Rcpilot

My Feedback: (78)

I purchased 2 of the Smart Fly heavy duty regulators. These are the ones with 18ga cables and Deans connectors coming in and going out.

On the product page, there is a calculation to determine actual continuous output:
http://www.smart-fly.com/Products/Regulator/1.htm
Amps = 12/ (V in - V out)

I am using 2000mah 6V MH batteries. They have a continuous discharge rating of 15amps.

I know the regulators are listed at 5amps continuous and 9amps surge. But if I do the math on my input and output voltage, I am coming up with 8.8 amps continuous. [sm=confused.gif] I'm cornfused.

Now, the batteries aren't REALLY 6V until they are almost dead. I don't run them below 6.1V They come off the charger at 7.4V and are still 7.3V after resting and that first flight of the day. I have the regs set for an output of 5.4V

Amps = 12/ (7.3 - 5.4)
That comes out to about 8.87 amps.

Does that mean these regs will put out 8.8amps continuous in my setup? If that is true, is it because I'm only asking them to do a little bit of work (7.3v down to 5.4V) instead of asking them to jump 13V down to 5.4?

Do the math as the battery voltage drops and the continuous amperage rating goes up even further.
Amps = 12/ (6.2 - 5.4)
That comes out to about 15 amps.

Thanks for any clarity on this.

rrritchey

Hi,
The regulators are 5 amp regulators, they will do 5 amps continuous, maybe a little more. This is a chip limitation, not a heatsink limitation. The derating is really meant for people that want to run a higher voltage than 8.4V. What the calculation is telling you is that the heatsink could support 8.87 amps at your voltages but the regulator chip will not. It has a built-in current limit that is at least 5 amps, usually 5%-20% more.
I hope this clears things up.

Rcpilot

My Feedback: (78)

Gotcha. [sm=thumbs_up.gif]

Thanks.

I need more than 5 amps continuous. Any chance of a reg with same cables and Deans connectors that will do 10-15 amps continuous?

rrritchey

Hi,
What size plane are you putting this in? This regulator will fly a 35%, 100cc plane by itself with 8411 class (220in/oz) servos. People are getting way too freaked out about servo current draw these days.

Rcpilot

My Feedback: (78)

It's 35% size with 100cc engine. Seams like 8 JR 8411 servos will draw more than 5 amps. I was hoping to supply up to 2 amps to each servo in a worse case scenario. Thats why the question about a 15amp reg.

Maybe I am worrying about nothing? It flies okay, but I can't help but wonder if my servos would be faster with more available power. Or if it would hold a knife edge at a lower rudder input? Say 15 degrees deflection instead of the 25 degrees from my stick input. It feels like I'm getting blown back on my rudder. Rather than buy 2 larger servos, I was hoping to just bump the amps available to them. Everything in the power system is designed and built heavy duty. The regs are my choke point.

Batteries have 18ga cables and Deans connectors. Switches are Heavy duty Smart-Fly with heavy cables and Deans in and out. And the heavy duty regs with 18ga cables and Deans in and out.

rrritchey

Hi,
It sounds like you have two heavy-duty regulators in your system? Are you running a PowerExpander?

Rcpilot

My Feedback: (78)

There are 2 RXs, 2 batteries, 2 switches and 2 regs. I used a Deans and soldered 3 standard servo leads to the output of each reg.

I put one lead to the Matchbox for each wing.
I put 2 leads into each RX.

With 4 JR 8411 servos on each Reg, I can deliver about 1.25 amps to each servo.

I'm using this exact same setup in a 30% plane and it feels solid. But that only has 6 servos. I added 2 more 8411 servos with the 35% plane. The 35% plane also weighs about 7-8 pounds more, so flight loads are higher.

rrritchey

Hi,
Personally I think you have more than enough regulator in this plane. You are not going to get all the regs demanding full current at the same time. I don't have a regulator that is the same form factor but has more current. Fromeco's regulators are 7.5 amp continuous, 10 amp peak regulators. I'll bet if you put heftier regs into the plane its not going to act different but I could be wrong. One thing to think about, with two standard connectors into your receiver, when the servos on the receiver are asking for 6 amps then you will have about a .25V drop from the regulator into the receiver bus. Each servo that wants 3 amps you will get another .25v drop on each standard connector. This mean if you have
1 extension to each rudder servo and it asks for 3 amps then the servo will be seeing about 5.25V instead of the 6.0V.

Rcpilot

My Feedback: (78)

Thanks for the help Robert.

I might bump the output voltage to 6.0V and see if that helps with the rudder servos. They are plugged directly into the RXs.