Need help with resistors or regulators?

[djs7795]

I am putting a brushless motor and esc on my helicopter. I want to use 3's lipo. The new bl main and esc will handle 3's, but the old tail esc is still brushed and cannot handle the 3's. Now to wire my new esc in i need to y splice the battery lead. So i want to know if there is a resistor, voltage regulator, or diode that will cut the voltage on the old esc battery lead by 1/3? I've been looking but i dont have the vocabulary to properly search for what i need. I've found this (http://www.digikey.com/scripts/dksearch/dksus.dll?KeywordSearch) but it is only 3 amps and i believe the 3's have closer to 18 amps. Any suggestions?

[Aethertek]

You need a regulator that will the handle the amount of current required by the tail motor only then, I doubt it is that high.
Heres a primer on their function..
http://www.southwest.com.au/~jfuller/electronics/regulators.htm
The link you provided pulls up digikey product search...scroll down to Integrated circuits(ICs), select Voltage Regulators this will take you to a search page where you can select Amps & in Features select Fixed Output... Click Apply Filters this will knock down your choices from 1400 or so to 394. You can further refine the search by again selecting Amps & click Apply filters.
Someone correct me if I'm wrong but I believe you can parallel fixed output regs without a problem if you cant find a single of the proper voltage & current level.

[djs7795]

thanks for info i think i found this one part #497-1511-5-ND on that website i linked earlier. This shows 8 volt and 3 amp should be perfect for tail motor and esc. But i dont see a maximum input voltage for this part. Will the 11.1 volt input fry this regulator? Thanks again for the help

[Trevor_G]

thanks for info i think i found this one part #497-1511-5-ND on that website i linked earlier. This shows 8 volt and 3 amp should be perfect for tail motor and esc. But i dont see a maximum input voltage for this part. Will the 11.1 volt input fry this regulator? Thanks again for the help

The number you quote is the order no. the type is LD29300V80 this is an LDO type (low drop out) these tend to be rather unstable when assulted by pulses from a BLMC.

The input voltage is OK @30V (get hold of the .pdf from the Digikey data page) but an ordinary linear regulator with thermal shutdown may be better.

Also if your input voltage is 11.1 and the output is 8V @ 3Amp the regulator will need to get rid of
(11.1-8)*3=9.9Watts. Without a massive heat sink it will fry (unless the thermal shutdown protects it).

I couldn't see a 3A 8V fixed regulator so you may need to go for an adjustable.

[djs7795]

thanks for the help guys i'll keep looking if you run in to anything please let me know.

[Markz]

Have you tried your brushed ESC on 3s? It *might* be able to handle the voltage. What kind of ESC is it?

Marc

[djs7795]

i have just ordered my bl and i am going to use my century mixer/esc to run the tail motor and my new esc and bl motor for my main. The directions for the century mixer/escx says 8.4 volt operation only. I had a eflight mixer/esc before the century. They appeared to be identical but the eflight burned up (a real flame) when i used a fully charged 9.6 ni-mh. So i got the century and only used 2's lipo has been good but i went brushless main. So i was hoping to find a resistor or regulator to put inline between the batt and old esc. The only one ive found might work but not perfect and i dont know about these adjustable votage regulators. I will probably just try the century and if it smokes go full seperates. I'll have to fiqure out how to set the revo on my tx until i get a HH gyro.

[Aethertek]

i dont know about these adjustable votage regulators
The pins have Vin, Vout & Vadj, the Vadj is set between two resistors, the value of the resistors(ratio between the two) sets the output voltage.
The first link provides a small tutorial on their use, the second a typical component & the third a good site for info. Hope this helps, good luck on the project. Circuit design is a pain but worth the effort to learn.
http://ourworld.compuserve.com/homepages/Bill_Bowden/page12.htm
http://www.national.com/ds/LM/LM138.pdf
http://www.electronics-lab.com/index.html