Not completely ready on this but thought I would get the Topic started.
Part 1. Introduction. The Standard Powerbase and the Test Setup.
So now that the building works are complete I've moved into the new study (Laboratory?) and have room to move. Time to get back to work.
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Here's the test setup. A modified Powerbase in the foreground, more on that later. In the background a 30 Amp PSU top right and the electronic load, bottom left.
Electronic load is DC only so it is fed with a Schottky Diode bridge, not very visible but at the end of the Yellow & Green wires, the Black and Red wires go to the load. This bridge is effectively the same as the bridge in the in-car controller, so the voltages measured as the same as the motor electronics will see after rectification.
So how does the Standard Powerbase perform under load?
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Well as we all know not very well.
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Input voltage in this and all the other tests is 13.5 Volts. With a light load (0.1 Amp) this voltage is 12.36 by the time it gets to the electronic load. This is actually fine as there are various known losses along the way. Connecting leads, protection diodes, rectification loss etc. What matters is how many more volts we loose when we increase the load.
So looking at the second column you can see that by the time we get to 3.5 Amps the voltage is down to 5.43 Volts. This is pretty useless so I did not bother increasing the load any further. It's also the reason we have set Overload in PB-Pro to 3.5 Amps. The other problem is that the voltage reduction is not linear, it increases with load. Initially there is a 0.8 Volt change for 0.5 Amp increase in load however there is a 1.5 Volt change at 3.5 Amps.
There are several reasons for the losses, I will go into more detail when I show you the figures for the improved output stage.
The biggest ones are the losses due to RDS on, the resistance of the mosfets. For the ones in the 1.5 Powerbase this is 0.07 Ohm plus 0.175 ohm. These being for the P & N channel mosfets. Total is 0.245 Ohms. So roughly 1/4 Ohm which at 3.5 Amps gives us 0.875 Volts, so significant but not the main culpret as we are loosing a total of 6.93 Volts.
Another smallish contributer are the chokes between the mosfets and the track. If these are removed you get the third column. So another 0.82 Of a Volt. I have removed these for all subsequent tests.
So that's about 1.7 Volts accounted for but still over 5 volts to go. I will explain the other losses when I talk about the new output stage but accept for now that the lions share of this losss is due to the mosfets being poorly driven, both during the switching time and when switched on. This then of course creates a double wammy, increasing lost volts with current and heat.
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So to be continued with a look at a new power stage and some new figures.
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Rich
Part 1. Introduction. The Standard Powerbase and the Test Setup.
So now that the building works are complete I've moved into the new study (Laboratory?) and have room to move. Time to get back to work.
Here's the test setup. A modified Powerbase in the foreground, more on that later. In the background a 30 Amp PSU top right and the electronic load, bottom left.
Electronic load is DC only so it is fed with a Schottky Diode bridge, not very visible but at the end of the Yellow & Green wires, the Black and Red wires go to the load. This bridge is effectively the same as the bridge in the in-car controller, so the voltages measured as the same as the motor electronics will see after rectification.
So how does the Standard Powerbase perform under load?
Well as we all know not very well.
Input voltage in this and all the other tests is 13.5 Volts. With a light load (0.1 Amp) this voltage is 12.36 by the time it gets to the electronic load. This is actually fine as there are various known losses along the way. Connecting leads, protection diodes, rectification loss etc. What matters is how many more volts we loose when we increase the load.
So looking at the second column you can see that by the time we get to 3.5 Amps the voltage is down to 5.43 Volts. This is pretty useless so I did not bother increasing the load any further. It's also the reason we have set Overload in PB-Pro to 3.5 Amps. The other problem is that the voltage reduction is not linear, it increases with load. Initially there is a 0.8 Volt change for 0.5 Amp increase in load however there is a 1.5 Volt change at 3.5 Amps.
There are several reasons for the losses, I will go into more detail when I show you the figures for the improved output stage.
The biggest ones are the losses due to RDS on, the resistance of the mosfets. For the ones in the 1.5 Powerbase this is 0.07 Ohm plus 0.175 ohm. These being for the P & N channel mosfets. Total is 0.245 Ohms. So roughly 1/4 Ohm which at 3.5 Amps gives us 0.875 Volts, so significant but not the main culpret as we are loosing a total of 6.93 Volts.
Another smallish contributer are the chokes between the mosfets and the track. If these are removed you get the third column. So another 0.82 Of a Volt. I have removed these for all subsequent tests.
So that's about 1.7 Volts accounted for but still over 5 volts to go. I will explain the other losses when I talk about the new output stage but accept for now that the lions share of this losss is due to the mosfets being poorly driven, both during the switching time and when switched on. This then of course creates a double wammy, increasing lost volts with current and heat.
So to be continued with a look at a new power stage and some new figures.
Rich
