For accessories, a DC to DC converter (such as the Curtis 1410) is used to buck down the 144v (actually higher on peak charge) from the Thunderskys to an isolated 12-14 volt source for accessories such as lights, radios, airhoon, ahem I mean horn etc (which an alternator would otherwise handle in a gas car).
DC-DC converters can also be set up to charge an accessories battery and I’ll probably use a smaller gel-cell (had originally put aside an Optima D36 but weight and space were an issue -and the Optima weighs 25kg!). Although you can get away using the traction pack instead, I prefer a separate accessories battery.
With space running out fast, mounting location is becoming critical, even for the Zivan charger (the next video will be up soon showing the charger mock-up I bodgied together to test available space on the inner wall of the car, which Nathan will cut out, juxtapose to the back seat). Perhaps the DC-DC converter can sit in the opposite cavity.
Breaker to install
Also have to find a place under the hood for the breaker, and other circuit fuses on their own chassis board (charging, heater etc) and this will probably sit next to the controller in an isolated box. Nathan’s getting me some cool lugs and I’ve got some heatshrink tubing to finish off the connections.
The circuit breaker (such as the Airpax brand) is crucial for safety; it must be able to break thousands of amps at high voltage (high-interrupt 10,000A).
Airpax safety breaker
Some folks opt for high power semiconductor fuses, but these can be inconvenient and expensive to replace. I’ll also get a kill pull-knob (so to speak) in the cabin to complement the breaker and make it all road legal. The knob is attached to a cable which in turn can be attached to the breaker switch (there’s a pin-through in the switch) and via suitable levered-mounting that won’t impede surrounding components or put strain on the cable. It has to be able to work under load and when the breaker engages, it’s otherwise mighty hard to throw the switch back manually (and I don’t have the strength anyway).
Space for breaker, and fuse clips ready for assembly
PC switching supply a possibility for DC-DC converter
We’ve also been looking into using PC switchmode power supplies as a possible DC-DC converter -could be a cost saving and other EV’ers have been talking about this for some time now. So long as it can handle the input voltage and be reliable, it could be a good alternative to buying an expensive DC-DC converter from an EV parts supplier.
Experimenting will be interesting (I picked up a couple of ATX supplies in junk piles lately, tested on an old working motherboard (dummy load resistors may have been a wiser choice)), but they work, so cool so far.
You can put DC straight into the AC input but I may bypass the half-bridge rectifier and test straight to the electrolytic side and see what voltage outputs I can get from a 150VDC input…, hah, wish me luck (and don’t try this at home – zap – ouch – if you must try this, do it under supervision!).
Seriously, the trick is to etch a couple of 12+ volt outputs up to a regular 14 volts to effectively handle demand from headlights and properly charge the accessories battery if I install one, and getting suitable amps, and having a stable filtered supply, hmmm… perhaps I’ll start by severing the 5 volt side which is not used (well for PCs, they’re used for sleep mode (I think)) or, perhaps putting a resistor across the positive 5v, and then maybe use a thicker lead for the 12v for better conductivity. Ideally, a circuit re-layout to avoid using 5v would be good and someone here just mentioned that an older AT PSU could be good to work with so I’ll get some info from him on that (mind you, I see less AT supplies on junk piles these days but thankfully I know of a computer salvage stall at the local PC markets – problem here of course is the wattage, typically lower than what I want).
The higher the wattage the better, really (which means be extra careful when fiddling with it); our local computer markets have new ones up to 700W for a good quality PSU. Switchmodes have been known to fail, particularly when manufacturers use components to minimal tolerance (such as electrolytics etc), so going for a good quality supply is crucial if tests work out (and it’s probably time I upgraded my variable bench supply to a higher rated one too).
Power capacitors typically have oil in them which can dry out in cheaper low-tolerance types. In my old CRT fixing days, I’ve seen bulged ones and vented ones with corrosion on the PCB, and SCRs mounted too close to sensitive components due to poor circuit design etc – no wonder there is so much e-junk in landfills when manufacturers purposely build consumer products to have a short lifespan – ah but I’m rambling again. Basically, if you want a PSU to do an important job, buy quality all the time.
Undercharged for my Zivan, but not in the Monetary Sense
On another matter, our supplier sent an incorrect Zivan charger. While identical physically, it delivered less voltage than ideal @around 161 volts (we wanted a higher voltage to charge batteries to maximum potential).
When you order your charger, pay attention to voltage delivery. For example, for a 160Ah Thundersky maximum charge capacity is 4.2 volts which settles to nominal 3.2. To charge all 45 batteries to full efficiency we therefore need 189 volts. Any less and efficiency is impaired. For now we’ve had to charge them individually on a separate supply to get to max voltage – a pain. Now waiting once again for parts; no ‘supplies’ there.
Speaking of efficiency, next thing to do is to check the travel on the accelerator so that we utilize the potentiometer box -> Curtis to the max!
Meanwhile, while I test power supplies, Nathan is wrangling with my ancient Starion wiring and checking continuity etc. Sorting the onboard computers and relays everywhere have been giving us a headache. At least we won’t need the fuel injector computer, but must first make sure it doesn’t handle other functions in the same box. My fat Starion service manual has many wiring diagrams; it’s been very helpful so far.
Stay tuned…
