.

  2. #2
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    Lipo power is MUCH cleaner! holds it power on a much longer curve. But, you're talkin about 7.4v vs. 9.6v. Sure you're going to have more power - but it will tail off much faster and you'll loose the juice sooner

    I get my 2s 4000 lipos for $18.00 plus shipping and my 5000s for 23$. how much are you paying for a 9.6v nimh?

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    Lipo is better it last longer.

  4. #4
    Marshal Dadx2mj's Avatar
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    There is more to consider than just top speed. Lipos hold their voltage better and have a flatter discharge curve and lipos are lighter and improve handling because of it. Also quality nimh cells are getting harder and harder to find especially at a reasonable price.

    It is also somewhat of a misconception that is readily accepted that nimh require less maintenance. IMO they actually require more. A nimh cell should be balanced just a lipo is but since not all packs can be balanced and it requires more specialized equipment to do so most people simply dont. Lipos can go onto a charger immediately after a run, a nimh should not as it needs to cool before it can be recharged.

    Nimh are slowly fading away just has the nicad before them did, lipo has become mainstream and the cost are low enough now they really are the best all around option.
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    Quote Originally Posted by Dadx2mj View Post
    There is more to consider than just top speed. Lipos hold their voltage better and have a flatter discharge curve and lipos are lighter and improve handling because of it. Also quality nimh cells are getting harder and harder to find especially at a reasonable price.

    It is also somewhat of a misconception that is readily accepted that nimh require less maintenance. IMO they actually require more. A nimh cell should be balanced just a lipo is but since not all packs can be balanced and it requires more specialized equipment to do so most people simply dont. Lipos can go onto a charger immediately after a run, a nimh should not as it needs to cool before it can be recharged.

    Nimh are slowly fading away just has the nicad before them did, lipo has become mainstream and the cost are low enough now they really are the best all around option.
    Ok . I run traxxas Nimh power cell 9.6v and they are over 2 yrs old and still going strong and Hv 2 traxxas 11.1v 3s lipos that I haven't run yet , I lost a 11.1 spc lipo after 4 months and balance charge every time . IMO lipos are more fussy how they're maintained than Nimh .
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    Quote Originally Posted by rhardy60 View Post
    .... IMO lipos are more fussy how they're maintained than Nimh .
    As Dad pointed out in his post above, properly caring for a Nimh pack is more difficult and I agree with that fact.

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    Quote Originally Posted by Jakey View Post
    As Dad pointed out in his post above, properly caring for a Nimh pack is more difficult and I agree with that fact.
    I just don't under stand how lipos are easier . I'm new to lipos so i don't no anyone that has a lipo over 2yrs or older do you ? I also hv Nimh over 3 yrs an still going .
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  8. #8
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    Quote Originally Posted by rhardy60 View Post
    I just don't under stand how lipos are easier . I'm new to lipos so i don't no anyone that has a lipo over 2yrs or older do you ? I also hv Nimh over 3 yrs an still going .
    For LiPo the entire charge cycle is controlled with a CCCV regime and the ESC prevents over-discharging as long as the LVD is activated. Nimh is very picky about overcharging and requires correct charger delta V settings to prevent overcharging. And Nimh is even worse when it comes to over-discharging as the cells have a very high self-discharge rate plus they self-discharge at dissimilar rates, making individual cell equalizing virtually mandatory for good pack life. Then there is the fact that due to their lower average cell voltage, a Nimh pack requires 3 to 4 times as many cells as does an equivalent voltage LiPo pack. Statistically this places even more maintenance on Nimh.

    You posted a couple months ago of problems with a Traxxas LiPo pack and now mention problems with another LiPo. Sadly you probably do not understand RC LiPo battery packs.

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    I've had nimh get so hot they melted the shrink wrap and on one occasion vented. Never had an issue with a lipo doing anything like that. Lipos got a bad reputation because when they do vent it is VIOLENT, when a nimh vents not nearly as much. I think this is why we take care of lipos better and equipment is readily available to do that. It does not mean nimhs dont need the same care just that we tend to not be as nervous about it. Now days a lipo charger almost always comes with a balancer yet few RC hobbyist even know what a balncing tray is (balancer for nimh packs) and they will only work on packs in side by side configuration.

    Bottom line nimh are fading into oblivion and lipo has become mainstream. Has this trend continues a good nimh pack is getting harder and harder to find and you will pay more for it. Plus as brushless systems become more powerful nimhs just cant keep up. Try running a amp hungry 4 pole motor on even a good nimh and see what happens.
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  10. #10
    RC Turnbuckle Jr. harry697's Avatar
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    Quote Originally Posted by Jakey View Post
    For LiPo the entire charge cycle is controlled with a CCCV regime and the ESC prevents over-discharging as long as the LVD is activated. Nimh is very picky about overcharging and requires correct charger delta V settings to prevent overcharging. And Nimh is even worse when it comes to over-discharging as the cells have a very high self-discharge rate plus they self-discharge at dissimilar rates, making individual cell equalizing virtually mandatory for good pack life. Then there is the fact that due to their lower average cell voltage, a Nimh pack requires 3 to 4 times as many cells as does an equivalent voltage LiPo pack. Statistically this places even more maintenance on Nimh.





    Quote Originally Posted by Dadx2mj View Post
    I've had nimh get so hot they melted the shrink wrap and on one occasion vented. Never had an issue with a lipo doing anything like that. Lipos got a bad reputation because when they do vent it is VIOLENT, when a nimh vents not nearly as much. I think this is why we take care of lipos better and equipment is readily available to do that. It does not mean nimhs dont need the same care just that we tend to not be as nervous about it. Now days a lipo charger almost always comes with a balancer yet few RC hobbyist even know what a balncing tray is (balancer for nimh packs) and they will only work on packs in side by side configuration.

    Bottom line nimh are fading into oblivion and lipo has become mainstream. Has this trend continues a good nimh pack is getting harder and harder to find and you will pay more for it. Plus as brushless systems become more powerful nimhs just cant keep up. Try running a amp hungry 4 pole motor on even a good nimh and see what happens.

    Agreed 100%. While I have owned nimh packs in the past that performed pretty much identical to 2S lipo packs in 2wd 1/10th vehicles, not only are they all but non-existent these days, but they also required more attention. Not only did I use the LVD on my esc when running extended lengths of time on nimh to prevent damage from over-discharging, but I also had to buy a high-end charger to prevent damage from over-charging and also had to carry around a balancing tray to keep all 6 of the cells balanced properly. Oh, and when was the last time your lipo pack came off the charger at 125 degrees? That was kinda the standard for nimh cells.

    As far as the danger factor goes, I have still never seen a lipo fire in person. I've seen them swell up like pillows, but never vent. On the other hand, I've seen and heard plenty of nimh cells pop at the track. One day I witnessed an expensive EP4600 nimh pack blow the end off of a cell right in front of a guy's face! I was pitted right behind him and the sound was like a gun shot. We never did find the cap from that cell. Probably ended up somewhere in the lot behind the track.

  11. #11
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    Quote Originally Posted by rhardy60 View Post
    I just don't under stand how lipos are easier . I'm new to lipos so i don't no anyone that has a lipo over 2yrs or older do you ? I also hv Nimh over 3 yrs an still going .
    I've got one with an 08/08/08 date on it. I marked it when I received it. Happens to be of the SPC Racing variety.
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  12. #12
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    Harry I agree with you 100%. I've gone to lipo and haven't looked back. On the lipo fires I've seen 1 and heard about another 1 at a track I frequent within 2 months of each other. 1 was bad enough it set off the fire sprinkler system as it was in a pit suite.

  13. #13
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    I have several lipo packs that are 4-5 years old and are still working fine. These are from my helicopter and airplanes. They have been around for a long time before the car guys found out about them. Its funny but the lipo's for the ground r/c's don't seem top last as long as they do in air r/c.. most likely because of the pounding they take as well as the increased demands put on them from the high current applications we run. I've had 3 ground lipo's go bad in the last year and two of them were wires breaking off internally and the last one recently I can't get the 3rd cell to balance..
    As for Nimh batteries. I still have a few that I use in my young daughters Tamiya TT01's but only because they don't need anything else and the cars don't have any form of LVD and my girls can't be trusted to stop running the cars when they see them getting slower. I have to go thru quite a procedure with these batteries to get them to fully charge and hold the charge and I have the chargers to do so.. It really is a pain, although years ago it was an accepted norm. With Lipo's. just set the charger and balance the batteries during charging and you are set. They are not dangerous if used correctly. I've personally seen Nimh batteries burst. I blew one up during charging but never had a lipo burst. I did have one puff a bit a couple of years ago but I still fly with it and it holds a full charge to this day. I wouldn't recommend that for a ground vehicle but in a plane its not really being abused much.
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  14. #14
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    Really good quality nimh cells like Dad said are getting hard to come by. Care and feeding of nimh is cumbersome. I love my 9 cell pro-match custom built pack but it's twice as heavy as a 3s 5000mah lipo. It's heavy enough it took some doing to make my Rusty handle with that much mass on board. That being said, I had some lesser quality packs built with tenergy cells that split the pack's shrink wrap and the cell's shrink wrap. It was pretty hot and some of it was my choice in gearing that might have nuked a lipo too. Still I've had others like production venom packs that blew up cells on just 6 cell packs.

    I've seen one lipo puff but not explode or catch fire. The biggest thing is regardless of cell type, you can kill either type by misuse and improper gearing. Neither are pretty if they pop.

    Voltage is one of those things that the more you have, the faster it will go. But when you factor the weight difference the lipo with lesser voltage at 2s is similar to a 7 cell nimh pack. Go up to a 8 cell pack for 9.6v and it will be initially faster but won't hold it's advantage long. Weight starts negating the voltage advantage making it a heavier handling car. I've got A LOT of full throttle time with many 9 cell nimh packs (all custom built) and none of them could beat a rusty with 3s power in a drag race. The weight helped keep the front end down but it slowed initial acceleration compared to a lipo.

    That's only factoring voltage and weight. Add in the fact that the discharge curve is flatter on a lipo vs nimh means you have the same strong power from right off the charger through most of the pack. You can't say that for nimh.

    Lipos just make it easy. Plug in the balance tap on the charger and charge it. Run it until the lvc kicks in and repeat. Gear it right and the pack won't nuke itself.
    Brushless 9cell/3s Street Rusty

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