Aerowhatt
Gold Member
Posts: 411
Joined: Wed Jan 28, 2015 1:52 pm

Re: Using the battery as an emergency supply

Sat Jun 10, 2017 5:20 am

9h1bw wrote:Thank you both for your replies. Which mirror each other.

Thus my idea is a non starter.

Thank you for your help.


I disagree! You just need to go about it differently. With one more 12 volt (deep cycle) battery, a backup system using the car works quite well. By running a small load over along period of time one wastes nearly 500 watts/hr running the cars systems in ready mode. So a small load is dwarfed by the (overhead) waste. The key is to power the small load from a deep cycle battery external to the car. If you are using an inverter to power the load you can use the audible alarm on the inverter as your reminder to put the car in ready mode for a while and recharge the deep cycle battery.

Using canion and testing this out, a low (alarm sounding but inverter still powering load) deep cycle 12v 100ah battery will charge from the DC to DC (to 80%) at around 1,100 watts which works out to a bit less than 65% overall efficiency. Sounds pathetic efficiency wise but think about it compared to a gas generator which would be more like 15% with engine efficiency factored in. Besides while efficiency is important, it's importance is far from the most important factor in emergency back up power.

Lets say your ham radio needs 100 watts/hr (Chosen arbitrarily). The external deep cycle battery could run it for 5 hours between (and during) 45 minute high amperage recharges. Running the external deep cycle battery between about 30% SOC and 80% SOC gives best efficiency for the entire system. So the car is only connected to and charging the external deep cycle less than an hour out of each 6 hours of run time for the radio.

A fully charged traction battery could run such a load for several days using this strategy!

Aerowhatt
2014 cool silver ES, acquired new 4/2015
2014 Labrador Black Pearl ES, acquired new 3/2016

kiev
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Location: The Heart o' Dixie
Contact: Website

Re: Using the battery as an emergency supply

Sat Jun 10, 2017 5:42 am

How are you charging using solar--is it direct DC from the panels or do you have battery storage...?

As far as less expensive options, variable frequency motor drives, VFD's, are quite plentiful from surplus and auction sites. i have used one with dc connected directly to the dc buss bars to drive a 3-phase motor. You would want a reactor on the output and could use a 3-phase transformer with only 2 legs connected to provide that filtering plus generate a single phase 240vac at 50 Hz. You don't need the chademo connector, just use 2 large terminal socket lugs for the DC and a small jumper wire to control the relay.
kiev = kenny's innovative electric vehicle

9h1bw
Posts: 27
Joined: Sun Mar 19, 2017 2:35 am

Re: Using the battery as an emergency supply

Sat Jun 10, 2017 6:04 am

Aerowhatt,

Now the solutions are coming in fast. Thank you for you suggesting to charge a deep cycle battery using the high power dc to dc converter of the iMiev. From your figures it is much more efficient, even though the auxiliaries consume 500w/hr. (So this is the reason the fuel gauge depleates when stuck in traffic and at a standstill).
Do you know what is the transfer rate of the iMiev dc to dc converter?

BTW what does SOC stand for ?

This solution is cheaper than using a dc to ac converter.

Thank you all for you valuable help.

9h1bw
Posts: 27
Joined: Sun Mar 19, 2017 2:35 am

Re: Using the battery as an emergency supply

Sat Jun 10, 2017 6:22 am

Kiev,

I installed a domestic 1840wp grid solar panels tied to the utility supplier. I export all unconsumed generated power to the grid and import from the grid when consumption exceeds generated and at night. On average I generate what I consume especially in summer. I am now waiting for a storage devise like powerwall by Tesla.

You have now lead me to a different ball park. I know nothing about variable frequency generators ( I think) and will have to do some research. To which dc output are you referring to, to connect the vfg?

Thanks once again

Don
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Re: Using the battery as an emergency supply

Sat Jun 10, 2017 9:06 am

SOC = State Of Charge. Aerowhatt's idea is very valid and should work for you. His suggesting of keeping the deep cycle battery between 30% and 80% SOC would work if you are using a lithium battery to power your inverter, but if you're using an ordinary lead acid battery (much cheaper) then 50% to 90% would be a better number. Lead acid batteries lose lots of life if discharged to 30% in deep cycle applications

Don
2012 iMiEV SE Premium, White
2012 iMiEV SE, White
2017 Chevy Volt Premier
2014 Ford Transit Connect XLT SWB wagon, 14,000 miles
1979 Honda CBX six into six

Aerowhatt
Gold Member
Posts: 411
Joined: Wed Jan 28, 2015 1:52 pm

Re: Using the battery as an emergency supply

Sat Jun 10, 2017 12:06 pm

9h1bw wrote:Aerowhatt,

Do you know what is the transfer rate of the iMiev dc to dc converter?
It is rated for an output of 80 amps and 14.4 volts . . . However as measured those are a bit off

BTW what does SOC stand for ?
As Don pointed out it refers to state of charge: 100% is full and 0% is empty

This solution is cheaper than using a dc to ac converter.
It is the cheapest easiest way to use the big traction battery for reasonably small back up loads. Whether you need to run AC or DC loads. It would probably help more to have a clearer picture of what your goals are for back up power


Aerowhatt
2014 cool silver ES, acquired new 4/2015
2014 Labrador Black Pearl ES, acquired new 3/2016

kiev
Posts: 662
Joined: Sun May 03, 2015 7:15 am
Location: The Heart o' Dixie
Contact: Website

Re: Using the battery as an emergency supply

Sat Jun 10, 2017 2:18 pm

The VFD approach would use the traction pack at 360VDC to connect directly to the internal dc buss of the VFD, bypassing the rectifier section used for ac input power. The VFD doesn't know or care where the dc buss voltage came from. Usually it it held up with large electrolytic caps also. Not for the faint of heart to stick hands inside an inverter.

i like the Aerowatt approach, easier and likely less cost.
kiev = kenny's innovative electric vehicle

9h1bw
Posts: 27
Joined: Sun Mar 19, 2017 2:35 am

Re: Using the battery as an emergency supply

Sun Jun 11, 2017 2:39 am

Thank you all for your input. I now have a lot of information to consider and experimention to carry out.

This is an excellent site to bounce off problems and ideas.

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