Using the battery as an emergency supply

[9h1bw]

Since my last post I carried out a test to see how efficient it is to use the auxiliary battery to generate a supply in the field. In my case as a supply for my ham radio activity.

I attached a car head lamp to the auxiliary battery and measured the voltage, current, and power in watts. I turned on the ignition to Ready and took measurements every 15min until the fuel gauge notch when down by one. I previously charged the battery to full to start from a maximum supply.

The voltage during the period was 13.96 volts. Thus the dc to dc converter was operational. The current marked 4.3 amps. Thus the bulb consumed 60.73 watts. I took 4.25 hours to consume one notch. Hence the load consumed 258 w/hrs.

To control the power consumption figure I recharged the battery to full and measured the kw/hr to obtain full charge. This marked 1.49kw/hr.

My question is if I used 258w/hr to light the bulb why it took 1.49kw/hr to replenish the Battery? I would assume that the two figures to be close. What is consuming power to make up the difference?

 

[phb10186]

All the auxiliary electrical hardware associated with running all the HVAC systems, as well as the 12V DC side of things. You are in effect doing something like running your whole desktop PC to power a USB light.

I wonder how sensible it is to keep the car in ready mode for an extended period of time?

 

[Don]

Topping off and balancing the traction battery takes more power than you actually used and fully recharging it when you've only used ~5% of it's capacity is going to give you a horrible ratio - Mitsu advises not to plug it in when the traction battery is nearly full. The 12 volt power you used was generated by the DC to DC converter which is probably only 80% efficient. Keeping the car in the 'Ready' mode the entire time has many other things running which are using power

I think if you did full capacity test, i.e. running long enough to take the traction battery down to a low level and then recharged it fully, you could get a ratio closer to 2:1 instead of the 6:1 you got with your short test . . . . but that's just a guess

Don

 

[9h1bw]

Thank you both for your replies. Which mirror each other.

It all started out from the fact that Mitshubishi has produced for the Japanese market after the zunami to give distributed power during the emergency. However they never produced it for other markets.

Thus my idea is a non starter.

Thank you for your help.

 

[kiev]

That was interesting experiment, thanks for sharing.

If you had an inverter then you could generate 120vac to run appliances in your home or ham radio event.

With a high voltage inverter this could be powered from the main pack (360VDC) thru the Chademo port--i would guess that was the tsunami concept.

 

[9h1bw]

Kiev,

Thank you for your suggestion. I would need to find an inverter which has 340v dc input to 230v ac output. I have never seen one on ebay. Any suggestions?

 

[Don]

I suspect you would have to build your own inverter . . . . and then you may find you would need some circuitry to enable the high voltage at the DCQC connector - I doubt it's present until a relay is closed

A lot of time, trouble and money for an emergency supply which I trust would not be used very often. The traction battery only has just so many charge/discharge cycles in it before it's depleted. Using those up for something other than driving the car might leave you with a pretty nice car with few miles on it and an unusable battery. The price of a new battery would likely 'total' the car and it would be junk :shock:

4 golf cart batteries in series parallel to run a 12 volt to 120 VAC inverter (or in series with a 24 volt inverter) would probably run your Ham rig all day and at a much lower price . . . . or maybe a little 1 Kw inverter/generator with a 100 foot extension cord. That's the set-up I often see at Hamfests

Don

 

[kiev]

How much power do you need for your application? There are different sizes and suppliers...

http://www.electriccarpartscompany.com/2.8kW-GW-Inverter

 

[Don]

Amazing find! - That would sure do the job and for a small fraction of the price of the OEM Mitsu unit . . . . which isn't even available here

Wonder hoe much a DCQC plug to go with it would cost?

Don

 

[9h1bw]

Kiev,

That is a very interesting option. I would say it should suffice for power as it would consume two notches on the fuel meter and give me 24 hour of autonomy. I need around 120w/hr. I would need to find a 230 v ac at 50 hz one so as not to burn out my equipment. Most of it is rated at 220 volts . It is only in receipt years that the eu standardised to 230 volts.

The price is a problem since it is not sure that the improved power transfer would work and $700 + plus shipping and tax would break the bank for just an experiment at this point in time. It would be cheaper to buy lithium batteries and a solar panel.

Still thank you for your efforts. If any of you comes up with a cheaper option please inform me.
BTW I charge my iMiev with solar power.

Thank you all for your input.

 

[Aerowhatt]

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

 

[kiev]

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.

 

[9h1bw]

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]

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]

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

 

[Aerowhatt]

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

 

[kiev]

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.

 

[9h1bw]

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.