RE: lipo or nimh  
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RE: lipo or nimh - 5/13/2008 3:28:01 AM   
Access


 

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From: , CA, USA
Status: offline 		Yeah CC-CV charge not CC charge like with NIMH, so a 1C charge can actually take almost 2 hours. It has to ramp down at the end, after 1 hour it might be 80% charged though. As the battery ages or is abused it starts to take longer an longer, a new battery might only take 1.5 hours.

As for LiPos I hear the 'zippy' ones on that site are okay, never used them myself though.

< Message edited by Access -- 5/13/2008 3:29:57 AM >

(in reply to AutoXMan)
       Post #: 26

RE: lipo or nimh - 5/13/2008 4:06:02 AM   
AutoXMan



Posts: 4366
Joined: 1/12/2006
From: Trumbull, CT, USA
Status: online 		That could be the case with your charger, but some of them only ramp down the charge rate right before it is done charging. My batteries never take more than 1 hour to charge at 1C rating, because I never run them down past 20% to begin with.

(in reply to Access)
       Post #: 27

RE: lipo or nimh - 5/13/2008 4:41:10 AM   
Access


 

Posts: 2305
Joined: 3/8/2005
From: , CA, USA
Status: offline 		If it is a true CC-CV charger it should do what I described. At no time should the voltage go above 4.2V, once it hits 4.2V it should kick back into CV mode. If it doesn't do that, you are shortening the life of your batteries a lot and, in the worst case, it can be dangerous.

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RE: lipo or nimh - 5/13/2008 5:17:26 AM   
astroboycp



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From: , SINGAPORE
Status: offline 		Maybe can try those new A123 batteries. They seem to be safer than lipo as that's what they claim.

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       Post #: 29

RE: lipo or nimh - 5/13/2008 10:56:14 AM   
Lilredmachine


 

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Status: offline 		Problem with NIMH is that you will only ever be able to pull 40-45 amps out of them, expensive cells or not. On startup a brushless motor will try and pull over 100 amps, and if it can't get it, you'll lose punch. That's why Lipo is the preferred battery for brushless, whilst NIMH is perfectly adequate it's not ideal.

Venom Lipos are excellent, I run them in my E-savage and they give so much punch it's unbelievable, rated to 100amp continuous.

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RE: lipo or nimh - 5/13/2008 12:39:28 PM   
AutoXMan



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quote:

ORIGINAL: Access

If it is a true CC-CV charger it should do what I described. At no time should the voltage go above 4.2V, once it hits 4.2V it should kick back into CV mode. If it doesn't do that, you are shortening the life of your batteries a lot and, in the worst case, it can be dangerous.


Yep at 4.2 volts it should be fully charged so once it hits that (at about an hour) it should be done.

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RE: lipo or nimh - 5/13/2008 1:03:33 PM   
SPC Racing


 

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quote:

ORIGINAL: Lilredmachine
Problem with NIMH is that you will only ever be able to pull 40-45 amps out of them, expensive cells or not. On startup a brushless motor will try and pull over 100 amps, and if it can't get it, you'll lose punch. That's why Lipo is the preferred battery for brushless, whilst NIMH is perfectly adequate it's not ideal.

Venom Lipos are excellent, I run them in my E-savage and they give so much punch it's unbelievable, rated to 100amp continuous.

We've tested Nimh cells and packs at rates up to 80-Amps continuous and 100-Amp bursts with no problems at all. I would like to test your Venom LiPos at their claimed 100-Amp continuous discharge rate.

< Message edited by SPC Racing -- 5/13/2008 1:04:29 PM >

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RE: lipo or nimh - 5/13/2008 1:14:17 PM   
AutoXMan



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quote:

ORIGINAL: SPC Racing

We've tested Nimh cells and packs at rates up to 80-Amps continuous and 100-Amp bursts with no problems at all. I would like to test your Venom LiPos at their claimed 100-Amp continuous discharge rate.


Venom LiPos are top-notch, I have been using them for a few years now, I trust their claims.

As a distributor (or manufacturer) it is interesting to see how you have to go after other companies.

(in reply to SPC Racing)
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RE: lipo or nimh - 5/13/2008 1:25:39 PM   
SPC Racing


 

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quote:

ORIGINAL: AutoXMan
Venom LiPos are top-notch, I have been using them for a few years now, I trust their claims.

Good for you, I'm truly glad you like them.
quote:

ORIGINAL: AutoXMan
As a distributor (or manufacturer) it is interesting to see how you have to go after other companies.

Wow! You read a lot more into my statement than was intended. I would still like to perform a 100-Amp continuous discharge test on the Venom LiPo pack noted. Do you know the exact pack Lilredmachine was talking about? Maybe I'll purchase one for testing.

< Message edited by SPC Racing -- 5/13/2008 1:27:38 PM >

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RE: lipo or nimh - 5/13/2008 1:34:09 PM   
AutoXMan



Posts: 4366
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Status: online 		Lilredmachine is probably talking about this pack...

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXTCE1&P=ML

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RE: lipo or nimh - 5/13/2008 1:41:14 PM   
SPC Racing


 

Posts: 40
Joined: 7/2/2007
From: Lewis Run, PA, USA
Status: offline 		Thank you!

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       Post #: 36

RE: lipo or nimh - 5/13/2008 4:13:43 PM   
Access


 

Posts: 2305
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From: , CA, USA
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quote:

ORIGINAL: AutoXMan


quote:

ORIGINAL: Access

If it is a true CC-CV charger it should do what I described. At no time should the voltage go above 4.2V, once it hits 4.2V it should kick back into CV mode. If it doesn't do that, you are shortening the life of your batteries a lot and, in the worst case, it can be dangerous.


Yep at 4.2 volts it should be fully charged so once it hits that (at about an hour) it should be done.

Hmm, I don't think we're on the same page here, it is not done once it hits 4.2V, once it hits 4.2V you still have to wait for the charge current to drop to 10mA. If you don't do that you are missing out on about 20% to 30% of the charge. At 1C you can charge your LiPos about 70% - 80% in about 45 minutes, but to get a truly 'full' charge it will take you about 1 hour 30 minutes.

As for the venom LiPos they are more than decent, much more than I can say for the venom NIMHs. I tested a 3s pack and posted the plots here:
http://www.rcuniverse.com/forum/m_7001137/anchors_7001137/mpage_1/key_scope/anchor/tm.htm#7001137
And it was superior to one of the older maxamps packs I had tested (not the maxamps HV packs).

< Message edited by Access -- 5/13/2008 4:14:32 PM >

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RE: lipo or nimh - 5/13/2008 5:35:50 PM   
AutoXMan



Posts: 4366
Joined: 1/12/2006
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Status: online 		Yeah I guess we are talking about different things.

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RE: lipo or nimh - 5/13/2008 6:03:30 PM   
Access


 

Posts: 2305
Joined: 3/8/2005
From: , CA, USA
Status: offline 		If you are using a charger like the Intellipeak ICE (the one I use) this is how it works.

1) CC charge until the battery reaches 4.2V. (~40 minutes)

The ICE gives you a double tone at this point. If you are really pressed for time, you can go now, as the battery is typically 70% - 80% charged at this point.

2) CV charge until the current drops to 10mA. (varies)

When this is complete the ICE gives you the 'finished' tone and you are ready to go.

3) "trickle" charge until current drops to 0mA. This gives you a few more mAH but not a significant amount.

When this is complete the ICE gives you a single tone and stops.

As the battery gets older, or if it has been frequently abused, the time spent in (1) drops and the time spent in (2) rises.

If your charger does only step (1) and not (2), you are not getting a full charge, you are only getting about 80% of the full charge.

Mind you this isn't necessarily a bad thing, espeically if you only run your cells down to about 30%. If you start at 80% and run your cells down to 30%, you will get more than double the cycle life than if you start at 100% and run your cells down to 0%.

An electric car like the Tesla gives you this option, if you know you are only going to drive twenty minutes tommorow, there is no point in charging your batteries beyond the 60% or 70% point. Since charging the batteries fully (to 100%), or discharging them fully (to 0%) creates the most wear. Running them in the middle regions, 25% to 75%, creates significantly less wear (even for 2 cycles) than a single full cycle.

Hopefully I didn't confuse anymore more with that explanation...

(in reply to AutoXMan)