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P-70 Kero different battery booster pack

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P-70 Kero different battery booster pack

Old 12-15-2008, 05:29 AM
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Default P-70 Kero different battery booster pack

Hello,

I had installed the stock 1250mA ECU battery on my Boomerang Intro, and built a Y connection for a booster pack just for start up. During cold days i had two put 2 additional batteries (same capacity) to get turbine ignited.
a) is it ok to use a high capacity Nicd or Nimh as Booster pack?
b) is it ok to use a Lipo 2S1P (7.4V) pack as Booster pack? i.e. mixing Nicd and Lipo's??

PS. Some would suggested upgrading ECU pack to Lipo. would eventually do so in the near future when i will be able to pull out existing Nicd pack from plane (it's glued in place and not easily accessible, beginner's mistake....).
Meatime, i need to find a quick workable solution.

Thanks for your help.
Regards.
Old 12-15-2008, 09:09 AM
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Default RE: P-70 Kero different battery booster pack


a) is it ok to use a high capacity Nicd or Nimh as Booster pack?
Yes.

b) is it ok to use a Lipo 2S1P (7.4V) pack as Booster pack? i.e. mixing Nicd and Lipo's??
No!

Old 12-15-2008, 01:31 PM
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Default RE: P-70 Kero different battery booster pack

What KC said.

a) it is OK to use a High capacity NiCd or NiMh pack of the SAME voltage as the ECU battery for a booster.

b) Never hook packs of different nominal voltages up in parallel. The higher voltage pack will try to charge to lower voltage pack up the higher packs voltage with no controls or monitoring in place. At best it could ruin one or both packs, at worst a fire or pack bursting.
Old 12-16-2008, 06:54 AM
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Default RE: P-70 Kero different battery booster pack

KC, Jeff,

Thanks for your input. Appreciated.

Regards.
Old 12-16-2008, 01:22 PM
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Default RE: P-70 Kero different battery booster pack

You should make sure you are using a pack with low cell impedance, that will ensure the higest delivered voltage whil eunder heavy load.

Regards,

Old 05-13-2010, 05:55 AM
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Default RE: P-70 Kero different battery booster pack

Did some calculations:

Internal resistance of Standard Sanyo Cadnica 1250 mah cells approx. 5 mOhms/cell. For a 6 Cell pack this is 30 mohms = 0.03 Ohms
Internal resistance of Good Lipo Cells approx. 15 mOhms/cell. For a 2 cell Lipo this will be 30 mohms = 0.03 Ohms
Total impedance of both batteries will be 0.03 + 0.03= 0.06 Ohms

Considering the worst situation when your ECU battery is less than half-charged at a voltage approx. 7.8v (1.3v/cell) and the LiPo pack fully charged at 8.4 volts there will be a voltage difference of 0.6 volts.

The current I=V/R=0.6/0.06=10 Amps

This is the worst case in an ideal world. If you ECU battery is at 8.1 volts (1.35 v/cell or approx 80% charge) your current will drop to 5 Amps which is already perfectly safe. Moreover normally your ECU batteries will have much higher internal resistance.

An easy test will be the below:
Discharge your ECU battery to below 50% charge (you will never actually fly ur jet at below 50% ECU batt charge), hook it to your charger and increase the charging current gradually till the battery voltage on the charger output reads 8.4 volts and note at which current this takes place. If this current is still within the safe charging range for the ECU battery then you can be sure that this current will never be exceeded when connecting a LiPo on the field.
Normally the maximum safe charging current for NiCd is 4C or 5 amps for your ECU battery.

If I were you I would just change the ECU battery to Lipo otherwise do the above test.

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