GoldenMotor.com Forum
General Category => General Discussions => Topic started by: huntley on June 05, 2010, 09:30:16 PM
-
Who42 shows a diagram to build a sensor tester that sounds pretty good. If I could figure out how to paste the figure of it here I would. So I apologize. The point here is that a 9volt battery is used, in series with a 470 ohm resistor to reduce the voltage to 5 volts. Who42 says "The 470ohm resistor and 9v battery combo = 5v was used because it limits the current some what and safer than using 4 AA batteries which would give 6v or 3 AA batteries at 4.5v and capable of to much current." I put one of these testers together last night and I measured 2.08 volts on the far side of the 470 ohm resistor. I measured before the resistor on the resistor lead and have 9.25 v. coming in and I measured the after-resistor voltage on the outgoing lead at 2.08 volts. So I know it's not bad solder points. Why am I not getting a higher voltage reading. Can I use ohm's law someway to figure it out?
-
Hello and welcome.
(http://goldenmotor.com/SMF/index.php?action=dlattach;topic=2114.0;attach=1999;image)
You could replace that 470 ohm with a 4.3 volt 1 watt zener. a This has the exact voltage drop on the battery and will be forgiving under a changing load when the leds switch and allow enough current to your leds
Then Id place a filter cap over the hall input and ground to filter out any noise you could be getting off the zener.
I don't like the circuit really as the led change the load over that resitor when they change from two to one and back again. It creates a pulse noise in the voltage over the resitsor. Those little hall sensors draw only a little amount of current.
Hang for a little and I will make one up.
-
I put one of these testers together last night and I measured 2.08 volts on the far side of the 470 ohm resistor. I measured before the resistor on the resistor lead and have 9.25 v. coming in and I measured the after-resistor voltage on the outgoing lead at 2.08 volts. So I know it's not bad solder points. Why am I not getting a higher voltage reading. Can I use ohm's law someway to figure it out?
The reading is so low because the red led is loading the 470 ohm resistor too much, if you remove the red LED from the circuit, you should find it will work correctly:
(http://goldenmotor.com/SMF/index.php?action=dlattach;topic=1496.0;attach=1320;image)
You could try putting another 1K resistor in series with the red LED if you particularly want to use it as shown below in the modified diagram.
Alan
-
doh I didnt even see red led there there.
Silly me,
-
Thanks, Bikemad. I put the 1K resistor in front of the red led and that upped the reading to 6.62 volts. Is that going to be too much for the hall sensors? Should I try a 470 ohm resistor instead? Thanks
-
Place a amp meter between the ground and resistor and test how much currnet goes through the resistor and adjust resistor to meet led spec.
If your led draws like my test led. 50ma
You want at least a 6v drop at 50ma so you need .5 resistor.
You want 9v/.050A=180 ohm
2v led at .050A, a 40 ohm on.
180-40=140
as close to 140 ohm. But it must go on the 9v terminal not the 470 ohm.
-
Ok I am building a E-bike lab box from parts that any enthusiast should be able to get their hand on.
At the heart of this box I have 2X15va power transformers that will be limited to 1 amp each. They have good isolation at 30v.
So here is the plan.
It will be a cell charger up to 29.4v with a home made BMS. It will have a hall tester and throttle tester. I and I am going to install a inductance meter as well to test the windings.
-
Here is a led on a 9v battery. This is a nimh rechargable and needs a bit of Juice.
The resistor is two 70 ohm 1/4 watt in series. .5 watt 140 ohms. total.
The led would prolly go dark when the battery was flat too.
I want my lab to have the right stuff in it, Some help with some new designs would be great.
-
The resistor is two 70 ohm 1/4 watt in series. .5 watt 140 ohms. total.
Sorry amigo. Each resistor sees the total current, so it's 1/4 watt, 140 ohms total.
-Dave
-
The resistor is two 70 ohm 1/4 watt in series. .5 watt 140 ohms. total.
Sorry amigo. Each resistor sees the total current, so it's 1/4 watt, 140 ohms total.
Dave, I think you'll find that Leslie is 100% correct in this instance.
If a single resistor can handle 0.25 Watts, two resistors in series will handle a total of 0.5 Watts (0.25 Watts each).
Although the Current is the same in both resistors, the Voltage across each resistor is not, it's only half the total voltage.
Try and think of it in terms of light bulbs, where the filaments are basically simple wire resistors enclosed in a gas filled glass container, and it might be easier to understand:
- A 12V source powering a single 12V 10 Watt bulb will have a current draw of ~0.83 Amp. (Watts = Volts x Amps)
- A 12V source powering two 6V 5 Watt bulbs in series will also have a current draw of ~0.83 Amp.
The Current and the total Wattage remains the same, but the actual Voltage across each bulb is reduced by half to just 6V.
Although I'm not very good at explaining how and why, I do know that Leslie is right, and I'm hoping that you will be able to see this too.
If you're still not convinced, try some simple calculations using the formulas (formulae) below and check your results.
Alan
-
I was calculating the heat watts needed to burn 6v 50ma, I figured I used 2 series 70 ohm 1/4 watt resistors each would divide the voltage drop into 2, 3v each resistor. So 3vX0.05A = .15 watts. For both resistors that would be .3 watts so I said a half watt resistor as this is standard and its good to give yourself a 3/2 overhead ratio with the .5 watt series divider,
Anyway,
We need to rectify the AC power transformers. Note I have not removed the original 220v AC connection so all I am playing with as it seems 15vdc at one amp. For each of these.
This tranformer is a multi-cenret-tap 15va transformer. I am going to use the neutral phase push for a positve DC rail and the active phase push for a positive DC rail and the center tap for ground.
(http://images.books24x7.com/bookimages/id_8976/fig441_01.jpg)
The first two are half wave rectifiers, the first is with no center tap, one and the other, like mine with a centre tap. The third is a full wave recifier. It uses a trick where you can gain rail output by rectifying both push and pull phases of both neutral and active of the AC output of the transformer..
half wave rectifier
I used some IN5404 recifier diodes to convert the AC into DC wave form. Doing like this onto the transformer means I wont need to install diodes to any device I choose to us on it.
There are some different ways to mac the AC into DC. This half wave rectifier is very basic and keeps the volts per one amp VCA close to the rail voltage.
The Black wire will be ground, and the the end points of the diodes will be the output.
Edit sorry for the wrong process.
-
If you're still not convinced, try some simple calculations using the formulas (formulae) below and check your results.
Alan
How I came up with the formula is based on Ohms law like you say.
V/I=R
So I saw his voltage over that diode and it was the led. 2v Is close enough,
If it was a 50 ma led we need 50ma to pass any resistor.
Lets find the resistance of 9v @.05A . 9v/.05a=180 ohms.
We can not exceed 180 ohms in our circuit.
Lets find the resistance of the Led switched on.
2v@.05a 2v/.05a = 40 ohms.
Now we need to calculate the left over resistance from the 180 ohm.
180-40 = 140ohm
When in series with the led .05 amps is allowed to pass at 9v.
Now we need to calculate the wattage resitor.
P=VdXI
P= watts
Vd= voltage drop.
I= current
Voltage 1 (9v) minus voltage 2 (2v led)
V1-V2 9-2=8v
Vd= voltage drop= 8v*.05a = .04 watts
Use a 140 ohm, 1 watt but I found .5 fine.
-
We build a new hall sensor tester out of this supply voltage and much more. We can soon use some IC's to regulate the current and voltage properly.
These two transformers are wired in series with a half wave rectifier on each series output with no filter (capacitor) yet. They will be able to run paralell up to 15v at 2 amps or series 30v 1 amp charging station for both SLA Lifepo, Lipo, Lets put a single cell charge abilty in there too and a soild 1 to 2 amp constant current supply.
We have a good 40 VDC 50% swfm 50hz rail voltage.
Those 2 transformers both tested 20.02 and 20.01v, so no presence of isolation problems here.
-
My transformer is now charging an SLA battery. I used a 2,200uf cap to filter out the rectified DC current clean and use a LM317t in constant current mode.
(http://goldenmotor.com/SMF/index.php?action=dlattach;topic=2226.0;attach=2491;image)
In this pic I use a 1.5 ohm resistor and this regulates to .83a.
(http://www.reuk.co.uk/OtherImages/lm317t-current-regulation-circuit.gif)
Lm317t current formula
1.25v/I
1.25v/1a= 1.25 ohms
I then bump up the resistnace to 1.22 ohms.
(http://goldenmotor.com/SMF/index.php?action=dlattach;topic=2226.0;attach=2489;image)
Perrrrfect.
This will hold one amp over any voltage under 15v or very close. I need it to be spot on.
I just need to see at 15v and still draw 1 amp.
Then configure a switch so when the battery reaches 15v it switches to another regulator 13.76 @ 1 amp.
-
SLA is at 13.33v at a rock solid 1.00 amp supply.
-
13.55 @ 1 amp.
The Lm317t sink needs to be a little bigger as its getting hot to touch. As the voltage gets higher on the battery this wasted wattage should lower by about 2 watts.
The transfromer is warm to touch,
We can do some Lm317t heatsink calculations tomorrow to pick the best option for a heat sink.
This would be perfect 1 amp constant current charging station for test charging 4 Lifepo4 cells.
-
Finished charging the 24ah SLA. from 12.55v cold to 15v hot.
Holding 15.00v and still a rock solid 1 amp.
(http://goldenmotor.com/SMF/index.php?action=dlattach;topic=2226.0;attach=2499;image)
-
Ok I want to make this more efficient. We are loosing a lot of wattage in the initial stages of the charge.
But we can start working on our hall effect etser and stuff now.
Im am going to use another linear regulator called an LM7805 or if I regulate the voltage closer to 5v with a resistor A LM78L05 Should be fine.
http://www.national.com/ds/LM/LM78L05.pdf (http://www.national.com/ds/LM/LM78L05.pdf)
(http://icas.to/sdr/sr_lite_ii/01_ps_files/lm78l05_to92_pkg.gif)
(http://circuits.datasheetdir.com/39/LM78L05-circuits.jpg)
As you can see the regulator is very simple and easy to configure for the power supply.
I will offer up a better circuit design pics soon.
I am going to try can use the ground referance point on three of these LM78l05 to to switch the leds off and on.
The ground pin requires smaller than 10ma to regulate a 5v signal so we can kno we are not overloading the hall sensors to run the leds..
-
Here is a preview of the newer circuit, I need to test out.
Maybe stick some 100 ohm variable pot resitors on the hall output wires to calibrate the off voltage to 0v. We will see soon.
(http://goldenmotor.com/SMF/index.php?action=dlattach;topic=2226.0;attach=2501;image)
This should be able to run forever off the halls and create very little load on the hall sensors.
The lights will switch on when ahll sensor is on. and the LM7805 should not need to draw any huge am,ount of current to switch on.
I need to learn how much current actually negates the led to switch off.
The power supply.
The circuit provides 9v to the entire circuit, the hall senors are rated 5v @ 7ma.
We are running three sensors so we will need to burn off 4v @ .021 amps.
9v @ .021a Circuit = 428 ohms.
We can not exceed 428 ohms in this sub circuit.
3 hall sensors in parallel rated at 5v draws .021 amps
hall R= 5v/.021a = 238 ohm
Calculate the divider.
428 ohms - 138 ohms = 290 ohms.
290 ohm 1/4 watt for load regulation to the hall sensor.
The lamps..
With 140 ohm resitor when the hall supply is opend through the output on the ground pin it provides 3.8v to this ground pin causing the the output volats of the lm780-5 to swing + 5v to 3.8v 8.8v
The 140 ohm resistor needs to be enough to allow 50ma of cirrent through at 8.8v. So 136 ohm is perfect
When the hall sensor closes to ground 0v it causes the ground to regulate the LM78L05 to 5v and the resistance of the whole circiut should be 180 ohms at 5v. And should only allow .027 amps to flow this led should drop to almost on at 1.1v and switch off.
The load of the leds should have no effect on the input of the hall in anmy case there is no reason you can not filter it
..
So we put this circuit away and play with it soon and work on a throttle tester as I wait for some funds to get the regulators and test this out.
-
I just bought some parts to build this circuit.
I just lost the parts to build this circiut.
::) ::) ::) ::)
(http://goldenmotor.com/SMF/index.php?action=dlattach;topic=2226.0;attach=2503;image)
The smallest Led I could get was in the 20ma range which is the absolut max that a hall can pass.
I still think for a lab tester I don't want to be stressing the parts inside the motor. Because of how much work the halls take to replace.
Im still going with the regulator ground pins to do my switching.
Here it is simulated as best as I could manage.
(http://goldenmotor.com/SMF/index.php?action=dlattach;topic=2226.0;attach=2505;image)
-
Why not just use some driver transistors triggered by the hall sensors to drive the leds? Then you can skip the 7809 and the resistor, and use only one 78L05. (which are rated for 100mA; enough for all 3 leds...)
-
The LM7805 uses a reference voltage to regulate the volatge.
I am using the ground pin and it only needs if that 10ma, I think the transitors unless they are Fet have to use too much resistance on the base to switch it on.
Can you suggest a part that can switch a 5v 20ma source from the base to emitter with under 10ma base current? no fets as this may require a biase.
Oh I get it,
Maybe I could get the voltage to 2.5 v as far as the transistor can go down in volts and have it almost on at the base. Then whe the hall fires some current it opens the BCE to open and we have a light.
Correct?
-
Like this.
(http://goldenmotor.com/SMF/index.php?action=dlattach;topic=2226.0;attach=2508;image)
-
The MPSA13 looks like it will work,
(http://letsmakerobots.com/files/userpics/u1533/IR_obstacle_detector_2_Schematic.jpg)
I found this very simple IR detector circuit that almost looks the part.
Will this transistor do the trick?
-
Ok I got this MPSA14 transistor going. Its pretty sensitive with A hFE of 5000 at 5v 10ma
(http://goldenmotor.com/SMF/index.php?action=dlattach;topic=2226.0;attach=2511;image)
Originally I want this circuit to run installed on the bike too. I can see this happening still.
Base on voltage meets our requirements @ 2v nd this darlington pair transitor has a hair trigger,
I can get it to switch on at 2v 2ma.
I have got all the current going around the circuit pretty efficiently. It a little hot up the top but you need to cut some watts out somewhere.
Now to draw it up,
I am pretty sure my last circuit using the LM7805s for amplifiers worked in my humble opinion. But I will conceed this design is better again.
If you look the led is drawing 2v @ 20ma the base to trigger is only 2.5ma and is set at 2v,
You can save a heap of base current placing a resistor beteen gnd and emitter .
The switch simulates the hall switching at the base leg causing the transitor to switch on and off.
-
Here is the 5v version.
(http://goldenmotor.com/SMF/index.php?action=dlattach;topic=2226.0;attach=2513;image)
-
Seems like you're on the right track here... ;) Most general purpose small signal transistors can deliver around 100mA and they only need 0,7V to open the CE...
Now, I haven't practiced this theory since school 20-25 years back, so it's only form memory my suggestion... ;)
-
Seems like you're on the right track here... ;) Most general purpose small signal transistors can deliver around 100mA and they only need 0,7V to open the CE...
Now, I haven't practiced this theory since school 20-25 years back, so it's only form memory my suggestion... ;)
Same here I did electronics engineering 25 years ago and didnt even use any of it till I got an ebike.
The simulation proggy helps a lot.
I wanted something that had low volts and current on the base and the simulation transistor seemed to started switching on at .7 and full on properly between 1.8v and 2v just like the spec sheet says.
I saw one circuit with darlington pairs trigger from the current off you fingers. EG touch sensitive.. I got a grip on the math for the transistors but I need to familiarise myself with how it works or else I am wasting my time.
If you were to ask me ohms law, LOL I couldnt tell you, I have to look at each calculation I am making and make it up. The Law helps you to understand how the processes of the math works in the science. But if the penny doesnt drop, attempting to apply the math is a trivial pursuit. If I wasnt to understand how it works I woukldnt even know what Law goes where.
Its 2am here and I am getting tired. More of this latter,
Thanks for the suggestions. I am determined to make this proper
Sooner or later I would have to deal with the transistor formula again. I was trying to avoid it.
I am waiting to get the bills together for a Magic Pie and just building things while I wait.
I will be looking at building a BMS for some cells I have comming and using that 1 amp transformers ive been playing with..
Again I was going to use the LM338 almost identical to the LM317t but 5a rateing for each cell but this is overkill compared to some small transistors. But the current and voltage regulation on a cell would be spot on.
I had a simulation BMS built just using resistors and its fine at 1 amp. Something about using 10% of your charge for balancing.
Last but not least I have some LM2576 simple switchers ICs good for 60v I am itching to put right up at the rectifier. And on a solar panel charger I am working on.
The four panels in series reads over 80v and can output 80 watts at 68v and I plan to use 18 lifepo4 cells on the trailer jump battery. 59.4v cold and 64.4v hot. And for my main bike pack I want 16 cells.
The solar jump pack will be a 1.2 amp charger to the other pack. This will allow the current always travel down hill to my bike pack.
Anyway thanks again.
Good night all. I needs some sleep.
-
If you're looking for efficient voltage regulators, take a look at the MC34063... It exist in most car mobile phone chargers and can handle up to 1.5A by itself. It's a dc-dc converter in an dip-8 package, and can regulate both up and down...
Who hasn't some 12V mobile phone chargers laying around? ;)
http://www.st.com/stonline/products/literature/ds/5257/mc34063eb.pdf (http://www.st.com/stonline/products/literature/ds/5257/mc34063eb.pdf)
-
That 8 pin pack would be great as a sub circuit switcher.
-
Ok I got a good one here that is tested in solid state. It was easier than I thought.
I used the MPSA14 as they are 20c a pop and used some harder shut off at the base snd biased it above the led resistors on the drain legs
I works extremely as a thorttle tester as well and the led have a good contrast of brightness on the twist.
I need to add two more channels of leds
All channels tested well
I will provide more soon.
-
Sorry the first image has my Led the wrong way and why have all that gain the darlington paired MPSA14 has if your not using it.
By placing 13k diodes I recced the current load over the hall. In essence now this should have no impedance issue if one decides to use this circuit all the time installed.
The output voltage of the throttle unconnected reads .71v connected so this should look after the .6v failure beep codes with the MC, and reaches full twist to 3.2v connected. I'll take it for a test ride using this as a throttle amplifier system and see if it needs more resistance between the base leg and ground
(http://goldenmotor.com/SMF/index.php?action=dlattach;topic=2226.0;attach=2533;image)
The MPSA14 is used as a high gain amplifier NPN transistor. Using such a device allow one to trigger lights or even a motor with the smallest of base current.
Yesterday I had a mosfet driving a motor and I was using the current passing through my fingers to conttroll the speed. The tighter I would grab the gate wire and positive the faster the motor would go.
Similarly I had one of these MPSA14's switching slowly on and off by just touching the base wire alone. It amplified everything quite a bit.
(http://goldenmotor.com/SMF/index.php?action=dlattach;topic=2226.0;attach=2535;image)