Load Shedding Contactor

[Salts]

I'm installing a couple of Sunny Island 6048 inverters and want to put in a Load Shedding Contactor to disconnect the house if battery voltage gets too low.

Is this just a normal contactor with properly rated contacts? I'm looking at some used 3 phase Allen Bradley contactors with 48v DC coils (my disconnect voltage is 41v). The contactor is rated at 125 Amps non-inductive (or) slightly inductive and 75 amps for inductive loads like motors.

I'm "assuming" this will be more than good enough for an inverter that only puts out 38 amps @240vac, but I wanted some input in case I'm failing to consider some aspect of this. While its a 3 phase contactor, I obviously plan to use only two of the contacts.

Nice thing about it is that it also has aux contacts so I can wire up an external indicator.. or just use the third pole for it.

[Mike90250]

I suppose those contactors would work on your 120VAC lines. Are you thinking of disabling only heavy loads, to conserve power to keep the critical loads (beer cooler) & sports channel going, without the inverter shutting off from low voltage ?

Also, a 48Vdc coil can see up to 60V when batteries are equalizing, and may not release till 30V. They are not calibrated to act as a voltage sensitive relay.

[Salts]

I suppose those contactors would work on your 120VAC lines. Are you thinking of disabling only heavy loads, to conserve power to keep the critical loads (beer cooler) & sports channel going, without the inverter shutting off from low voltage ?

Also, a 48Vdc coil can see up to 60V when batteries are equalizing, and may not release till 30V. They are not calibrated to act as a voltage sensitive relay.

I plan on shutting down all loads. If something is that critical, I'll run the generator. The Sunny Island has an option to activate a Load Shedding Relay all on its own. This preserves the power to the Sunny Island so that it can continue charging the batteries when a power source becomes available.

The battery is a lithium ion battery from a Chevy Volt. Its configured in a 12s 45ah format with 8 individual strings. Shut down will be set at 42 volts or 3.5 volts per cell. (no where near the bottom of the actual battery specs). At the top, 4.1 volts per cell, the pack is at 49.2 volts.

So as long as the contactor operates on command between 42 and 50 volts, I should be fine.

Just wanted to pick brains in case there is something I haven't thought of. Thank you for ringing in.

[Ampster]

I assume you are shutting down the 240/120 volt AC loads using the LVC disconnect signal from your inverter? Is that 60 volts? If I remember you also have a BMS. I am not sure I understand why you are using a 60 volt coil but with enough relays it doesn't matter if the triggering source is dry contact or 12 v or 60v. I assume you are using a contactor because you want it to be fail safe? What I mean is that if you lose the voltage holding the contactor closed it will open the contactor and drop the loads.

[Salts]

I assume you are shutting down the 240/120 volt AC loads using the LVC disconnect signal from your inverter? Is that 60 volts? If I remember you also have a BMS. I am not sure I understand why you are using a 60 volt coil but with enough relays it doesn't matter if the triggering source is dry contact or 12 v or 60v. I assume you are using a contactor because you want it to be fail safe? What I mean is that if you lose the voltage holding the contactor closed it will open the contactor and drop the loads.

The Sunny Island has a couple of multi-function relays inside that can be programmed to perform a variety of functions. One of these functions is called "Load Shedding". If the battery voltage sinks to low, it will open a contactor to break the power going to the distribution panel. The Sunny Island will not shut down itself until it reaches 41 volts. The Load Shedding contactor prevents the Sunny Island from reaching that point.

The idea is that if the Sunny Island shuts down, then there is no way to charge batteries in an AC coupled system. You'd have to hook a charger directly to the batteries and find a way to power it until the charger can bring the voltage back up where the Sunny Island would do a restart.

My system is 45 volts nominal. 12s Lithium cells from a Chevy Volt battery.

Hmm.. not sure if this is fail safe or not. The Sunny Island must hold an internal relay closed which sends battery juice to the 48vdc contactor coils. If the SI opens the small internal relay, the battery juice doesn't get to the load shed contactor and it then opens.

If the small internal relay in the SI malfunctions (contacts welded shut for some odd reason), then the SI will still shut down at 41 volts no matter what.. and if that somehow fails (a really bad day), then the BMS on the battery is the last line of defense. And its not some cheap china stuff, I'm using a Rec-BMS with a Kilovac contactor.

If everything fails, the battery is contained in a 3ft x 4ft Hoffman 14ga steel box. I'm considering installing a standard industrial fire sprinkler inside it. Won't stop the fire, but it will cool things down.

[kjtwist]

I've been trying to deal with this issue myself. I want to shut off my charge controller if the battery charge gets too high. I've tried different contactors with a voltage relay but the contactors will seize every time. The secret I'm told it to have a pre-charge contactor with a resistor to limit the in-rush current between the batteries and the inverter. I was given this diagram, which shows 2 contactors and a resistor but not being an electrical engineer I don't know exactly what this will look like in the real world. Here's what I've tried and the diagram shows what I'm told I need.

[Ampster]

A recharge resistor will reduce spark on contactors when closing (starting). I am not sure that will affect the contactor when disconnecting under load. I have used Kilovac brand of contactors which are designed to quench the spark. Perhaps getting a better contactor woul be more optimal than some pre charge resistor experiment.