methods
1 GW
I am just brainstorming out in the open here as I have some spare time.
I have covered this before.
I have two customers asking for a switch (either contactor or mosfet) for overall pack protection.
Details in other threads.
The contactor route is simple. Done deal.
The mosfet route is ... more complicated. It takes test to verify.
Since we are not doing any PWM... we can test in a very basic way.
We have two primary failure modes: Over Voltage and Over Current.
Over voltage results in shorted mosfets
Over current results in overheating
Voltage Test - more on the black magic side
Goal: Induce large transient voltages
To test over voltage we need to understand how a reactive system works.
A 100V battery system will produce voltages in excess of 100V... but most of those are transient... and can be shunted off with large TVS diodes.
For over voltage testing... in reality... one of the best ways to do it on the cheap... is with a representative circuit.
A representative circuit can be built by going to your bike and adding another 10' of power wire between your battery/switch and the controller.
This will increase inductance to a margin point.
Controller selection and onboard capacitance have an impact on this.
The bigger the controller the worse the noise (generally speaking)
To test... charge your battery up to top, top, top - highest voltage you will see... + 10%
Then connect and disconnect the system in the most rude way you can imagine.
* Plug in and out rapidly
* Unplug while under full load
* Plug in with full load applied
Do things that create a BOOST circuit and see where that voltage goes.
You can do it manually... or... I suggest hooking up a gas filled Gigavac contactor and running that either on a uController with a duty cycle... or manually if you must.
Clobber the system until you are confident that you have added enough protection.
Once you are there... REMOVE your protection diodes and CONFIRM that the circuit is destroyed
This is the test for your test and is REQUIRED to know you are actually stressing the system in the way desired.
CURRENT -
This is the part I actually intended to post about.
Our goal is to graph our temperature rise vs continuous current
So... transient load is not all that important for thermal testing. What you really need is to pound your circuit worst case and get an understanding of the temperature rise. This rise is additive to ambient temperature and there will be runaway / failure points.
In the past I have used a 3.5V 100A power supply.
This does the trick for almost all ebike applications.
My favorite used supply is the Sorensen DCS series. These can be had as cheap as $250... and they can be STACKED IN SERIES AND PARALLEL FOR IMPROVED PERFORMANCE.
SO... that is the proper route.
I dont have one of those supplies right now... so what do I do?
Well... What I do have is a 60V 20A power supply, stacks of Lipo, and golf cart controllers.
A standard DC controller can work wonders in a situation like this. Just hook up 50V worth of Lipo, backed up by a supply (to keep things consistent over time), and dont push the controller to its limits.
The controller is expecting to see an inductive load... you will be presenting it with a resistive load... so respect its limitations.
A motor has effectively 0ohms of R... but it has a lot of L... so you see an effectively high IMPEDANCE (Frequency dependent resistance + standard resistance)
You can emulate this by using a power load. IF you hook up a short circuit to the controller... it will smoke nearly instantaneously..
SO... determine first what load you wish to run
Lets say 100A
Determine what voltage you are running... lets say 50V
50V / 100A = 0.5ohms
So... if you were to just apply a 0.5ohm load directly to your lipo you would get your 100A
Easier said than done... but could be done. Just remember that your load will need to be able to handle 5 KILOWATTS
5KW
Not 5 Watts... 5 Killowats
So.. 5 watts will take a chunk of aluminum the size of your pinky finger to 65C (burn you) temp in only seconds.
We are talking about a thousand times that much.
Three orders of magnitude more sorrow
Ok... lets be smart about it.
What if we use 1V and 100A?
Then we only have to deal with 100W
Now we are thinking... and we can approximate this with a 1S10P lipo setup
But... who has this?
Nobody - except someone doing a lot of pack building with big pouches
So here we are looking at the options again.
We ideally want to run 100A continuous at as close to 0V as humanly possible so as to limit power dissipated to only that which is hooked to the mosfets or switch under test.
Will this work with a giant Golf Cart Controller?
Yes - IF YOU CAN ALSO DUMP THE EXTRA 5KW
Which... you probably cant... for any appreciable period of time... So I will leave that to you to discover.
A bucket of water, pump, some steel pipe, and a radiator... you can probably do it with that.
Other than that - good luck... unless you want to do your testing at 20MPH !!
(which... is actually how I would do it if I had to do it TODAY. Any port in a storm while waiting for a supply to ship)
Lightbulbs could work... but you would need kW worth... like a warehouse worth... as they are more like 100ohms when you need half an ohm.
So that was a thought exercise.
Here is how I would make 100A right now:
You buy this for $400
http://www.ebay.com/itm/Sorensen-DC...722754?hash=item23848d8602:g:oRIAAOSwImRYQJsF
Sorensen DCS8-125
1000W, 8V, 125A
Lab Grade CC/CV power supply
Fully programmable
Totally protected
Can create 100A at 0.1V
Exactly what you want.... (er... what I want... so buy it for me for my birthday
)
These supplies work even after smoke shoots out of the back (caps blow off)
They plug into a standard 120V outlet (hence the 1kw limit)
They are tiny and light and just rock all day long
The next step up is 3KW
Those are double thick and triple heavy
They require 240V and you can really get into trouble with them
The 1KW series is plenty dangerous enough to start a fire quick.
The primary failure mode is the fan (which you can hear) which can be serviced and can be replaced or otherwise retrofitted.
In my perfect world... I would own 30 of these supplies.
-methods
I have covered this before.
I have two customers asking for a switch (either contactor or mosfet) for overall pack protection.
Details in other threads.
The contactor route is simple. Done deal.
The mosfet route is ... more complicated. It takes test to verify.
Since we are not doing any PWM... we can test in a very basic way.
We have two primary failure modes: Over Voltage and Over Current.
Over voltage results in shorted mosfets
Over current results in overheating
Voltage Test - more on the black magic side
Goal: Induce large transient voltages
To test over voltage we need to understand how a reactive system works.
A 100V battery system will produce voltages in excess of 100V... but most of those are transient... and can be shunted off with large TVS diodes.
For over voltage testing... in reality... one of the best ways to do it on the cheap... is with a representative circuit.
A representative circuit can be built by going to your bike and adding another 10' of power wire between your battery/switch and the controller.
This will increase inductance to a margin point.
Controller selection and onboard capacitance have an impact on this.
The bigger the controller the worse the noise (generally speaking)
To test... charge your battery up to top, top, top - highest voltage you will see... + 10%
Then connect and disconnect the system in the most rude way you can imagine.
* Plug in and out rapidly
* Unplug while under full load
* Plug in with full load applied
Do things that create a BOOST circuit and see where that voltage goes.
You can do it manually... or... I suggest hooking up a gas filled Gigavac contactor and running that either on a uController with a duty cycle... or manually if you must.
Clobber the system until you are confident that you have added enough protection.
Once you are there... REMOVE your protection diodes and CONFIRM that the circuit is destroyed
This is the test for your test and is REQUIRED to know you are actually stressing the system in the way desired.
CURRENT -
This is the part I actually intended to post about.
Our goal is to graph our temperature rise vs continuous current
So... transient load is not all that important for thermal testing. What you really need is to pound your circuit worst case and get an understanding of the temperature rise. This rise is additive to ambient temperature and there will be runaway / failure points.
In the past I have used a 3.5V 100A power supply.
This does the trick for almost all ebike applications.
My favorite used supply is the Sorensen DCS series. These can be had as cheap as $250... and they can be STACKED IN SERIES AND PARALLEL FOR IMPROVED PERFORMANCE.
SO... that is the proper route.
I dont have one of those supplies right now... so what do I do?
Well... What I do have is a 60V 20A power supply, stacks of Lipo, and golf cart controllers.
A standard DC controller can work wonders in a situation like this. Just hook up 50V worth of Lipo, backed up by a supply (to keep things consistent over time), and dont push the controller to its limits.
The controller is expecting to see an inductive load... you will be presenting it with a resistive load... so respect its limitations.
A motor has effectively 0ohms of R... but it has a lot of L... so you see an effectively high IMPEDANCE (Frequency dependent resistance + standard resistance)
You can emulate this by using a power load. IF you hook up a short circuit to the controller... it will smoke nearly instantaneously..
SO... determine first what load you wish to run
Lets say 100A
Determine what voltage you are running... lets say 50V
50V / 100A = 0.5ohms
So... if you were to just apply a 0.5ohm load directly to your lipo you would get your 100A
Easier said than done... but could be done. Just remember that your load will need to be able to handle 5 KILOWATTS
5KW
Not 5 Watts... 5 Killowats
So.. 5 watts will take a chunk of aluminum the size of your pinky finger to 65C (burn you) temp in only seconds.
We are talking about a thousand times that much.
Three orders of magnitude more sorrow
Ok... lets be smart about it.
What if we use 1V and 100A?
Then we only have to deal with 100W
Now we are thinking... and we can approximate this with a 1S10P lipo setup
But... who has this?
Nobody - except someone doing a lot of pack building with big pouches
So here we are looking at the options again.
We ideally want to run 100A continuous at as close to 0V as humanly possible so as to limit power dissipated to only that which is hooked to the mosfets or switch under test.
Will this work with a giant Golf Cart Controller?
Yes - IF YOU CAN ALSO DUMP THE EXTRA 5KW
Which... you probably cant... for any appreciable period of time... So I will leave that to you to discover.
A bucket of water, pump, some steel pipe, and a radiator... you can probably do it with that.
Other than that - good luck... unless you want to do your testing at 20MPH !!
(which... is actually how I would do it if I had to do it TODAY. Any port in a storm while waiting for a supply to ship)
Lightbulbs could work... but you would need kW worth... like a warehouse worth... as they are more like 100ohms when you need half an ohm.
So that was a thought exercise.
Here is how I would make 100A right now:
You buy this for $400
http://www.ebay.com/itm/Sorensen-DC...722754?hash=item23848d8602:g:oRIAAOSwImRYQJsF
Sorensen DCS8-125
1000W, 8V, 125A
Lab Grade CC/CV power supply
Fully programmable
Totally protected
Can create 100A at 0.1V
Exactly what you want.... (er... what I want... so buy it for me for my birthday
)These supplies work even after smoke shoots out of the back (caps blow off)
They plug into a standard 120V outlet (hence the 1kw limit)
They are tiny and light and just rock all day long
The next step up is 3KW
Those are double thick and triple heavy
They require 240V and you can really get into trouble with them
The 1KW series is plenty dangerous enough to start a fire quick.
The primary failure mode is the fan (which you can hear) which can be serviced and can be replaced or otherwise retrofitted.
In my perfect world... I would own 30 of these supplies.
-methods
