ESC ratings for brushed motors.

[Martin Field 1Participant @martinfield1]

Need to know the Amps

[Martin Field 1Participant @martinfield1]

Hi,

I am getting back to my model boats because it may prove difficult to fly with the coming restrictions, whereas I have water all around me I can use.

I have a few brushed motors ranging from the smallish ex flight motor, the speed 400 size, to the types used in electric drills and those I believe are called 540s. I have no idea what amperage rating I need in ESCs for these. I have a couple of big Chinese things and a Simprop 20A already. My brushless motors have been pressed into use in my model aircraft, so I may as well use up my brushed motors in my scale vintage mahogany "hot rods" and British speedboat models. I'm not interested in the demented duck kind of performance.

Many thanks for your help.

Martin

[harry smith 1Participant @harrysmith1]

Hi Martin

I use the Quicrun 60 Amp car/boat (with reverse) for 2 and 3S Lipo with link setup.

Simple,cheap and easy to use.

The 540 brush motors 35turn 13000 rpm on 7.2 volts(2s), 45turn 9500 , 55turn 7700, 65 turn 7000 and 80turn 5500 rpm( rpm is unloaded).

If your require rpm on 3S divide the rpm by 7.2 , then times that by 11.1 for the rpm on 3S.

The same if you require the kv rating on changing to brushless.

Rpm divide by volts equals kv !!!

Harry Smith

[Chris EParticipant @chrise]

I am afraid that there are so many variants of both 400 and 540 motors that there isn't a simple answer. This is the problem of using unidentified motors.

To get an answer you need to know your supply voltage and how many amps the motor will use with your intended propeller. It also helps if you know the stall current of the motors at your desired voltage.

Ex drill motors are often not suitable for model boat use because they are such high rpm motors.

As a flyer I am guessing that you have a wattmeter. It is time to use it!

[ashley needhamParticipant @ashleyneedham69188]

As above, use a wattmeter, it’s the only way to sort out your query.

Ashley

[Ray Wood 3Participant @raywood3]

Welcome back Martin,

My non technical approach is 15amp for a 400 brushed motor & 20amp for a 600 seems to work for me 😀

Regards Ray

[Chris EParticipant @chrise]

Ray's approach isn't what I would do but I can see the appeal. If you are going to proceed this way then a fuse of well below the Esc rating becomes even more important than normal.

The problem is that some variants of 400 & 540 can motors will run at 25% of the revs of others on the same battery. The propeller size that they can drive is obviously very different. If you guess wrong at one extreme you might have very little thrust and at the other a current draw that could blow your esc and at the same time a wildly overheating motor.

[Malcolm FraryParticipant @malcolmfrary95515]

The nce thing about brushed motors is that you don't need an ESC to check what current they take. Just get a bag of assorted fuses and connect them to the battery under load. Take the lowest value fuse that doesn't blow, pick an ESC of a higher current rating (preferably start at fuse + 50%) and it will work. If using a meter to check the current, start at 50% more than the reading.

[redpmgParticipant @redpmg]

Clever thinking Malcom – but what about voltage . Have 385's for instance that happily run off 6v and other 385s that come out of hairdryers which need 12v to perform . 280 case might enclose a proper brushed motor – another has simple brass plate brushes – one takes about 3v the other up to 7.2 and one I have is happy on 12v. . The variance on 400 & 500 type motors is enormous too. Even the 545's come with very different windings & values

Somewhere on the net is a chart of Mabuchi markings which would give you the correct voltage at least – most of the other manufacturers use the same chart which helps . I have it downloaded somewhere on my other PC if you wanted it – might take a while to find……….

[harry smith 1Participant @harrysmith1]

Graupner and MFA have charts you can download.

540 rock Crawler motors have specs, but mainly on 7.2 volts(2S Lipo batteries).

Harry Smith

[ashley needhamParticipant @ashleyneedham69188]

If the motor is unmarked its a bit tricky to guess its voltage rating, but wattmeters can be had at Component shop for 10 or 18 quid (30 or 150A) and are well worth the small cost.

Invaluable when dealing with the unknown!!

Ashley

[Chris EParticipant @chrise]

I totally agree with Ashley. I had assumed that as a flier your would have one but if not then get one.

The other thing you should know about a motors is it's kv. That is how many revs they do per volt of input.

This can be measured either with an optical tachometer and a strip of card sellotaped to the motor output shaft like a small propeller using a relatively low voltage battery. (Revs/volts = kv)

or by driving the motor at a known speed (electric drills often specify their speed) and measuring the voltage that you get across the motor terminals. (say 1000rpm gives 2v then kv = 1000/2 = 500kv)

[Martin Field 1Participant @martinfield1]

I do have a watt meter, but no idea how to wire it in to things and I have a tacho too, which I've never used. I thought Kv was only a brushless thing and I'm dealing only with brushed motors here. The one I'm using is a standard, unpainted casing 380 type size which came out of a light powered glider, using a "brick" R/C system which has everything on one board, Rx. ESC and linear servos, so I doubt there's much amperage involved for an ESC. I have a 20Amp ESC, marked as such by Multiplex and the Chinese thing with the ally heatsink which has no markings at all, but is fairly beefy with hefty wires in and out. Also has a switch lead, too.

I now have XT60 connector soldered to the battery end and a Deans on the motor end and on the motor (as I had a load). My extra Flysky 3 channel Rxs arrived a few minutes ago, so I shall give it all a go and see what happens. I shall check the voltage on the Rx. lead of this ESC too before plugging it in to the Rx.!

Thanks for your help, gents.

Martin

[Chris EParticipant @chrise]

All motors have a kv value regardless of whether brushed or brushless. It is just that brushless buyers want to know what they are buying which doesn't appear to worry many brushed buyers who often buy from a very restricted range of motors that they are familiar with. (ducks ready for the assault). Not knowing the kv works if you know the motor anyway and what it will do ie MFA 385 or 540.

Your watt meter is a very useful bit of kit. You can connect it between that battery and any user of power – motor – servo etc to see what is happening. I generally connect it between the battery and the esc. It should have connectors marked "in" (battery) and "out" (esc/motor etc). You will obviously need to have plugs/sockets on the leads that make this possible. It will then tell you the battery voltage and the amps/watts that you are using. This not only tells you about the motor but also tells you about how happy your battery is.

The optical tachometer reads revolutions.

If I have an unidentified motor the way that I use mine is to attach, using sticky tape, a piece of dark (brown, black etc) card to the output shaft of the motor when it is out of the model. It should look like a narrow 2 blade prop. You then use the tachometer to look through the spinning blades at a bright source of natural light. This will tell you how many revs the motor is giving from the battery that you have connected. The only thing to bear in mind is if it wasn't meant for model use it will read double the revs because two blades pass the sensor each revolution. I suggest wearing glasses for obvious reasons.

The reason for natural light is that mains electricity runs at 50Hz and, particularly with fluorescent tubes, that can crate havoc.

To use the tachometer in the model I just use a piece of white card wrapped around the coupling. I stop the card falling off with a strip of black dark tape in line with the motor and propshaft that also stops the coupling rotating inside the card. You need the card sleeve to rotate at the same speed as the propshaft!  You need as much natural light as possible falling onto the card. Your tachometer will now read the revs correctly as there is only one black line per revolution.

If you combine the wattmeter & tachometer readings you are now well on the way to understanding what is going on with any motor/battery/prop combination.

Edited By Chris E on 12/09/2020 17:08:34

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