how to disconnect battery

[Hedges]

My car starting battery is probably 30Ah, and 700 CCA. Two of them in parallel for a diesel pickup.
I had a 100Ah AGM bank for PV, now 400 Ah AGM.
There's a table down in this link:

Battery Internal Resistance & Short Circuit Current.

A study of battery internal resistance and short circuit current discussing how manufacturers calculate these values.

www.blueboxbatteries.co.uk

100 Ah AGM, 4100 amp short circuit current. So my 400 Ah might be 16000 amp short circuit.

The Square D QO has a DC interrupt rating good enough for the 100 Ah bank, but it isn't enough for the 400 Ah one.
10 to 30A breakers have 4000A interrupting, barely enough for the 100 Ah. 35 to 70A have 10000A interrupt rating.
These breakers would be OK for PV disconnect if Voc low enough.

Are QO load centers suitable for use on a 125V DC application? | Schneider Electric USA

https://download.schneider-electric.com/files?p_enDocType=Data+Bulletin&p_File_Name=0601DB0401.pdf&p_Doc_Ref=0601DB0401

Class T - yes, that is what I use. 20,000A interrupt rating.
I guess anything larger than 400 Ah or 500 Ah AGM would be too big.
Lithium possibly even smaller.

Class T Fuse - 350 Amp - Blue Sea Systems

Use with Class T Fuse Blocks for circuit protection of devices including inverters. high interrupt capacity for large battery banks including Lithium-ion and TPPL batteries.

www.bluesea.com

 

[salve]

With battery it is good practice to disconnect the negative first and connect the negative last.

back in the day, we were always told to put take negative off first, and put back on last when swapping out batteries in cars. I assume your inverter has no power switch?

Thanks very much you guys. You really helped me out.
I don't know why you asked but my inverter does have a power switch.

 

[Hedges]

Power switch is good to make sure no current flow while battery cable disconnected or connected.
Arcs can do nasty things to electronics (higher frequencies and voltage spikes)

The other thing is to not cause a short with the wrench! That's why negative first in a car - if the wrench hits (negative grounded) chassis, no harm done.

 

[curiouscarbon]

My favorite solution is to have a three position switch right at the battery positive. One position is off. One position is a small bulb or 4W resistor to prevent spark from inverter capacitor charging. Third position is on, straight connection.

Turn off sequence; rotate switch from on to off, disconnect cable.

Turn on sequence: switch off, attach cable. rotate switch from off to precharge/resistor for a minute. This charges inverter capacitor no spark. Then switch to on and begin operation.


Input: battery
Output 1: resistor/lamp to inverter
Output 2: high gauge wire to inverter

 

[Zil]

That is an interesting use of battery switches. I have a 2000W inverter and don't worry much about the SPST switch sparking. Blue Sea switches. I would worry more with cheaper switches.

 

[Hedges]

Guess we could just add a pushbutton to lightbulb in parallel with a single switch.

Caps may not like the surge current delivered by a battery, especially the higher current from lithium and with low battery cable resistance/inductance. I would assume, though, inverters are designed and tested for a typical battery input and got cycled a number of times.

Something else I would worry about is brown-out of power to some switchers inside an inverter. Those which wake up and run electronics while not producing AC would have a low power 48V (or whatever) input, 5V (or whatever) output. Some switcher modules have a minimum input spec and kill themselves below that. Quality inverters ought to have a power-good circuit as well. But charge through a resistor, and every time circuit starts drawing current the voltage could go low again (depending on resistance value.)

I was thinking about this for gently applying voltage to input of an inverter that had been out of use for years. Electrolytic caps sometimes need re-forming this way.