Inverter/converter and battery DC connections

[fran&frank]

I'd appreciate input on my schematic for the DC connections on my planned Lithium battery and inverter/converter install. In another post I'll explain why I chose Lithionics batteries with their internal BMS, but for now just want to be sure I've got my wiring correct. A couple of questions: I know I need 4/0 cable or equivalent sized copper bar between the converter and the battery, but does the cable running to the chassis ground also have to be that heavy? Also I have disconnects so I can disconenct the inverter charger or disconnect the battery, would it also be a good idea to add one to the input from the solar charger? And thanks to everyone who has answered earler questions and gotten me this far! On the AC side I am putting in a split distribution panel to accomodate the inverter and non-inverter powered ciruits--Frank

[Snowy]

Hi Frank

Looks good, puts my schematics to shame nice and graphical.

You should fuse connections to the positive bus bar be it a source or sink. aka, feed or drain. The connection to the solar charger should have a fuse inline whos size will be dependent on the chargers max output (or max wire size capacity).

The connection does not have to be the same as the main cables unless you plan to use the chassis as a return path someplace else with high current.

[fran&frank]

Thanks for the input Snowy. I am planning on putting a 60 A circuit breaker on the line from the solar charger, the other two circuits are existing circuits but I will confirm they are fused.--Frank

[mythbuster88]

Frank and Fran,

You asked about switches and I think Snowy is using circuit breakers to be both fuses and switches.

Also Snowy uses a shunt to get an accurate measure of current. A great idea to know what is really going on with your batteries.

http://www.airforums.com/forums/f449...ud-163074.html

I can't comment on your drawing as I'm still on training wheels here and just learned that DC to AC is an inversion and AC to DC is conversion.

RC

[mythbuster88]

Frank & Fran,

Oops you have as shunt!
Forget that last post!


RC

[Scorge-ION]

First, I’ll praise you for drawing a schematic.
Second, I hope you have the appropriate safety gear: gloves, hearing protection, face shield, etc., for defending against arc flash. Don’t ask me how I know. If it’s enough current to require 4/0, an electrical short will cause an arc flash like you wouldn’t believe, even with low voltage DC. BTW, arc welders use low voltage and huge currents.
Third, you don’t need a switch in the return line, only in the hot line. The fewer devices and connections and splices, the more reliable the installation will be.
Fourth, yes, always use a ground wire of the same size – OR LARGER – for safety. You wouldn’t want a ground fault to set your ground wire on fire!
Fifth, tap the distribution from between the cutoff switch and the main fuse, not between the switch and the battery. This will be so the loads don’t drain the battery while the inverter-rectifier is unplugged from shore power and the battery is shut off. The basic reason for the shutoff switch is to prevent battery discharge.
Sixth, check with the manufacturer about switching out the battery while the rectifier is operating. This may be inadvisable; I don’t think so but I don’t know. You don’t get old by being stupid.
Seventh, be cautious about charging the house battery from the tow vehicle and vice verse. The currents can easily exceed the wire’s ampacity. The kit I installed in my old pickup had a dainty 12-AWG wire for the trailer charging circuit. Unacceptable!
Eighth, yes you will probably want a connector to disconnect the photovoltaics.


Best regards, Dave the Scourge of the ION

[Snowy]

Originally Posted by Scorge-ION

Third, you don’t need a switch in the return line, only in the hot line. The fewer devices and connections and splices, the more reliable the installation will be.


Fifth, tap the distribution from between the cutoff switch and the main fuse, not between the switch and the battery. This will be so the loads don’t drain the battery while the inverter-rectifier is unplugged from shore power and the battery is shut off. The basic reason for the shutoff switch is to prevent battery discharge.

Best regards, Dave the Scourge of the ION

Keeping the switch in the return line alleviates issues with the setup as proposed.

The reason for the loads before the positive switch is that I assume they want them connected most of the time and only disconnect downstream things. Solar connected direct, trailer DC for converter charging via the AS disconnect direct. Etc etc etc.

If a total disconnect is wanted, flip the negative switch.

Good flexibility with the setup as proposed if you ask me.

[Troutboy]

Fran&frank, do you have pricing on that big battery yet?

[fran&frank]

Scorge-ION my thinking was that the disconnect on the negative side would completely disconnect the battery and prevent any discharge. The disconnect on the positive side was to disconnect the inverter/charger from the battery if there was ever a need and the taps for other DC circuits were between it and the battery so they could still be used even if the inverter was disconnected. Thanks for the comments--Frank

[Scorge-ION]

Frank & Fran,
My bad. I didn’t know your concept of operation. I assumed (!) you would want the inverter available to run off the battery any time you are using the other DC loads.
Remember that each switch or other connection you add will introduce resistance and even tiny resistances will be problematic at the high currents you can expect. The current sensor, I assume (again!) is a standard .01 ohm resistor. Your inverter is rated to deliver 6 kWpeak and, assuming near perfect power conversion, would require 500 A from your battery. 500 A x .01 ohm = 5 V drop. When you only have 13.2 volts to begin with, that could be a deal-breaker!
More realistically, you should derate the inverter to about 2 kWcontinuous, at which point the resistor will be dropping only 5/3 of a volt.
Now, I ordinarily have to take serious actions to get my electrical connections below about .1 ohm. Consider silver plating your 3/16”x1” copper bar. The silver will also help keep copper corrosion down. The heat and humidity of Mississippi makes stuff corrode quickly. I also recommend Cool-Amp silver plating and Conducto-Lube silver lubricant/grease. Also consider replacing the steel screws and bolts with bronze for the higher conductivity. And seal off your connections with Sanchem A-Special to keep them from corroding.
Alternatively, you could use higher battery voltage to operate the inverter. Your inverter can use either 12 or 24 volt batteries. Cutting the current requirements in half by doubling the voltage would solve many problems.
48 Vdc would be optimal if you can find an inverter-rectifier unit you like. 50 volts is the internationally recognized boundary between low- and high-voltage. (Everyone lets it skate through even though it exceeds the 50-volt limit while charging.) Low-voltage means it’s not life-threatening although the back of my right hand always hurts when I remember the times I put it across the 48-volt terminals.
Keep in touch and let us know how it turns out.
Dave, the Scourge of the ION