Lipos revisited

[Chegs]

Imax £14 jobby?

Yup

 

[tinyredpostbox]

if it helps (forgive me if this is telling you how to suck eggs), the mah rating is telling you that the battery is capable of supplying a certain amount of energy over time.

for instance a 1000mah battery can supply 1mA for 1000hours, or 1000mA (1A) for 1hour.

assuming that there is no energy loss to heat etc and the battery is capable of infinite constant current output, a coil build pulling 40amps from the 1000mah battery would last:

40A = 40 000mA

so

1000 / 40 000 = 0.025hours duration

0.025 x 60 = 1.5 minutes constant battery drain until it is spent.

hope this helps

 

[ambivalent]

I could be wrong here, but my understanding is that overall battery life comes down to coil resistance and therefore how much currant your pulling, rather than wattage. As 20W at 0.2 ohms (10Amp draw) =/= 20W at 1.6 ohms (1.7amp Draw) The high resistance coil extends battery life. ( I think)

Pretty sure that the battery life of your 100W mod will be much more dependant on the coil you use than anything else.

 

[fasteddie600]

Wow, busy thread!
Seedy I have just received another nice big box of 2S batteries from Hobbyking tonight, these one's might be of interest to you prob the best sized of the ones I ordered.
https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=40133
https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=29023
The 1000mAh ones are a nice size but wanted something to last a bit longer.

I also got one of these chargers from hobbyking. It looks good, but only got it tonight so not had chance to try it yet and it needs a 12V power supply.
https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=29047


1500mAh on a 2S should plenty- aprox the equivalent capacity to 2 x 18650, or, 3000mAh at 3.7V.

Hope that helps

 

[RicModMaker]

Thanks for all the advice guys. Ive seems some nice lipo packs that I'm going to go for at 1500 mah 7.4v so they will be perfect for what I need and should last longer than a single 18650 2500mah. Small sx350 100w on the way ;-)

 

[RicModMaker]

Wow, busy thread!
@Seedy I have just received another nice big box of 2S batteries from Hobbyking tonight, these one's might be of interest to you prob the best sized of the ones I ordered.
https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=40133
https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=29023
The 1000mAh ones are a nice size but wanted something to last a bit longer.

I also got one of these chargers from hobbyking. It looks good, but only got it tonight so not had chance to try it yet and it needs a 12V power supply.
https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=29047


1500mAh on a 2S should plenty- aprox the equivalent capacity to 2 x 18650, or, 3000mAh at 3.7V.

Hope that helps

Thanks Eddie. Those 1500mAh are the ones I'm interested in.
I think these are even smaller 1500mAh ones. https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=26564
For a few extra mm, these look good too: https://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=20390

 

[BaDaBooM]

Just did a quick test.

@ 13watts with the same 0.5ohm device both the 100watt and the 50watt are putting out 2.5v, same at 20watts 3.2v, at 30watts 3.8v etc until you get past 50watts.

So until you get past 50watts they are both using the same volts and amps to achieve the same watts. This means the amp draw is the same up to 50watts, so 2 batts in series is going to last as long as one single batt with the 50watt chip.





Example: 30watts 3.8v = 8 amps for both chips

Say the 50watt chip is using 2x1500mah batts in parallel and the 100watt chip is using the same batts in series. 50watts chips mah will be 3000mah and the 100watts batts will be 1500mah.

battery life = battery capacity in milli amps per hour / load current in mill amps x * 0.70

100watt chip: mah 1500 ÷ 8000ma × 0.7*= 0.13 hours
50watt chip: mah 3000 ÷ 8000ma × 0.7*= 0.26 hours

Because the 100watt chip isn't doubling the output voltage the amps are the same. Why yihi didn't double the output voltage on the 100watt chip below is strange because the batteries would last twice as long.



Id like to be proven wrong as I'm no electrical engineer but ohms law seems to be on my side unless Ive missed something.

 

[RicModMaker]

If that's the case, how come I'm getting twice as long out of the 2 batts in serial as I do on a single battery? It is half the amp draw so I'd think its pulling half the power from each cell. Am I talking rubbish? Probably ;-)

 

[ambivalent]

Just did a quick test.

@ 13watts with the same 0.5ohm device both the 100watt and the 50watt are putting out 2.5v, same at 20watts 3.2v, at 30watts 3.8v etc until you get past 50watts.

So until you get past 50watts they are both using the same volts and amps to achieve the same watts. This means the amp draw is the same up to 50watts, so 2 batts in series is going to last as long as one single batt with the 50watt chip.





Example: 30watts 3.8v = 8 amps for both chips

Say the 50watt chip is using 2x1500mah batts in parallel and the 100watt chip is using the same batts in series. 50watts chips mah will be 3000mah and the 100watts batts will be 1500mah.

battery life = battery capacity in milli amps per hour / load current in mill amps x * 0.70

100watt chip: mah 1500 ÷ 8000ma × 0.7*= 0.13 hours
50watt chip: mah 3000 ÷ 8000ma × 0.7*= 0.26 hours

Because the 100watt chip isn't doubling the output voltage the amps are the same. Why yihi didn't double the output voltage on the 100watt chip below is strange because the batteries would last twice as long.



Id like to be proven wrong as I'm no electrical engineer but ohms law seems to be on my side unless Ive missed something.

I don't think you can make a comparison like this without taking consideration of the different voltages that the batteries are using to supply the board. The 8.4 volt supply with only have to carry half as much currant to the chip as the 4.2 volt supply for an given output, I think. Its comparing apples with oranges. I stand by what I said before though, to get the best battery life from a regulated device use a higher resistance coil, higher volts and lower amps and the battery will be more efficent.

 

[BaDaBooM]

If that's the case, how come I'm getting twice as long out of the 2 batts in serial as I do on a single battery? It is half the amp draw so I'd think its pulling half the power from each cell. Am I talking rubbish? Probably ;-)

don't think you are talking rubbish I only tested it with .5ohm coil bet there is differences at different ohms.