[RE-wrenches] Discharging a high voltage battery

Thu Feb 23 17:04:58 PST 2017

The idea is to use an inverter manually as a current dump to the grid from the EV battery as opposed to just driving around to discharge the battery. No automation or communication required. This is not for a permanent connection. So they will connect, discharge, then disconnect when done.

If the inverter regulates output based on its power capability, e.g. a 5kW inverter limits power to 5kW (as I’ve been told in on off-list response), then it really should not matter what the MPP circuits are doing. 

Mac Lewis,
Very nice offer. I’ll let them know.

Thanks everyone.

Larry

On Feb 23, 2017, at 4:37 PM, August Goers <august at luminalt.com> wrote:

Hi Larry,

I have no idea what would happen if you connected a DC high voltage (340 v) battery source to a PV inverter. I guess my point is that it isn’t designed for it and likely wouldn’t work. Maybe it would? I have to think that both the inverter and the EV would have some sort of logic or circuitry to prevent the inverter from just pulling juice from the battery. Regardless, the inverter wouldn’t have the controls setup to decide when to start inverting and when to stop. 

Technically, you might be right though – the MPPT circuit on the inverter might just sweep and invert. 

August

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org <mailto:re-wrenches-bounces at lists.re-wrenches.org>] On Behalf Of Starlight Solar Power Systems
Sent: Thursday, February 23, 2017 3:14 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Discharging a high voltage battery

Hello August,

Help me understand your point. If the MPPT circuit is sweeping, it will see the same voltage everywhere. Would it not just continue sweeping because it can’t lock on? Or perhaps it times out? As long as it is producing power during that process, won’t it be fine? 

Thanks to all for the responses. 

Larry

On Feb 22, 2017, at 1:04 PM, August Goers <august at luminalt.com <mailto:august at luminalt.com>> wrote:

Larry –

My immediate thought is that you would need a listed grid tied inverter designed for the purpose of connecting to this type of battery and inverting to the grid. A regular PV inverter won’t cut it since it is designed to MPT PV modules. 

The SolarEdge StorEdge product sounds like the closest thing on the market that might be close to working. But, once again, it needs to be setup to work with your particular battery. I think StorEdge is planning on working with Tesla and LG Chem RESU batteries in the 350 to 400 v range. 

August

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org <mailto:re-wrenches-bounces at lists.re-wrenches.org>] On Behalf Of Starlight Solar Power Systems
Sent: Wednesday, February 22, 2017 11:17 AM
To: RE-wrenches
Subject: [RE-wrenches] Discharging a high voltage battery

Hello Wrenches,

Someone has asked me about discharging their EV battery into the grid. They have an existing grit tie system. What they want to do is connect a 5kW grid tie inverter to their 340 volt, 32kWh EV battery bank and feed the grid to discharge the battery. Why was not discussed but sure bugs me. 

My uneducated guess is the inverter will be immediately damaged. My thought is how would it limit the input current? Or, is there such an inverter available that can do the job?

Any input is appreciated. 

Larry Crutcher
Starlight Solar Power Systems

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