# Charging electric car batteries with ?portable? battery packs



## dobrobegood (Nov 12, 2013)

*Charging electric car batteries with “portable” battery packs*

Hello everybody,
I would like to ask you an opinion about this idea I am working on in the last period, most of all I am not completely sure about the technical feasibility of it, so any information from you is precious for me!!
The idea is very simple: in case an electric car runs out of battery in a place in which there is no charging station, I would like to have some kind of portable battery pack which I can plug into the electric car for some hours, so that it can charge it again and make it move. In order to do it I would need:

A battery pack with a standard plug so that it can be capable of recharging the highest number of electric cars
A VAN or a pick-up in which I can load and unload the portable battery pack, so that I can leave the battery pack in charge until it comes the moment in which I need it

I sounds to me like something possible, like when a laptop PC recharge a smartphone through USB cable: it is a battery (the laptop one) recharging another one (the smartphone one). I know that electric car batteries have pretty big size and weight, so I would like to understand better how can it work and in case how many portable battery packs I can load/unload on a single VAN.
*If we take as example the lithium-ion battery of the Smart Electric Drive (16,7 kWh capacity) how much would weight a portable battery pack capable of recharging it? Which size could it have? How many time should it be connected to completely charge the Smart Electric Drive battery*?

Please feel free to write any observation, doubt or proposal,
And most of all… thank you in advance for any help! 
Paolo


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## Frank (Dec 6, 2008)

This is called "dump charging" and it's not a new idea. Lots of racers do it. You still need a charger that can accept DC input (sometimes with internal mods) and that's what controls the charge rate. Your recharge pack would have to be sized accordingly. You would have to know max allowable charge rate for the subject vehicle too. It could be an interesting service to offer though. I believe this is the basis for Tesla's "supercharger" stations that are popping up.


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## dobrobegood (Nov 12, 2013)

*Re: Charging electric car batteries with “portable” battery packs*



Frank said:


> This is called "dump charging" and it's not a new idea. Lots of racers do it. You still need a charger that can accept DC input (sometimes with internal mods) and that's what controls the charge rate. Your recharge pack would have to be sized accordingly. You would have to know max allowable charge rate for the subject vehicle too. It could be an interesting service to offer though. I believe this is the basis for Tesla's "supercharger" stations that are popping up.


Hello Frank,
thanks for your answer I didn’t ever searched for “dump charging” and thanks to you I am finding a lot of additional very useful information.
My idea is different from a battery-swap service or any other recharge way mostly because I would like to LEAVE the battery pack plugged into people cars for hours and then come back and retrieve it. This let me serve a lot of (potential) customers contemporarily but it strongly depends on the size & weight of the portable battery pack that I would load on the VAN/pick-up.

I believe that as Tesla is making everything in house, their “smart grids” and “superchargers” are fully made for a Tesla car architecture. On the other hand I think this could be a useful service for any other electric car owner and so I am investigating the technical feasibility of it, especially in terms of size & weight.

Where do you think I can get the max allowable charge rate for electric cars which are currently commercially available? I was trying to get it on the Smart Electric Drive page but I just found the battery capacity (16,7 kWh). 

Thanks,
Paolo


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## Frank (Dec 6, 2008)

*Re: Charging electric car batteries with “portable” battery packs*

One way to get that information is to take their "time to recharge" information and back-calculate. For example, if they say you can recharge in 8 hours, assume it's pretty much from "empty" (let's say 16 kwh in this case) so that's 2kwh/h. You can calculate from there the current depending on supply voltage and assuming some inefficiency.

If you're thinking of a recharge service (ex. when people are at work) you would have to have a lot of capital investment. You might be better off offering a quick-charge service. Great to see you thinking out-of-the-box though!


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## ga2500ev (Apr 20, 2008)

*Re: Charging electric car batteries with “portable” battery packs*



dobrobegood said:


> Hello Frank,
> thanks for your answer I didn’t ever searched for “dump charging” and thanks to you I am finding a lot of additional very useful information.
> My idea is different from a battery-swap service or any other recharge way mostly because I would like to LEAVE the battery pack plugged into people cars for hours and then come back and retrieve it. This let me serve a lot of (potential) customers contemporarily but it strongly depends on the size & weight of the portable battery pack that I would load on the VAN/pick-up.


I think you are going to have a consumer challenge with this model because your customers are not going to want to have to wait for a recharge. This is the reason that battery swaps are usually considered in this arena.

The next biggest problem is that the recharge rate depends on the internal charger of the vehicle, not the capacity of the charging source. You can hook up a 100 kWh pack to a Nissan leaf, but it will not charge any faster than the 3.3 kWh rate of its internal charger.

ga2500ev


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## DavidDymaxion (Dec 1, 2008)

*Re: Charging electric car batteries with “portable” battery packs*

If the electric car has regen, you can do "tow regen." You tow the car to charge it. I did it on my car before, and charging was far faster than anything you'd plug in to charge.

Another idea for you, it might work well to have an electric car with a huge capacity pack to quick charge another electric car.


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## peterguy (Jun 18, 2012)

*Re: Charging electric car batteries with “portable” battery packs*

You're thinking about something like this?
http://www.toyota-motorsport.com/en...le-technology-en/off-grid-dc-quick-charger-en

For such a system you "just" need:
1) a big battery pack, preferable with a voltage higher than the one of your EV's battery .
2) A DC/DC or DC/AC converter that is compatible with the Charger interface of your EV
3) An AC/DC Converter to recharge the backup batteries.
4) Some relays, control logic and so on to put the system alive.


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## PStechPaul (May 1, 2012)

*Re: Charging electric car batteries with “portable” battery packs*

Such a van could contain two battery packs (or one very large one) as well as a motor-generator set so that it could self-recharge in remote areas without grid access. Thus it could be an EV which can use quick charge stations or grid electricity, and it should be able to recharge quickly or charge the stranded vehicle quickly. Having a service like this available would help ease range anxiety, and might be a lucrative business.


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## moneyfink (Oct 23, 2016)

*Re: Charging electric car batteries with “portable” battery packs*

Sorry to reply to such an old thread. I work in electronics recycling and have access to 5,000 lbs of laptop batteries per month. I was looking to dismantle batteries and test the cells. With the best cells, I want to build a 5-10 kWh battery pack to use as a range extender for a 2013 Nissan LEAF or Mitsubishi I-MiEV. I've been in the planning phase for a few weeks now. I feel confident that I can build the pack. I am not as confident in my ability to interface the two batteries in the way I want to. If anybody can help or point me to resources, it would be greatly appreciated.


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## Northbynortheast (Nov 29, 2018)

Did you get anywhere with this idea money fink? I was thinking of the same thing for my 2014 Leaf: electric jerry cans to give me a few more miles.


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