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[Solved] EV Jerry Can Design+inverter question  

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aez90
(@aez90)
Street cred = 10 mAh
Joined:1 year  ago
Posts: 2
03/07/2018 4:56 pm  

Hi all!

I was looking at building a Jerry Can equivalent for an EV and was hoping you could double-check my logic. I'm in the back-country a lot (so having a safety buffer is nice), and I make one trip semi-frequently with an overnight nowhere near charging (in order to make the round-trip I'd need to add a bit of range during that night). So I figured a battery pack in the trunk that I can pull out and charge from would be nice to have (7.2 kWh should get me what I need).

Here is my design so far:

  • Battery Pack (7S82P~7.2kWh with 3.6V@3500mAh cells)->
  • 7S BMS ->
  • DC step-down 24V to 12V ->
  • 12VDC to 120VAC inverter ->
  • car charger plug that connects to a typical outlet.

Some questions:

  1. I step down 24 VDC because I worried inverters were finnicky about input voltages, whereas the step-down[1] generates nice constant output. Is having constant voltage that important to the inverter?
    1.  If I find an inverter with a voltage input range of say: 21-30VDC before alarms go off[2], would you recommend dropping the step-down from the design or is that too close to the inverter limits for your taste?
  2. Did I do anything glaringly silly in the design phase (I'm sure I'll do something silly when I put it together...but that's for later)? Are there commercial solutions to this I haven't found (the Goal Zero Yeti 3000 is too expensive given I can try DIY).

Thanks for the help!

[1]: Samlex 30A DC-DC

[2]: WRELB 24V Inverter


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aez90
(@aez90)
Street cred = 10 mAh
Joined:1 year  ago
Posts: 2
05/07/2018 6:42 am  

Actually got the answers to my questions - now just waiting on the V2 kits! If a mod wants to take it down feel free, this was a novice question at best - I can't find a delete button of any kind.


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kyletom415
(@kyletom415)
Street cred = 100 mAh
Joined:1 year  ago
Posts: 21
16/07/2018 4:43 am  

Hi Aez90,

Can you clarify what your final design is going to be?

is it: 

  • Battery Pack (7S82P~7.2kWh with 3.6V@3500mAh cells)->
  • 7S BMS ->
  • DC step-down 24V to 12V ->
  • 12VDC to 120VAC inverter ->
  • car charger plug that connects to a typical outlet.

if so, what are your loads going to be? the dc/dc converter can only pump out 30A. that's 360W of power before you use the inverter. assuming it's ~90% efficient, you'll only be able to get about 2.5A (300W) out of your "typical outlet" portion. Will that be enough for your purpose?

 

No idea what you mean as: "Dropping the step down in the design" in 1.1

 

For the WZRELB inverter, it looks like it has a quiescence current draw that looks like it can be kind of annoying. Make sure you have a switch to disconnect it!

 


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