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Leaving chargers hooked up

Posted: Wed, 06 May 2015, 06:01
by jonescg
Hi All,

As many might know I have been heavily involved in the RAC Electric Highway, and we are in the process of finalising the power demands of specific sites. It seems some sites might have poor access to power, requiring upgrades to the local grid (transformers, DB boards, Domes etc).

Something we made clear from the very beginning was that a battery buffered system, ideally solar charged, would almost completely remove the need for a grid connection and in many cases, be cheaper. Now, councils considering such a system are going to put the design and installation out to tender, but how about a home-brew system?

So if you were to design a battery buffered, solar powered, heavy load supply, how would you do it and what could you do to make it 100% reliable?
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Most fast chargers take 3 phase + neutral, pass it through an isolating transformer, and then rectify this into DC. The DC then supplies the bus of the switched power supply. Since they have an upper voltage output of 500 V, an approximately 550 V bus is needed.

Could you not have a large battery of say, 50-60 kWh, and 550 V nominal voltage, across the DC output of the full wave rectifier? This battery is also constantly hooked up to a ~7 kW charger which maintains the nominal 3.3 V.

A few isolating contactors in the system wouldn't go astray, but it seems like it could work? The fast charger would still need some AC input to run the electronics, although this is no doubt a 12 V supply at some point.

Any thoughts?

Leaving chargers hooked up

Posted: Wed, 06 May 2015, 21:22
by Sutho
Hey Chris,

This is exactly what my DC Fast Charger for the ELMOFO Radical is.

It is a grid-independent 100kW DC Fast Charger with a 62kWh ELMOFO/Kokam High Power Lithium Pack.

It's fully adjustable....but we run at charge rates of up to 250A at 400V!

When we are at the track for a full day of racing, we generally plug into a 3-phase supply to trickle charge (8 to 24kW) the pack to ensure we are able to recharge the car up to 5 times in a day.

The work is all done. Image

Regards,
Brett

Leaving chargers hooked up

Posted: Thu, 07 May 2015, 03:09
by jonescg
I know it has been done, and there are companies who will do it (including ELMOFO), but I guess my question is - is it as simple as hooking up 600 V battery to the DC bus of the charger? Does the charger need any specific software changes to deal with the new power supply.

After all, battery chargers are really just switched power supplies with a variable voltage output.

Oh and does your ELMOFO charger support ChaDeMo and SAE Combo-1? If it does, you should put in a tender Image

Leaving chargers hooked up

Posted: Thu, 07 May 2015, 03:55
by reecho
I think a direct DC bus is possible on most if not all DCFC's. The operating firmware(s) would need to be modified to suit of course. Tritium says it's fairly easy on the Veefil. Cir control Trio's shouldn't be much different...

Image

At least initially capacity will be OK as the numbers of EV's aren't great. But there would be a tipping point down the track where the charging (recovery) time won't be able to keep up???


Leaving chargers hooked up

Posted: Thu, 07 May 2015, 05:27
by jonescg
Yes Circontrol told me it would be possible, but not as simple as it sounds. I assume it's because it needs to sense the supply voltages... but they seemed perplexed as to why you would do it. "Don't you have power in WA?" Image As it turns out, no, we don't have much of the stuff.

It's quite likely that battery buffered systems will be the way to go wherever a decent 3 phase connection is hard to find. And I reckon a 60 kWh pack would be fine for the most part. Two Leafs would drain it down to 20 kWh in an hour, but in that hour you'd put another 7-10 kWh back in. (A bit like "two standard drinks in the first hour, then one every hour" Image) No reason you can't add a second battery in parallel later on if you needed it.

Could you use a 24 kVA connection in conjunction with a 10 kW PV array to get 34 kW charging? I know that the EMC guys have set up solar water pumps with 400 V PV arrays directly feeding a VFD. Pump runs great 7 hours a day.

Leaving chargers hooked up

Posted: Thu, 07 May 2015, 17:40
by Sutho
jonescg wrote:Oh and does your ELMOFO charger support ChaDeMo and SAE Combo-1? If it does, you should put in a tender Image


It was designed to support CHAdeMO, but it has not yet been implemented.

Leaving chargers hooked up

Posted: Thu, 07 May 2015, 18:00
by reecho
Actually thinking about it......

The Mennekes fast AC wouldn't be able to function on pure DC battery backed.

But I guess you could use a combination of DC battery backed for DC feeds and grid connected AC for Mennekes??

So maybe 30KW 3 phase supply required for battery charging and Type 2 22Kw charging...

Leaving chargers hooked up

Posted: Thu, 07 May 2015, 18:39
by jonescg
Yeah, you would set the fast AC up to a 32 A three-phase grid connection for 22 kW charging and the Fast DC would run off the battery. The electronics still need a 230 V supply, so this could just come from the L+N supply.