A little confused with BECs

[Charlie-III]

Originally Posted by GrimJeeper91

So does anyone actually know how many amps these these are drawing? Not just speculation, looking for published data.

I, and others, have looked for "good" info but have not found it.

A lot of us have had ESC BEC's give up when under high load with ~300inoz+ servo's. Thus they pull in excess of 5-6A.

I would love to get good info, but have not found it yet.

I know I have read that some servo's pull in excess of 10A @7.4vdc at stall.

[Charlie-III]

Originally Posted by Rig Rocker

This is such an interesting and informative tech thread! I think I need to go buy one of these so called bec thingies

I do believe McDonalds has BEC's (Bacon Egg & Cheese).....

Heck with Castle Creations, McDonalds can sell you 2 BEC's for $3.00!!!!!

[GrimJeeper91]

Originally Posted by Charlie-III

I, and others, have looked for "good" info but have not found it.

A lot of us have had ESC BEC's give up when under high load with ~300inoz+ servo's. Thus they pull in excess of 5-6A.

I would love to get good info, but have not found it yet.

I know I have read that some servo's pull in excess of 10A @7.4vdc at stall.

I've spent quite a bit of time searching...I'm glad I'm not the only one that has come up empty. I emailed JR again for info on my 8711. Will post up if I get a response.

[WIDELOAD]

Check out Welcome to ServoCity and Servo Database - RC Servo Specs and Reviews . They have most servo's listed with full specs. They unfortunately don't have the 8711 specs listed, but with some googling i found a few claims for 4amps+ at stall.

[GrimJeeper91]

Originally Posted by WIDELOAD

Check out Welcome to ServoCity and Servo Database - RC Servo Specs and Reviews . They have most servo's listed with full specs. They unfortunately don't have the 8711 specs listed, but with some googling i found a few claims for 4amps+ at stall.

That chart shows nothing more than anything else on the internet (torque, voltage, speed). It does not show the amperage at stall. Again, published data is better than some unknown on the internet saying 4 amps...

[Grizzly4x4]

Q. How much amperage does a digital servo draw?
A. It depends on the servo and the load. For standard sized digital servos, a good rule of thumb is 2A at max torque.

Digital Servos - Hitec RCD

This is all I have ever seen from Hitec, but this has been around since the 5645MG was the high end digital servo so I am sure it does not apply to todays 300+ oz-in servos.
The 5645MG is rated 168 oz-in at 6 volts so I would expect a 7955 to draw about 4 amps to make it's 333 oz-in at 6 volts.

It also depends on load. I can run my Quicksand winch (Hitec 5955 servo) and a 5955 steering servo in Guido off one 10A BEC.

However in my super I need to have two 10A BECs to run front and rear 5955 steering servos.

[WIDELOAD]

Originally Posted by GrimJeeper91

....

I said that it has the full info for most servos, but not the 8711. If you click on the servo name in servodatabase is will actually bring up more detail such as pulse width, rotation range, stall current etc. It's not listed for every servo on there, but it does have most.

As for the 'unknown on the internet saying 4amps'...If enough different people from different locations globally, and in different fields of the hobby (air, surface, here on RCC etc.) are saying that it draws 4amps. I would hazard at guess that that would be at least close to the truth or at least a minimum to work off. If in doubt add another amp or two and say it draws 5-6amps, then buy a BEC to suit.


If you don't get a reply from your email to JR and don't want to rely on some unknown on the internet. You can always make up a test rig that will stall the servo out and measure your peak amp draw.
Then you can put it up on RCC so then you can also be some unknown on the internet.

[GrimJeeper91]

Originally Posted by WIDELOAD

I said that it has the full info for most servos, but not the 8711. If you click on the servo name in servodatabase is will actually bring up more detail such as pulse width, rotation range, stall current etc. It's not listed for every servo on there, but it does have most.

As for the 'unknown on the internet saying 4amps'...If enough different people from different locations globally, and in different fields of the hobby (air, surface, here on RCC etc.) are saying that it draws 4amps. I would hazard at guess that that would be at least close to the truth or at least a minimum to work off. If in doubt add another amp or two and say it draws 5-6amps, then buy a BEC to suit.


If you don't get a reply from your email to JR and don't want to rely on some unknown on the internet. You can always make up a test rig that will stall the servo out and measure your peak amp draw.
Then you can put it up on RCC so then you can also be some unknown on the internet.

I pulled up 10 different servos in that list and not one listed stall current. Not quite sure why none of the manufacturers will publish this data.

Hopefully JR will reply this time...

[Charlie-III]

I did a Google search for "servo stall amps" and had a number of hits.

One servo (HiTec hs-5755mg) shows 4A @ 4.8vdc & 4.8A @ 6vdc.
Link..... HS-5755MG Servo
As the volts go up, the stall amps go up.

Lots more looking, not much more "real data". Did find a "rule of thumb" here (near bottom)..... Data on JR Servo Current Demands - FlyingGiants which states:
Dick Hanson has a rule of thumb that 100oz. of torque required 1 amp of power and if you look at the published specs for the various servos, that's usually pretty close.

That is probably not a bad number, but likely is relating to running amps, NOT stall amps. These are RC airplanes, they don't tend to stall servos like crawlers do.

Hmmm......maybe I should do some tests, I do have 7955's, 7950's & 7954's......

[Grizzly4x4]

Originally Posted by Charlie-III

Hmmm......maybe I should do some tests, I do have 7955's, 7950's & 7954's......

That would be cool to see.

[Charlie-III]

Originally Posted by Grizzly4x4

That would be cool to see.

Trust me, I, and others, would like to put this to rest.

[GrimJeeper91]

JR responded to my inquiry about the maximum amps at stall for the 8711 servo. Unfortunately they state that they do no have this data (hard to believe). However they do claim that it's less than 6 amps. Here's their reply: Thank you for contacting Horizon Hobby's Product Support Department. Don’t have an answer, but they way you can find it would be to take 403 oz. attached 1 inch out on an arm from the center of the output gear with an inline current meter read the current draw to lift it. We do not offer this information it should be well below 6 amps as the servo plugs will melt at 6amps. Sorry could not give you a direct answer.

[Charlie-III]

I like the "It's under 6 amps since the plug will melt at 6 amps".

It's actually a case of amps vs. time. a spike can go very high and brownout the RX but not melt anything.