Kris1 wrote:I didn't realise there was such a tight link between DC supply voltage & Leaf battery voltage Valery;
1) Is there some chargers-for-dummies primers for this technology you could suggest for me to read?
2) With a 415v~ 3 phase version, would the DC peak be 587v after rectification? If so how are you able to charge a Leaf pack with such a high DC source voltage?
In order to understand the below, you need to know that cost reduction and high efficiency were some of our main design criteria for these chargers.
Normally, you would see a standard 2-stage charger topology - an up-converter (aka boost stage) followed by a down-converter (aka buck stage). See more 101 info at http://en.wikipedia.org/wiki/Boost_converter
" onclick="window.open(this.href);return false; (scroll down to related links for info on other topologies). The advantage is truly universal input and output voltage - generally both can range from 0 to close to upper limit on devices used to build these - practically limited to ~450VDC output for standard elcaps and semiconductors. The downside is that you have twice as much hardware, weight, cost, and heat as a single stage unit would have.
Hence our high-power chargers are all single-stage converters. That means that there is now a restriction on the output voltage relation to the input voltage. Boost topology would have a MINIMUM battery voltage = MAXIMUM input voltage you expect. Buck topology would have a MAXIMUM battery voltage = MINIMUM input voltage your expect to see MINUS about 20-30V.
For your practical example of 360VDC input, this means that your output could either be 0-330VDC or 360VDC-450VDC (upper limit can be raised by using different parts inside - we have custom units operating at 900VDC output for some customers...). In reality, the valley between these ranges is even larger due to the likely voltage sag on your source at load. Say, you use a RAV4 battery to charge your Leaf. The battery could easily sag to ~330V from 360V when you load it with 25kW. But it will jump back to 360 if you remove the load. This means that your lower limit on Leaf battery voltage in boost configuration is probably still 360VDC but your upper limit in buck configuration is now 30V lower, or 300VDC.
Unfortunately, this 'valley' covers the bottom 15-20% of Leaf battery SoC. Which means that it would be hard to charge a Leaf from dead zero with a single-stage boost charger off 360VDC input. Obviously, buck is not useful at all as it would not be able to cover any meaningful part of the SoC range for a Leaf pack.
So there are two ways to solve this: 1) go back to dual-stage charger (such as our 12kW SmartCharge units - note half the power of the single-stage - exactly due to the reasons above), or 2) change your input voltage - e.g., by adding an AUX battery to bring the voltage up, etc.
Or, of course, you can just live with the limitation of not being able to charge a completely discharged Leaf.