42V on 36V system

[erdurbin]

This was briefly mentioned, but no one ever really got back to it.
I have been running an extra 6V 12ah brick in series to my 3x12v 12ah pack.
I really like the higher top end and the torque seems much better. I have to be careful when starting out and only go about 1/4 to 1/2 throttle until I get around 10mph. Otherwise, the amps jump over 30 and is really unnecessary. I am not trying to drag race my bike, I just want a little more help. With this setup, I can achieve easily 17-20mph up a basic hill. Before, I was getting around 12-16mph.

When my pack is fully charged, it is around 46-47 volts. If the amps jump to around 30, I have sometimes seen around a 7-10 volt drop. This is why I try to not give full throttle if I can help it unless I am up to speed.

I will post pics later of my pack. I use a watts up meter to monitor my voltage and amps while riding.

Has anyone else tried this? It does not heat up anything more than my 36V system seems to.

This is just something I have tried temporarily until I get my LiFePO4 pack from Skeuter.

[myelectricbike]

First the applied voltage is being supplied to the motor using PWM (Pulse Width Modulation). Consequently you are applying a constant voltage and current in pulses whose width represent watts. Consequently when you are feeding an excess number of watts to the motor above its rated wattage and the inductive resistance that is in proportion to the actual RPM is exceeded then you get a current spike and a voltage dip due to insufficient inductive resistance to limit current.

(I think that's right but honestly I have not had breakfast or lunch and was working on another project very late last night so its hard for me to actually no what I'm writing until I read it again.) 

[erdurbin]

It was only an experiment. I actually get better long term results with just 36 volts. I get a quick turbo boost for about a mile and then my controller starts cutting out from the voltage sag. Not sure what causes it, but I took my 6 volt off today after it kept cutting out so soon. However, it is pretty nice for a mile. Maybe if I used a dpdt switch as mentioned in another post I could only use it when I wanted to.

[myelectricbike]

My experiment with a 12 volt instead of a 6 volt resulted in shorted phase power leads three times in a row but after the last "upgrade" in wiring I used the 48 volt controller and only had cut outs just before making it back home. I have not upgraded the windings themselves yet by adding a couple of extra strands but that might resolve the problem. I am hesitant to do it because of the polyimide cost. Instead I go very gently on the throttle and jam it only when needed. A motor specifically designed for 48 volts would solve the problem but if I can have 48 volts then I'll probably hold out for 72.

[cadstarsucks]

First the applied voltage is being supplied to the motor using PWM (Pulse Width Modulation). Consequently you are applying a constant voltage and current in pulses whose width represent watts. Consequently when you are feeding an excess number of watts to the motor above its rated wattage and the inductive resistance that is in proportion to the actual RPM is exceeded then you get a current spike and a voltage dip due to insufficient inductive resistance to limit current.

(I think that's right but honestly I have not had breakfast or lunch and was working on another project very late last night so its hard for me to actually no what I'm writing until I read it again.) 

Inductive impedance.  Resistance (R) on the order of 0.5 ohm and inductive impedance (XL) for inductance of perhaps around 1H ( XL=2(PI)FL )

Inductive impedance is called the imaginary portion since it does not actually dissipate power but only stores it.  The resultant impedance is the square root of the sum of the squares or SQRT(0.5^2+XL^2) at an angle of SIN(XL/R). 

In an AC circuit the angle of the impedance has to be included in the current calculation as it will not be in phase with the voltage the way it would be in a resistor.

In an AC motor, the instantaneous current is a bit more complicated since you have the angle and magnitude of the CEMF to remove from the voltage before you can procede to calculate the power lost in the windings.

I had been trying to keep things simple for you ...

Back to the simplified version:  Motor CEMF is directly proportional to motor RPM. 

From the HBS-36 performance curve at no load we have 308RPM and at full load we have 216RPM.  from the ratio of these two numbers we can calculate the amount of voltage developed on the winding resistance for that change in current at the supplied 36V:

winding voltage = 36V - 36V x 216/308 = 10.75V

The no load and full load currents are 1.19A and 20.46A, respectively.  From the difference between these we can calculate the rotor resistance:

rotor resistance = V/(Ifl-Inl) = 10.75/(20.46-1.19) = 0.56 ohms

Dan

[myelectricbike]

Okay, much better. The way to keep things simple is to present one variable at a time, explain it concisely and fully in ordinary terms as you have done here and then move on to the next part of the equation.

It really helps me to think of myself as writing a summary as the way to keep the thing simple and focused. If you do this then even a newbie with no electrical or electronics background who may not understand even the simplest explanation can read and re-read what you have written over time and eventually end up with a complete comprehension using no more than your simple explanation to anchor everything else.

Now on to why 48 volts (or 42 volts under this topic) might be causing phase lead wire insulation to melt,  the controller to cut out or the current to jump while the voltage dips when full throttle is applied to an HBS-36 hub motor.

Good job!   

[mustangman]

   Thanks You Dan, I really understood that formula and the concepts. I like things broke down in simple terms for you can teach me some of your electrical knowlege. I can say now that this forum is improving.

[myelectricbike]

Okay, now in an attempt to address the OP's question, what value is the winding voltage when we apply 42 volts (supply voltage)? And how about the no load and full load currents? What happens to them? Also, what happens to the motor resistance value, does it remain the same when we apply 42 volts to the HBS-36 hub motor?

HBS-36 Design Criteria

Motor

Current

Winding

Supply

RPM

Resistance

No Load

Full Load

Voltage

Voltage

No Load

Full Load

R

Inl

Ifl

Vw

Vs

0.558001492

1.189

20.46

10.75324675

36

308

216

Impedence	Inductive	Motor	Inductive	Angular Velocity
Angle	Impedence	Resistance	Reactance	Radians	Frequency	Henries
XL/R	(R2+XL2).5	R	XL	2n	f	L
4504.063446	2513.274185	0.558001492	2513.274123	6.283185307	400	1
4391.461859	2450.442333	0.558001492	2450.44227	6.283185307	390	1
4278.860273	2387.610482	0.558001492	2387.610417	6.283185307	380	1
4166.258687	2324.778631	0.558001492	2324.778564	6.283185307	370	1
4053.657101	2261.946779	0.558001492	2261.946711	6.283185307	360	1
3941.055515	2199.114928	0.558001492	2199.114858	6.283185307	350	1
3828.453929	2136.283077	0.558001492	2136.283004	6.283185307	340	1
3715.852343	2073.451226	0.558001492	2073.451151	6.283185307	330	1
3603.250756	2010.619376	0.558001492	2010.619298	6.283185307	320	1
3490.64917	1947.787525	0.558001492	1947.787445	6.283185307	310	1
3378.047584	1884.955675	0.558001492	1884.955592	6.283185307	300	1
3265.445998	1822.123825	0.558001492	1822.123739	6.283185307	290	1
3152.844412	1759.291975	0.558001492	1759.291886	6.283185307	280	1
3040.242826	1696.460125	0.558001492	1696.460033	6.283185307	270	1
2927.64124	1633.628275	0.558001492	1633.62818	6.283185307	260	1
2815.039653	1570.796426	0.558001492	1570.796327	6.283185307	250	1
2702.438067	1507.964577	0.558001492	1507.964474	6.283185307	240	1
2589.836481	1445.132728	0.558001492	1445.132621	6.283185307	230	1
2477.234895	1382.30088	0.558001492	1382.300768	6.283185307	220	1
2364.633309	1319.469032	0.558001492	1319.468915	6.283185307	210	1
2252.031723	1256.637185	0.558001492	1256.637061	6.283185307	200	1
2139.430137	1193.805339	0.558001492	1193.805208	6.283185307	190	1
2026.82855	1130.973493	0.558001492	1130.973355	6.283185307	180	1
1914.226964	1068.141648	0.558001492	1068.141502	6.283185307	170	1
1801.625378	1005.309804	0.558001492	1005.309649	6.283185307	160	1
1689.023792	942.4779613	0.558001492	942.4777961	6.283185307	150	1
1576.422206	879.64612	0.558001492	879.645943	6.283185307	140	1
1463.82062	816.8142805	0.558001492	816.8140899	6.283185307	130	1
1351.219034	753.9824433	0.558001492	753.9822369	6.283185307	120	1
1238.617448	691.150609	0.558001492	691.1503838	6.283185307	110	1
1126.015861	628.3187785	0.558001492	628.3185307	6.283185307	100	1
1013.414275	565.486953	0.558001492	565.4866776	6.283185307	90	1
900.8126891	502.6551343	0.558001492	502.6548246	6.283185307	80	1
788.211103	439.8233255	0.558001492	439.8229715	6.283185307	70	1
675.6095168	376.9915314	0.558001492	376.9911184	6.283185307	60	1
563.0079307	314.1597609	0.558001492	314.1592654	6.283185307	50	1
450.4063446	251.3280317	0.558001492	251.3274123	6.283185307	40	1
337.8047584	188.4963851	0.558001492	188.4955592	6.283185307	30	1
225.2031723	125.664945	0.558001492	125.6637061	6.283185307	20	1
112.6015861	62.83433079	0.558001492	62.83185307	6.283185307	10	1
0	0.558001492	0.558001492	0	6.283185307	0	1

[cadstarsucks]

Okay, much better. The way to keep things simple is to present one variable at a time, explain it concisely and fully in ordinary terms as you have done here and then move on to the next part of the equation.

It really helps me to think of myself as writing a summary as the way to keep the thing simple and focused. If you do this then even a newbie with no electrical or electronics background who may not understand even the simplest explanation can read and re-read what you have written over time and eventually end up with a complete comprehension using no more than your simple explanation to anchor everything else.

Now on to why 48 volts (or 42 volts under this topic) might be causing phase lead wire insulation to melt,  the controller to cut out or the current to jump while the voltage dips when full throttle is applied to an HBS-36 hub motor.

Good job!   

The current in an inductor is:

dI=VdT/L

The change in current equals the voltage times the change in time divided by the inductance.  Those with calculus will recognize the little "d" as the notation for the derivative.

This relationship holds true until the inductor saturates.  The inductor saturates when it's core can hold no more magnetic flux, and when this happens the inductance drops to zero.

The motor current is driven by the motor voltage and impeded by the CEMF the series resistance of the winding and the series inductance of the winding.  When the motor core saturates the inductance goes to zero and the motor current is is only limited by the motor resistance, the battery resistance, the wire resistance, and the CEMF so the current skyrockets melting the wires and pulls down the battery voltage through it's resistance.

Dan

[pdonahue]

This was briefly mentioned, but no one ever really got back to it.
I have been running an extra 6V 12ah brick in series to my 3x12v 12ah pack.
I really like the higher top end and the torque seems much better. I have to be careful when starting out and only go about 1/4 to 1/2 throttle until I get around 10mph. Otherwise, the amps jump over 30 and is really unnecessary. I am not trying to drag race my bike, I just want a little more help. With this setup, I can achieve easily 17-20mph up a basic hill. Before, I was getting around 12-16mph.

When my pack is fully charged, it is around 46-47 volts. If the amps jump to around 30, I have sometimes seen around a 7-10 volt drop. This is why I try to not give full throttle if I can help it unless I am up to speed.

I will post pics later of my pack. I use a watts up meter to monitor my voltage and amps while riding.

Has anyone else tried this? It does not heat up anything more than my 36V system seems to.

This is just something I have tried temporarily until I get my LiFePO4 pack from Skeuter.

What size (Ah) are your batteries?  I'm running 48V 10Ah sla and the voltage drop is normally around 5-7 volts, but I've never noticed how high it peaks during startup. 

As for heating up, for the first week that I was running the 48V setup I was checking all the wires frequently because I was fully expecting a meltdown at some point.  The only one that seemed to get even warm was the 18AWG wire coming from my battery (it was an old computer power extension cord that already had the right plug on it).  It would get warm to the touch while riding and that made me a little nervous.  I replaced it with a 14AWG power cord and now there is no noticable temperature increase.

Pete

[cadstarsucks]

Okay, now in an attempt to address the OP's question, what value is the winding voltage when we apply 42 volts (supply voltage)? And how about the no load and full load currents? What happens to them? Also, what happens to the motor resistance value, does it remain the same when we apply 42 volts to the HBS-36 hub motor?

Umm....I was just taking a pot shot at the inductance... reality is a bit more complicated as it is three phase.  That is, however the first time I have seen the actual drive frequencies...interesting that they go to the 400Hz aircraft power frequency...
Dan

[myelectricbike]

...
The current in an inductor is:

dI=VdT/L

The change in current equals the voltage times the change in time divided by the inductance.  Those with calculus will recognize the little "d" as the notation for the derivative.

This relationship holds true until the inductor saturates.  The inductor saturates when it's core can hold no more magnetic flux, and when this happens the inductance drops to zero.

The motor current is driven by the motor voltage and impeded by the CEMF the series resistance of the winding and the series inductance of the winding.  When the motor core saturates the inductance goes to zero and the motor current is is only limited by the motor resistance, the battery resistance, the wire resistance, and the CEMF so the current skyrockets melting the wires and pulls down the battery voltage through it's resistance.
...

Perfect explanation then of what the Watts-Up meter is showing and I assume why cutoff is occurring.

[cadstarsucks]

Perfect explanation then of what the Watts-Up meter is showing and I assume why cutoff is occurring.

I do try... the material sat point varies with temp too so you can expect variance with material batch (impurities), air temp, length and speed of ride, weight of the rider, and grade.

Dan