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Which relay should I use?

Maxwell

Oct 1, 2016
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These motors are called brushless dc motors that look like that:
https://www.aliexpress.com/item/Hig...2695068434.html?spm=2114.40010208.4.40.nitm3o
It's not the exact one but that is the idea.

If they take DC then how come it's not DC inside the motor?

Because they have an inverter that turns the DC into a sort of AC. Owing to the brushless design they need to alter their current in order to work.

So help me understand how you are wiring this motor then... The motor has 3 wires going into it? How are those hooked up to the battery (which is clearly DC, ie, 2 wires). The way i see it you should only have 2 wires going to the motor or the inverter, and then 3 for the coils internally, you want to splice into those?
 

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*facepalm*. The controller produces the 3 phase AC to drive the motor.

So the AC voltage rating on the relay is important. However, stopping drive to the motor to reconfigure is still a good idea.

Placing I inside the housing of the motor though... That may be a tough ask. How much room is there?
 

roig12

Oct 29, 2016
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*facepalm*. The controller produces the 3 phase AC to drive the motor.

So the AC voltage rating on the relay is important. However, stopping drive to the motor to reconfigure is still a good idea.

Placing I inside the housing of the motor though... That may be a tough ask. How much room is there?

It will be tight and neat but there is some room, it's a big motor.

So DC relays are not good for me?
and if I need AC relays, can I use ones that are intended for 220v (mine is 88v, is it still 88v when turned into AC?)
and what about the amp rating of the AC relay, my controller pulls 45A from the battery, so do I have to have a minimum of 45A AC relay or should I just multiply the 88v by the 45A to find the total watts and as long as the AC relay voltage rating times amp rating is above my controller watts then I will be fine?
 

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No, the relay coil should still be DC, but the contact ratings can be those for AC, which for a given relay is typically much higher.
 

duke37

Jan 9, 2011
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You are getting mixed up between the energising voltage and the maximum permitted switched voltage/current.

The relay needs 48V +/- to switch. Connecting two in parallel still means 48V. Connecting two in series will need 96V so your 88V may not be enough particularly when the supply is under load. This wll need to be fed with DC.

The switching capability is 30A on 250V AC or 30V DC.
 

roig12

Oct 29, 2016
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Ok, this makes more sense now.
I will be connecting them in parallel so 48v to trigger it, so can I use 88v to trigger it or will it fry and I will have to use 48v max?

So can I use this one that I posted (the T90 30A)? two relays in parallel for each phase wire? and it will be able to handle the voltage since it's AC inside the motor right?

EDIT: Now that I think about it, do I have to parallel two? why not use one? yes I'm using 45A while the relay is rated for 30A but I'm using the third of the voltage (88v instead of 250v which is the max), so in watt terms it's still lower than the max 250v*30A since I'm using 88v*45A
Am I right here?
 
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No, you must not exceed the current rating.

Or the voltage rating.

And you can't trade one off against the other.

However, if you have access to the datasheet it may have a different carrying current to the breaking current. If the current falls when you switch and you stay within the specs you may be ok. But you must be guided by the specs.
 

roig12

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Ok so bottom line I should parallel two of the above relays for each phase because I now understand that the voltage inside the hub motor is actually AC which two in parallel give me more than enough while the DC is only 60v (I need 88v), am I right?
500v AC or 60v DC at 60A (all data double because paralleled) and I'm putting in 88v (apparently AC) and 45A so I'm within spec, correct?

btw, I need a 5 pin and the cheaper ones are 6 pin and from what I understand it's the same only the com pin is there twice (in the 6 pin) so I use only one right?

About the coil voltage, if it's 48v, should I use 48v or up to 48v? if I use for example 24v will it turn on?
 

Maxwell

Oct 1, 2016
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IT might, or then it might not. If a relay needs 48v to turn on, then it's better to use 48V, you might also want to have some sort of control circuit to make sure the voltage does not exceed 48v, but that sort of depends on how stable the voltage is to begin with.

So getting back to the switching part, you just need a relay that has an NC and NO contact. Then you can hook up the star point to the NC contact and wire the L1, L2 and L3 to the NO contact, then when the relay is energized, it will switch from star to delta configuration. You'll have to make sure the phase angle is correct, otherwise you'll be going 110 in reverse.

Also, i don't have much experience with DC brushless motors, but i do have some experience with AC induction motors, and switching them from star to delta means they will be getting the input voltage times SQRT 3... so 150v , are you sure the motor can handle that?

Finally, you will be needing to access the wires coming from the controller to the motor, not the ones going into it.
 

duke37

Jan 9, 2011
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Paralleling relays will not increase the voltage capability, just the current that can be handled but you may have trouble if one relay opens a fraction of a second before the other. The second relay to open will have to break the total current.

If there are duplicate pins, then use both to get the lowest current through each and the best cooling.

I doubt if 24V (50%) will pull in a 48V relay but may hold it in, use 88V and a series resistor but you could try two in series on 88V (92%).

You asked earlier what a contactor is. These normally have a big copper bolt for input and another for output. To make a connection a copper bar is pulled between the two and a strong spring is used to open when the contactor is unenergised. Arc control is incorporated as mentiond before.
To do wye to delta switching, the contactors are cross coupled so that both contactors cannot be energised together. Often this cross coupling is also done mechanically. They do not have back contacts except for a low current one for cross coupling protection.

You may be able to manage with a three pole changover relay.
 

roig12

Oct 29, 2016
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IT might, or then it might not. If a relay needs 48v to turn on, then it's better to use 48V, you might also want to have some sort of control circuit to make sure the voltage does not exceed 48v, but that sort of depends on how stable the voltage is to begin with.

So getting back to the switching part, you just need a relay that has an NC and NO contact. Then you can hook up the star point to the NC contact and wire the L1, L2 and L3 to the NO contact, then when the relay is energized, it will switch from star to delta configuration. You'll have to make sure the phase angle is correct, otherwise you'll be going 110 in reverse.

Also, i don't have much experience with DC brushless motors, but i do have some experience with AC induction motors, and switching them from star to delta means they will be getting the input voltage times SQRT 3... so 150v , are you sure the motor can handle that?

Finally, you will be needing to access the wires coming from the controller to the motor, not the ones going into it.

About the wiring, shouldn't it be star point to NC, delta point to NO, COM to controller phase wire and the coil + and - to a 48v power source with a switch?

Are you sure about the voltage? is it the same with DC motors? btw, why is it called a DC motor if inside the motor it's actually AC?
The motor can handle that for a short period, it's about 6700 watts but I hope it isn't so with the voltage raise.
http://www.allaboutcircuits.com/tex...t/chpt-10/three-phase-y-delta-configurations/
Quote from that link:
"In balanced “Y” circuits, line voltage is equal to phase voltage times the square root of 3, while line current is equal to phase current. In balanced Δ circuits, line voltage is equal to phase voltage, while line current is equal to phase current times the square root of 3."

Does it mean that in star (Y) the voltage is raised to about 152v inside the motor and current stays the same while in delta the voltage stays the same and the current is raised to about 77A? how can a 45A controller give more amps then it's rating? I don't get that part...
 

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btw, why is it called a DC motor if inside the motor it's actually AC?

Because you supply DC to the controller.

Look on Wikipedia for more information on this.

how can a 45A controller give more amps then it's rating? I don't get that part...

I would presume it can't. Or, if it can, you are risking it failing.
 

Maxwell

Oct 1, 2016
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About the wiring, shouldn't it be star point to NC, delta point to NO, COM to controller phase wire and the coil + and - to a 48v power source with a switch?

Afaik, the common is just a wire that connects all the end points together. You could hook a neuter upto this but it's not necessary.

The controller (thing that turns DC into 3 phase AC) is just that, something that turns DC into 3p AC, it will be fed with 2 wires, positive pole and negatie pole (3 if you count ground), then from the controller 3 wires will leave, your 3 phases that the controller has created. These will be hooked up to one end of the motor windings. The other end of the motor winding will be daisychained together, thus creating your star point.

In order to switch to delta, you'll need to splice into the daisy chained wire on the other end of the windings, connect those to your NC pole and the INPUT of the relay to another windings star point, do this for all three windings and all three relays (provided you use 3 relays, if you use more you'll need to do more daisychaining), so you essentially create the daisy chained star point again, but this time with an interrupter inbetween.

Then you will have to daisychain your L1, L2 and L3 (3p coming from controller) to the NO contact of the relay. You'll have to match up the phases so each winding gets two different phases (L1 + L2, L2 + L3, L1 + L3), and you'll have to get the phase angle correct or the motor will run backwards (if it does you simply switch out one phase with another and it should correct it).

The two 48V DC connection coming from the battery you will then hook up to the relays coils with a switch of some sort in between, then when you push that switch, you'll go from star to delta.

Current draw will be higher in delta 88v * SQRT3 = 152V * 45A (what your motor can/will draw) = 6.8Kw. As opposed to star configuration; 88v * 45A = 3.9Kw. Alternatively you can see this as, 88v * 45A*SQRT3 = 6.8Kw. You cannot "up" the amperage of the motor as it's simply it's physical limit, however if you switch to delta, the voltage to the windings increases and this the motor will be able to put more power through it's windings, resulting in higher draw from the source, 77 amps to be exact. Essentially what you are doing is lowering the resistance of the motor to pass more power.

I'm really not sure you want to do this... exploding lithium batteries are nasty, and what about the controller, can is handle the extra draw?

Also, concerning the voltage increase in delta; considering your motor is currently hooked up in a star configuration, it's likely that the controller is kicking up the output voltage to the motor, if you hook up a star then line to line Voltage becomes /SQRT3 over the coils, THUS to get 88v over your coils, the controller would have to be putting out 152V line to line, if you then switch to delta, the motor will be receiving 152V, as you've disconnected the "common" (star point) and replaced it with a line voltage on a different phase angle.

It's also possible that your motor is simply "rated" 88v, meaning there is 88v/SQRT3 over the coils or 50v. You need to figure this out before you try this.

Are you sure about the voltage? is it the same with DC motors? btw, why is it called a DC motor if inside the motor it's actually AC?

The laws of physics don't change for different motors :)

It's called a "DC" motor because you feed it DC (but the integrated controller changes that to AC).

The motor can handle that for a short period, it's about 6700 watts but I hope it isn't so with the voltage raise.

It is, if you switch to delta the motor will be receiving 152v, (or 88v depending on what the actual line to line coming from the controller is). I know motors are robust and can handle overvolt for a short while, but there is other components involved as well, the controller for ex, or the battery, it will get smoking hot... you might want to think about thermal management, and maybe overheat protection.

http://www.allaboutcircuits.com/tex...t/chpt-10/three-phase-y-delta-configurations/
http://www.allaboutcircuits.com/tex...t/chpt-10/three-phase-y-delta-configurations/
Quote from that link:
"In balanced “Y” circuits, line voltage is equal to phase voltage times the square root of 3, while line current is equal to phase current. In balanced Δ circuits, line voltage is equal to phase voltage, while line current is equal to phase current times the square root of 3."

Does it mean that in star (Y) the voltage is raised to about 152v inside the motor and current stays the same while in delta the voltage stays the same and the current is raised to about 77A? how can a 45A controller give more amps then it's rating? I don't get that part...

It means that in star the voltage inside the motor will be /SQRT3 or 88v, while the current is (max) 45A, while in delta the voltage is simply supplied to the motor as line voltage (152v) and the current (max) draw will be 77A. The controller will be made to work outside of spec, just like everything else in this setup. The controller is most likely an IC, it will do whatever you tell it to do up to the point you get white smoke.

What i'm trying to tell you, is that what you are doing is not "kosher" and sooner or later you will destroy the E-bike because of this.

The proper way to do this would be with higher spec parts. Get a more powerful motor and extra battery pack, then you can simply have the motor run below spec while in star configuration and at spec when in delta.

You never get something for nothing, if you want more power out of something that isn't rated for it, you'll get more heat, sparks, exponential wear and eventually white smoke.
 
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Maxwell

Oct 1, 2016
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Another something that occurred to me...

Induction motors are frequency controlled, and so they only speed up if you increase the frequency. I'm not sure what you hope to accomplish by increasing the voltage over the coils then?

Anyone have more experience with these types of motors can clarify this?
 

roig12

Oct 29, 2016
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Thanks for the detailed reply, I appreciate it :)

I think you are getting one crucial thing wrong here...
The whole point of switching to delta and not connecting the bike permanently in delta is that for gaining the 70% speed, you LOOSE about 70% torque (it's a fact, I tried riding a bike with a delta switch).
so if I was getting 6.8kw, then I should have crazy torque from 0 speed but that is clearly not the case here.

You said that the voltage is raised to 152v even on a regular star setup (just like it is now), so it means that when the motor is rated for 88v then it actually is rated for 152v meaning that the voltage doesn't really increase but only the amps (which is worst because amps=heat).

It sounds weird to me that the motor will "decide" (by changing to delta) how much current to draw from the amp.
From my experience, the controller has the max amps it can deliver and you can't pull more since it kind of "gives" instead of being "pulled from".
On the other hand, the battery is something that you can "pull" more than it can deliver and then maybe damage it, and also the motor is like that too that you can "shove" more than it can handle.

In the ebike world I see mostly burned motors, sometimes batteries that die but not so much from pulling more than rated current like you would think and very little if any controllers getting hot (more than warm to the touch is rare even).
 

Maxwell

Oct 1, 2016
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Well i'm not entirely clear on how that motor determines it's rotational speed, i just know for a fact that induction motors are speed controlled through frequency of the input, not voltage or current.

The line to line voltage is 152v yes, but the voltage over the windings of the motor is not, it's 88v. If you configure to delta, you are essentially switching the motor windings from series to parallel, meaning they get the full line voltage of 152v.

Nothing in any circuit "decides" how much current it will draw, it will draw as much as it is able to, up to and including a dead short to ground. This is determined by resistance in the circuit. So if you have a low resistance behind a high resistance, that means that the high resistance circuit will have to dissipate the additional power going through it in the form of heat. The controller is not exactly "giving" it's converting from one type of waveform to another, which also means all the power has to go through it, so the more power through it, the hotter it gets.

The controller will conduct as much power as you pull through it.. or until it pops ofc. If you find this hard to believe, then perform this simple test:

Unhook your motor, take the three phases, short them together, turn on the controller.

Going by your experience i'd have to conclude that the controllers are overdimentioned, which is entirely plausible, as electronic components are generally overdimentioned for safety margin. Burning motors seems plausible since you are overvolting them, and the batteries well, i guess it's fine as long as you stay within reason, they will just get pounded harder. Batteries can actually deliver spectacular amounts of current in a dead short so I'd buy that, still none of this can be considered "safe".
 

roig12

Oct 29, 2016
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In the link that I quoted before it said that in star mode it increases the voltage and in delta it increases current.
So if you say that in delta it increases the voltage from 88v to 152v then what about the current? it's the opposite of what that website said.
EDIT: Now that I think about it, ebike controller sellers always write the current of the controller as "limited to XX" which means that they somehow limit the current so what you said wouldn't happen.
BUT, if the voltage is higher, it would cause alot more watts to pass through the controller so it's still in hazard although I don't get how it works because the voltage change happens inside the motor and not inside the controller...
I think I'm gonna end up as a rocket engineer just understanding how motors, amps and voltage changes happen :)

So bottom line, I'm increasing the watts going into the motor thus stressing the whole system...
Well, since my battery is LiPo and can provide even 100A continues and my hub motor weighs 9.1kg and can take about 5.5kw easy (about 7kw possible for short pulls) then the only thing separating me from reliable "delta power" is the controller which luckily is the cheapest part in the system.
Well, I have an 80A controller on the way to me so I guess I will upgrade when it arrives and drop this idea (AND warn my delta using friend who has new relays on the way since he fried the other ones).
 
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Maxwell

Oct 1, 2016
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Current limiting is certainly possible, but then it seems logical to me that there also will not be a performance increase. Like i said, i don't understand how the motor will suddenly "speed up" just because you're increasing the voltage, so until that's clear, i'm not going to be much further help in this regard.

The website is saying the same thing I am, just maybe i'm not wording it the same. This is the sole reason for using 3p power, to decrease the amount of copper required to connect the load. It's also why the voltage is kept high for high power motors, the higher the voltage, the more amps can be sent through a smaller wire.

The conundrum you have with amps VS volts can be solved using ohms law. If you are using 45 amps at 88v then 45*88 = 3960 watts, but if you put 152v into the motor at 45 amps, you get 152*45= 6840 watts. This then means the controller will be delivering 6840 watts to the system instead of 3960 watts, considering the controller is still only getting 88v INPUT, you then get 6840 watts / 88v = 77,73 amps.
 

roig12

Oct 29, 2016
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I really don't get what's going on inside the motor...
I talked with my friend with the delta switch and he told me that he rode the bike for about 3km at high speed with the battery cold, BMS slightly warm, and same for the controller temp.
Sounds weird...
For me, I'm going to stick with a big motor and a big controller along with my LiPo's that can always deliver the goods when it comes to high amps.
Thanks alot for all the great info and help!
 

(*steve*)

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At higher speeds there is a higher back EMF from the motor. This effectively limits rpm to that where the back EMF balances the available applied voltage. If you reconfigure the motor so that the back EMF is lower then the same applied voltage will permit a higher rpm. Even though the stall current may double, the motor is not anywhere near stalled and the current through the motor will not rise to astronomical values.
 
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