to "HV" or not to "HV"

Derek · Post by **Derek** » Sat Dec 27, 2014 4:20 am

Where is the line drawn where you'd "need" an HV esc? I see some motors have a max amp of 135amps on 6S and then I have the 80HV on my 600 with the 12S stock motor.

Post by **pvolcko** » Sat Dec 27, 2014 5:15 am

The primary reason you want to use an HV ESC is if you will be using power system voltage above what a non-HV ESC could handle. HV means High Voltage.

However, in my opinion, there is a case when you want the HV even if a non-HV ESC would handle the voltage you're using: when you will be pushing high current and want the extra heat sinking capability of the HV ESCs.

!!! Electronics lesson ahead: Warning, I barely know what I'm talking about!!!

Heat builds up in ESCs due to two things:

1) Current handling. Whenever current passes through a circuit it will generate heat due to resistance in the circuit. Resistance causes voltage to drop slightly through the circuit, so the waste heat is calculated the same as power: Power = Voltage x Current. Ohms law says that Voltage = Current x Resistance. So Power = Current x Current x Resistance. Assuming both a HV and non-HV ESC's circuits will have the same resistance, we can say that this source of heat build up is the same in both types and also that the heat build up will quadruple for every doubling of current flowing through the circuit. This is why high current power handling is frowned upon, it requires very low resistance circuits. If resistance isn't controlled it quickly results in high heat build up in everything the current is flowing through (batteries, wires, solder joints, circuit boards, motors, etc.).

2) Electrical switching. When an ESC switches the power on the three motor leads the transition generates a small burst of heat in the switching components (they are called FETs, field effect transistors). This heating effect is proportional to the voltage of the power the FETs are switching, meaning as voltage increases so does the heat released on a switching operation. There are thousands of switching operations per second performed by the ESC to run the motor (both on and off, on all three leads, at whatever frequency you have selected in the setup, such as 12khz). So as either frequency increases or voltage increases the heat build up due to the switching will increase too.

For #1 the heating effect is the same in the HV vs non-HV ESC assuming he same supply voltage and motor are being used. So that is a wash. Where does the added heat sinking capability come into play with an HV ESC? From #2. Because HV ESCs are designed to work with higher voltages they are designed to dissipate the additional heat generated from switching the higher voltage supply power. Assuming the HV and non-HV ESCs are rated at close to the same current handling (130A vs 120A, for instance) then the HV ESC will have some more heat sinking capability and your non-HV power system can benefit from it.

xokia · Post by **xokia** » Sat Dec 27, 2014 7:45 am

My take on this is to go with the HV esc if the costs between an HV and non HV are close to the same. An HV esc can be used at 6S. A non HV esc can not be used for 12S. So the HV esc is more flexible and gives you more options if you were to say get a different heli in the future that ran on 12S.

Graham Lawrie · Post by **Graham Lawrie** » Sat Dec 27, 2014 8:18 am

I always thought that the HV ESC was to handle the high current sudden and multiple draws associated with 3D manoeuvre s:)

Derek · Post by **Derek** » Sat Dec 27, 2014 10:34 am

Thanks guys! I think I'm understanding better what's going on.

I always thought that non-HV esc were for 6S and under, therefore HV esc's were 7S and higher. After some searching around for esc's for some upcoming projects, I was quickly confused because I was seeing motors that had a max amp of 130 on 6S. Then I was thinking about my Trex 600 and the fact that it is a 12S setup and it has the CC Ice 80HV.

Post by **pvolcko** » Sat Dec 27, 2014 4:01 pm

The usual reason for going to a 12S setup on a 550 or 600 is specifically because it allows you to go with a much lower current power system. This goes back to the power equation.

Power = Voltage x Current

So if you have a 6S 130A setup you are pushing 22.2V x 130A = 2886W of power. However, if you step up to 12S, to get the same power you only need 2886W / 44.4V = 65A.

Remember, the higher the current the more heat build up stress you put on the entire power system, so if you run high voltage on a given heli then you can bump back the current handling capability and stress the whole power system a lot less while retaining the same overall power output.

This is why the speed heli guys run 14S and 16S setups. They are pushing crazy high power so by using the highest available voltage ESCs they can reduce their current handling needs a bit and try to keep their heat build up in the motor, ESC, wiring, and batteries down to a minimum. It is much more efficient to run higher voltage, if possible.

Derek · Post by **Derek** » Sat Dec 27, 2014 4:25 pm

Again, thanks for that Paul! I've got to start remembering these equations. Maybe someday the "math" side of the hobby will stick with me and maybe I'll start to understand it better.

Graham Lawrie · Post by **Graham Lawrie** » Sat Dec 27, 2014 5:18 pm

Good explanation Paul:)

murankar · Post by **murankar** » Sat Dec 27, 2014 7:15 pm

I thought that HV was associated with the output for servos and the rest of the electrical system. Hence why servos are marked with HV. That's just what I thought.

Derek · Post by **Derek** » Sat Dec 27, 2014 7:43 pm

the HV with the servo's has to due with the higher voltages that the HV servos can run on. Most of our servos run on either 4.8 or 6.0 volts. It's when you get into the 7.2 and 8.4 volts that they consider that HV.

I've just been struggling with the comprehension on "needing" or "not needing" an HV Specific esc for two of my upcoming projects. Perhaps I shouldn't keep my projects from you guys and actually start threads on each project so that you all can help me out along the way. I was just trying to figure out "what was needed" on my own....and honestly, I'm probably just as confused now as I was when I thought up these projects.

Post by **pvolcko** » Sun Dec 28, 2014 3:44 am

HV escs typically aren't needed until 600 size helis. If you're doing some custom project then without more info on what specs you're trying to achieve can't help much more beyond the generic info above.

Derek · Post by **Derek** » Sun Dec 28, 2014 6:22 am

pvolcko wrote:HV escs typically aren't needed until 600 size helis. If you're doing some custom project then without more info on what specs you're trying to achieve can't help much more beyond the generic info above.

Yes, you are absolutely right, Paul. I'm sorry about that guys! I was just hoping that I could get from start to finish on these two projects, on my own, and then come to you all later and say, "Check this out!!!" However, I have to admit, and it's become quite clear, that I'm going to need some help from the Hangout. I have no problem admitting that, lol.

So....be on the lookout. Once I get a few details ironed out, I have two custom project that I'll be sharing with you guys. One of the projects are more realistic than the other but I can't get the image out of my head, so I'd better just go with it, lol. I got permission from the wife to go through with these projects but in order to pay for the projects, I'll have to work some overtime to fund the projects. Any money that is over my usual paycheck will go towards these two projects, so it's going to take a bit of time before they are completed....but I want to see these ideas function.

Post by **pvolcko** » Sun Dec 28, 2014 3:44 pm

Can still keep them on the down low if you want. Just need to know pertinent info. Voltage, current, motor specs, prop or rotor, vehicle weight maybe, etc. Or you can take a stab at figuring it all out and post up your thoughts and ask for a check over.

Derek · Post by **Derek** » Sun Dec 28, 2014 10:36 pm

Thanks for that reply, Paul, but I think it would just be best if I go ahead and "spill the beans" and start a thread on my project thoughts, components, and specs. I think I'll simply have faster and more productive progression with the help of the Hangout.....and potentially safer progression as well, lol.

Safety is a good thing!

cml001 · Post by **cml001** » Fri Jan 02, 2015 1:45 pm

Curious.. What's the projects? U've never been shy before Derek.. Lol.. Whatcha got kook'n? Lol

Derek · Post by **Derek** » Fri Jan 02, 2015 3:20 pm

This thread is the start of my number 2015 project. I haven't started that thread yet.

cml001 · Post by **cml001** » Fri Jan 02, 2015 3:26 pm

Lol.. Got a new one in the works myself.. Use HV.. More setup options..

Derek · Post by **Derek** » Fri Jan 02, 2015 3:42 pm

Would an 8S battery setup be considered HV? Or, where is that fine line between HV and Non HV? Or, is there a line?

Post by **pvolcko** » Fri Jan 02, 2015 3:52 pm

Depends on the esc. Castle edge max out at 8s. Personally I'd go hv on 8s.

Derek · Post by **Derek** » Fri Jan 02, 2015 5:43 pm

Maybe I just need to sit down and look at a bunch of esc's and compare the specs from one to another.

Thanks Paul!

RC-Hangout

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