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Lipo 7.4v Or 11.1v?


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6 replies to this topic

#1 McHammer

McHammer

Posted 23 November 2008 - 04:10 AM

I have a TM aug with a SP130 spring and I was wondering what battery would be right for me.

I cant decide between the 11.1v and 7.4v give me your feedback!!! a-thumbsup.gif
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TM- AUG 427 FPS .2g bb
Tanaka M700 AICS in progress.

#2 cstrikeman

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Posted 23 November 2008 - 06:26 AM

QUOTE (McHammer @ Nov 23 2008, 01:10 AM) <{POST_SNAPBACK}>
I have a TM aug with a SP130 spring and I was wondering what battery would be right for me.

I cant decide between the 11.1v and 7.4v give me your feedback!!! a-thumbsup.gif

If you want performance similar to that of a 9.6 NiMh, then get the 7.4v. The 11.1v is more comparable to a 12v battery. 11.1v is going to give you better trigger response and ROF, but you're trigger contacts will wear out in no time (install a MOSFET and you're good to go with the 11.1v).
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LOL?

#3 NightWolf

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Posted 23 November 2008 - 11:05 AM

The 7.4v Lipo actually peaks around 4.24 volts per cell, making it more equivalent to the 8.4v NiMH instead of the 9.6v, so your rate of fire will be effected with this choice. The 11.1v 3S Lipo is exactly as cstrikeman stated and unless you have a switch that will handle it, a mosfet should be used. Moreover, you need to consider a charger, balancer, power supply combo as well as a Lipo Sack for safety when charging Lipo's. A $10-20 Lipo charger will not do as they have been known to fail; this is the last thing you want to happen when charging a Lipo. A good budget setup for the for mentioned items will cost you around $100, so you need to make sure you are ready for such an investment. You also need to consider where the Lipo will be mounted on the rifle. PEQ boxes and rear stocks are currently the only truly safe locations for a Lipo. Finally, be sure you invest in a quality, good name brand Lipo as with Lipos, you get what you pay for and a wise investment will last you a long time.

Carl
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#4 crusader4x

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Posted 01 December 2008 - 02:24 AM

QUOTE (NightWolf @ Nov 23 2008, 08:05 AM) <{POST_SNAPBACK}>
The 7.4v Lipo actually peaks around 4.24 volts per cell, making it more equivalent to the 8.4v NiMH instead of the 9.6v...

Not entirely true because Lipos have lower internal resistance resulting in higher discharge rates thus being comparable to a 9.6v. My 7.4v Thunder Power and Impulse Power lipos have SIGNIFICANTLY higher ROF than my 9.6v nunchuck battery.

Edited by crusader4x, 01 December 2008 - 02:25 AM.

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#5 NightWolf

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Posted 01 December 2008 - 12:04 PM

QUOTE (crusader4x @ Dec 1 2008, 02:24 AM) <{POST_SNAPBACK}>
Not entirely true because Lipos have lower internal resistance resulting in higher discharge rates thus being comparable to a 9.6v. My 7.4v Thunder Power and Impulse Power Lipos have SIGNIFICANTLY higher ROF than my 9.6v nunchuck battery.


Actually it is true...a fully peak charged Lipo that has been balanced with report between 4.21-4.24 volts per cell , depending on the charger and balancing system that was used. For a 7.1v 2S Lipo, this would calculate out to 8.42v - 8.48v and can be measured with a DVM to insure accuracy. Also note that this voltage is without a load applied, which will dramatically reflect a difference in the cells voltage output level. From your statement, you are saying that a lower internal resistance of a 7.4v Lipo results in higher discharge rates comparable to a 9.6v pack and this is incorrect. A lower internal resistance in a Lipo pack only provides a higher current output availability for the specific pack; it is the load itself (I.e.) the motor in this case, that controls the current it requires, hence the rate of discharge. If you use a motor as a constant, then it makes no difference whether you use a higher resistance, older style Lipo. or a lower resistance newer Lipo, it will make little difference in the discharge rate that you stated. The rate of discharge for both packs will remain equal under a specific load. The only difference a lower resistance Lipo has is the ability to supply a higher current within its specifications/"C" rating, but the load motor will only consume the current it needs, as it is the motor that controls the rate of discharge, not the pack.

Moreover, in order to make a fair comparison of a Lipo to a 8.4v or 9.6v NiMH, you need insure that all three are equal in the ability to supply a specific amount of current under the same load. You will find in these conditions that the 7.1v Lipo and 8.4v packs' voltage will remain more equal under load, where the 9.6v pack starts at a much higher voltage level. It is voltage level that dictates the ROF. This is where the Lipo will shine as it can maintain its level of voltage throughout its discharge cycle, where NiMHs and NiCads experience a steady, linear drop in voltage under use until drained. What you may have experienced is a higher demand placed on the battery by either a modified gun or too small of a load capacity 9.6v pack. If you over taxed the 9.6v pack, you will see a serious voltage drop in the pack under this heavy load and this will indeed effect the rate of fire, which would make the Lipo appear as if it was performing better. This is not a good reason to assume they were better, as the conditions were unbalanced.
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#6 crusader4x

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Posted 01 December 2008 - 01:45 PM

I'm not trying to be argumentative, just trying to understand and I do appreciate your explanations so please educate me!
So, as you've explained it, my 9.6v battery simply cannot supply the current the motor needs THUS making it suck compared to my 7.4v lipo? Did I get that right? Is that why my 9.6v NiMh battery can't even turn my G&P M120 while my 7.4v Lipo not only turns the motor, but does so at a significant ROF?
But you're statement was that the 7.4v lipo was more equivalent to an 8.4v NiMH than a 9.6v. A wonderfully working 7.4v lipo is NOT equivalent to a 9.6v NiMH (much less an 8.4v) that can't even turn the motor.
If it is as you stated that, "voltage level that dictates the ROF," why then do larger cells (same voltage) produce higher ROF? Why does my 7.4v have a ROF higher than my 8.4 or 9.6v batteries (all at their peak charge level) in the same gun under the same load? It would seem to me that factors other than voltage level affect ROF.


QUOTE (NightWolf @ Dec 1 2008, 09:04 AM) <{POST_SNAPBACK}>
Actually it is true...a fully peak charged Lipo that has been balanced with report between 4.21-4.24 volts per cell , depending on the charger and balancing system that was used. For a 7.1v 2S Lipo, this would calculate out to 8.42v - 8.48v and can be measured with a DVM to insure accuracy. Also note that this voltage is without a load applied, which will dramatically reflect a difference in the cells voltage output level. From your statement, you are saying that a lower internal resistance of a 7.4v Lipo results in higher discharge rates comparable to a 9.6v pack and this is incorrect. A lower internal resistance in a Lipo pack only provides a higher current output availability for the specific pack; it is the load itself (I.e.) the motor in this case, that controls the current it requires, hence the rate of discharge. If you use a motor as a constant, then it makes no difference whether you use a higher resistance, older style Lipo. or a lower resistance newer Lipo, it will make little difference in the discharge rate that you stated. The rate of discharge for both packs will remain equal under a specific load. The only difference a lower resistance Lipo has is the ability to supply a higher current within its specifications/"C" rating, but the load motor will only consume the current it needs, as it is the motor that controls the rate of discharge, not the pack.

Moreover, in order to make a fair comparison of a Lipo to a 8.4v or 9.6v NiMH, you need insure that all three are equal in the ability to supply a specific amount of current under the same load. You will find in these conditions that the 7.1v Lipo and 8.4v packs' voltage will remain more equal under load, where the 9.6v pack starts at a much higher voltage level. It is voltage level that dictates the ROF. This is where the Lipo will shine as it can maintain its level of voltage throughout its discharge cycle, where NiMHs and NiCads experience a steady, linear drop in voltage under use until drained. What you may have experienced is a higher demand placed on the battery by either a modified gun or too small of a load capacity 9.6v pack. If you over taxed the 9.6v pack, you will see a serious voltage drop in the pack under this heavy load and this will indeed effect the rate of fire, which would make the Lipo appear as if it was performing better. This is not a good reason to assume they were better, as the conditions were unbalanced.

Edited by crusader4x, 01 December 2008 - 01:56 PM.

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#7 NightWolf

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Posted 01 December 2008 - 06:00 PM

QUOTE (crusader4x @ Dec 1 2008, 01:45 PM) <{POST_SNAPBACK}>
I'm not trying to be argumentative, just trying to understand and I do appreciate your explanations so please educate me!
So, as you've explained it, my 9.6v battery simply cannot supply the current the motor needs THUS making it suck compared to my 7.4v lipo? Did I get that right? Is that why my 9.6v NiMh battery can't even turn my G&P M120 while my 7.4v Lipo not only turns the motor, but does so at a significant ROF?
But you're statement was that the 7.4v lipo was more equivalent to an 8.4v NiMH than a 9.6v. A wonderfully working 7.4v lipo is NOT equivalent to a 9.6v NiMH (much less an 8.4v) that can't even turn the motor.
If it is as you stated that, "voltage level that dictates the ROF," why then do larger cells (same voltage) produce higher ROF? Why does my 7.4v have a ROF higher than my 8.4 or 9.6v batteries (all at their peak charge level) in the same gun under the same load? It would seem to me that factors other than voltage level affect ROF.


crusader...not an issue and I am happy to help. It appears I was correct in my assumption that you were speaking of a modified rifle. Yes, I would tend to believe your 9.6v battery is not rated to supply enough current to make your setup function. However, a 9.6v battery that can supply enough current would have a higher ROF than your 7.1v Lipo. If you read my last paragraph, you would see where I specified ”you need insure that all three are equal in the ability to supply a specific amount of current under the same load.” That would not be the case in your scenario as you are trying to compare under-rated 8.4v and 9.6v cells with one that has a high enough current output that it can do the job. Equalize the test by using comparably performing NiMH’s, thus making a fair comparison and you will see where it produces the results I noted.

So, it appears you are confusing rate of fire with the "Ability to Fire". "Rate of Fire" is directly associated with the motor turning a specific rpm and these rpm’s are controlled by the voltage supplied by the pack. The higher the voltage, the higher rpm's you will turn on a motor under nominal load. This is a fact, as well as a by-product of Ohms Law that cannot change. What you are experiencing though with the cell packs is a voltage drop, usually caused by overloading the cells, since they cannot produce the higher amount of current required to run your modified system. This voltage drop would once again slow your ROF.

Any time you place a load on any battery, you will experience a voltage drop. As long as your battery is matched to the load, you will see little change in ROF. Adding a battery that cannot supply the current required will cause a slower rate of fire, so in answer you your last question, the ability of a battery to produce the current necessary to run under a give load would be an indirect factor that effects ROF. Notice I said indirect, as it is still the drop in voltage from the overload of such a battery that slows the ROF, as the cells will try to push the required current through to the motor; so once again, the voltage of the source determines ROF. Finally, if you try two batteries of the same voltage that are both more than strong enough to run the motor, the battery with the larger capacity cells will have a slightly higher ROF, as its voltage drops less under load. However, the difference is nominal and where you begin to see a wide variance is when one battery is most likely underrated, such as your 9.6v where another battery was matched for the load, I.e. the Lipo. Even the comparison with a better grade 9.6v pack and you will be surprised at the results.

Edited by NightWolf, 01 December 2008 - 06:02 PM.

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