Few entry level PHEV questions.

[Dan.]

The original title was: "What my physics book didn't teach me". For I while I thought surely I was presented this material in Physics 208, but somehow just skated through on temporary memory anagrams. Went back to the text and I really didn't get most of this stuff covered in coursework, so I guess that's what I get for going software and not hardware.

Anyway, here are a few questions I've been mulling over. Green for answered (I think) Red for unanswered yet.
UPDATE: I've got answers included inline. I've added some questions as well.

• What's Hall sensor - Well Wikipedia set me strait. Any wire with a current will spit out a very predictable EMF. By measuring the EMF you can deduce (very accurately) the current in the wire. What makes them cool is that they are non-invasive.
• What's a Coulomb Counter - I'm beginning to think it's a Hall Sensor with a watch. Current (which is what the Hall sensor measures). A Coulomb is a unit of charge defined (recursively) as the amount of charge that passes through a wire in one second if that wire has a constant current of 1 Amp. So it's basically one Amp Second. So 3600 Coulombs is one Amp Hour.
• What unit is abbreviated "CA" - When I look at battery specs they often show charge and discharge specs and they very depending on something called "CA" (not California). Well at first I thought "C" was Coulomb since that is what my silly Physics book said, but Wikipedia said that C in this context C is a "current".. ie Amps. More over, 1C is the current that will drain your batter in exactly 1 hour. So for a 40Ah battery, 1C is 40Amps. Nutty. So maybe that is what C is, but what the hell is CA? Is C just a constant so CA is basically "C many Amps"? Damn screwy notation if you ask me. Just giving Amps seems to make more since. Only logic would be if C changes as your battery capacity changes so that they could linearize the equation. So it's more like C(x) Amps.

  Originally Posted by ken1784

  I think "C" stands for capacity.
  With the 40Ah capacity battery, you are correct that the 1C charge is 40A, 2C charge is 80A, 0.5C charge is 20A and so on.

  Originally Posted by krousdb

  Ken is correct about CA. It is a standard unit ued by battery manufacturers when referring to charge or discharge rate. This is because they make batteries with varying capacities. It is easier to publish charge and discharge curves using CA because the same curve would apply to all battery sizes. a 40AN battery with a max discharge rate of 3CA would be capable of 120A discharge rate.

• How, in terms of Ohms Law, does regen work - As best I can guess, Regen raises the voltage past 240V. So basically at the moment of regen, you have the MG on the bus at some voltage, say 300V, and you have the Traction battery on the bus at say 200V. So now it's analogous to two batteries (one 300V one 200V) in parallel. Is it true that two deltaVs in parallel will equalize? So since the MG is at a higher potential, the coulombs flow to from the MG to the pack.

  Originally Posted by ken1784

  There is approx 0.35 ohm internal resistance on the Prius 215V nominal voltage pack.
  When it is charged by 100A current, the voltage increment is 0.35ohm X 100A = 35V (Ohms Law), then the battery voltage becomes 215V+35V=250V.

  So the when a higher voltage is on the same "bus" as the battery, the battery is charged.

• How, in terms of Ohms Law, does assist work - As best I can guess, when the MG want juice they close a circuit from the pack to ground. That opens the flood gates through the motors, but how does an electric motor choose how many amps to draw. Does it vary it's resistance to throttle the AMP draw? If not how else can it do this? If it does "go to ground" then isn't all that manufactured resistance just turning into heat? From what I'm reading on synchronous AC Motors, this point is just kinda accepted as a given. Perhaps this is part of the "magic" of the inverter.

  Originally Posted by ken1784

  When it is discharged by 100A current, the battery voltage becomes 215V-35V=180V.

  Originally Posted by krousdb

  To answer your question about work, you are correct that the magic is in the inverter. The inverter is a variable speed motor controller, outputting the sine wave at a desired frequency. The motor will turn at a rate dictated by the output frequency.

  So the when a lower voltage is on the same "bus" as the battery, the battery is discharged. The inverter supplies that "lower voltage" on the bus, this is how it gets it's juice to do it's work.

• Are Voltmeters spec'd for a maximum deltaV? - I'm just curious about the danger of touching the high volt leads with a little voltmeter. How does that not blow the volt meter and ensue general havoc. Seams closing a curcuit across a high deltaV would be inherently dangerous, even if that curcuit was a voltmeter.
• How do you serially wire up 16 3.2V batteries safely? - I'm thinking the first few would be ok, but as you added each new battery to the chain isn't the voltage your dealing with getting higher and higher. Seems the batteries in a PHEV kit are always "hot" or "live". Any other precautions.

Like I said, silly questions, but for the life of me they weren't covered "directly" in Physics 208.

11011011

[fuzzy1]

• What unit is abbreviated "CA"

CA - Cranking Amps. Measured at a warmer temperature than CCA, Cold Cranking Amps, a winter spec.

The others are more complex that I can describe now. Explanations require more than Ohm's Law, and currents are deliberately controlled by the car's brains.

[ken1784]

Originally Posted by Dan.

What unit is abbreviated "CA"

I think "C" stands for capacity.
With the 40Ah capacity battery, you are correct that the 1C charge is 40A, 2C charge is 80A, 0.5C charge is 20A and so on.
I have never seen the "CA" unit. Maybe, someone creates the very local "CA" unit by himself.

How, in terms of Ohms Law, does regen work

There is approx 0.35 ohm internal resistance on the Prius 215V nominal voltage pack.
When it is charged by 100A current, the voltage increment is 0.35ohm X 100A = 35V (Ohms Law), then the battery voltage becomes 215V+35V=250V.
When it is discharged by 100A current, the battery voltage becomes 215V-35V=180V.

How, in terms of Ohms Law, does assist work

I have no clue what your question is.

Ken@Japan

[krousdb]

Originally Posted by Dan.

The original title was: "What my physics book didn't teach me". For I while I thought surely I was presented this material in Physics 208, but somehow just skated through on temporary memory anagrams. Went back to the text and I really didn't get most of this stuff covered in coursework, so I guess that's what I get for going software and not hardware.


Anyway, here are a few questions I've been mulling over. Green for answered (I think) Red for unanswered yet.

• What's Hall sensor - Well Wikipedia set me strait. Any wire with a current will spit out a very predictable EMF. By measuring the EMF you can deduce (very accurately) the current in the wire. What makes them cool is that they are non-invasive.
• What's a Coulomb Counter - I'm beginning to think it's a Hall Sensor with a watch. Current (which is what the Hall sensor measures). A Coulomb is a unit of charge defined (recursively) as the amount of charge that passes through a wire in one second if that wire has a constant current of 1 Amp. So it's basically one Amp Second. So 3600 Coulombs is one Amp Hour.
• What unit is abbreviated "CA" - When I look at battery specs they often show charge and discharge specs and they very depending on something called "CA" (not California). Well at first I thought "C" was Coulomb since that is what my silly Physics book said, but Wikipedia said that C in this context C is a "current".. ie Amps. More over, 1C is the current that will drain your batter in exactly 1 hour. So for a 40Ah battery, 1C is 40Amps. Nutty. So maybe that is what C is, but what the hell is CA? Is C just a constant so CA is basically "C many Amps"? Damn screwy notation if you ask me. Just giving Amps seems to make more since. Only logic would be if C changes as your battery capacity changes so that they could linearize the equation. So it's more like C(x) Amps.
• How, in terms of Ohms Law, does regen work - As best I can guess, Regen raises the voltage past 240V. So basically at the moment of regen, you have the MG on the bus at some voltage, say 300V, and you have the Traction battery on the bus at say 200V. So now it's analogous to two batteries (one 300V one 200V) in parallel. Is it true that two deltaVs in parallel will equalize? So since the MG is at a higher potential, the coulombs flow to from the MG to the pack.
• How, in terms of Ohms Law, does assist work - As best I can guess, when the MG want juice they close a circuit from the pack to ground. That opens the flood gates through the motors, but how does an electric motor choose how many amps to draw. Does it vary it's resistance to throttle the AMP draw? If not how else can it do this? If it does "go to ground" then isn't all that manufactured resistance just turning into heat? From what I'm reading on synchronous AC Motors, this point is just kinda accepted as a given. Perhaps this is part of the "magic" of the inverter.

Like I said, silly questions, but for the life of me they weren't covered "directly" in Physics 208.

11011011

Dan,
Ken is correct about CA. It is a standard unit ued by battery manufacturers when referring to charge or discharge rate. This is because they make batteries with varying capacities. It is easier to publish charge and discharge curves using CA because the same curve would apply to all battery sizes. a 40AN battery with a max discharge rate of 3CA would be capable of 120A discharge rate.

To answer your question about work, you are correct that the magic is in the inverter. The inverter is a variable speed motor controller, outputting the sine wave at a desired frequency. The motor will turn at a rate dictated by the output frequency.

[fuzzy1]

For automobile starting batteries only, I'm sticking with CA being Cranking Amps, and it is measured at 32F. CCA is measured at 0F. Here is a reference.

[Dan.]

Thanks Dan & Ken. Good stuff, I think I beginning to get my head around this subject. A few more questions that came to me later (I put them in the OP too).

Originally Posted by Dan.

UPDATE: I've got answers included inline. I've added some questions as well.

• Are Voltmeters spec'd for a maximum deltaV? - I'm just curious about the danger of touching the high volt leads with a little voltmeter. How does that not blow the volt meter and ensue general havoc. Seams closing a curcuit across a high deltaV would be inherently dangerous, even if that curcuit was a voltmeter.
• How do you serially wire up 16 3.2V batteries safely? - I'm thinking the first few would be ok, but as you added each new battery to the chain isn't the voltage your dealing with getting higher and higher. Seems the batteries in a PHEV kit are always "hot" or "live". Any other precautions.

11011011

[Dan.]

Originally Posted by fuzzy1

For automobile starting batteries only, I'm sticking with CA being Cranking Amps, and it is measured at 32F. CCA is measured at 0F. Here is a reference.

Sorry but I think Ken and Dan got the Prize. Sometimes CA does mean Cranking Amps, and CCA does mean Cold Cranking Amps. But when your reading a LiFe battery spec, CA means "Capacity" as Ken pointed out, or perhaps a better term would be "Capacity based Amperage". I hate it when scientific terms get overloaded, but what's done is done.

11011011

[ken1784]

Originally Posted by Dan.

So the when a higher voltage is on the same "bus" as the battery, the battery is charged.

Correct.
Please be careful when you connect the 300V and 200V battery together.
Assuming the both batteries have the same 0.35 ohm internal resistance, the charge current will be 100V / (0.35+0.35) ohm = 143A.
That's huge!

Are Voltmeters spec'd for a maximum deltaV?
How do you serially wire up 16 3.2V batteries safely?

Please be aware that "ALWAYS wear high-voltage insulated gloves when diagnosing the Hybrid System."
http://www.autoshop101.com/forms/Hybrid15.pdf

Ken@Japan

[Dan.]

Originally Posted by ken1784

Correct.
Please be careful when you connect the 300V and 200V battery together.
Assuming the both batteries have the same 0.35 ohm internal resistance, the charge current will be 100V / (0.35+0.35) ohm = 143A.
That's huge!
Please be aware that "ALWAYS wear high-voltage insulated gloves when diagnosing the Hybrid System."
http://www.autoshop101.com/forms/Hybrid15.pdf

Ken@Japan

http://tinyurl.com/googleProducts00002-03200-M

Yikes, $100 gloves. The price of my Enginer Kit just went up 5%.

Understood on the warning. Thanks for the link.

11011011

[ken1784]

You can buy insulated gloves at $100.
You can not buy your life at any price.

Ken@Japan