Opinion on stacking lug terminals on inverter post?

[DurkaDurka]

I have a Victron 100/50 MPPT and Giandel 2200 watt inverter that need to be attached to a 12 V battery. Opinions on stacking 1/0 and 8 gauge tinned copper lug terminals on the inverter 12V terminals? I can easily offset them 30-45 degrees to keep the terminals flat. The 1/0 is battery side, the 8 is MPPT side. Cables are under 2 - 5 ft (round trip). Current on inverter side will not exceed 125A (intended draw is well under 1500 watts).

I'm hoping to avoid a bus bar as I don't intend to wire any other high current devices on the 12 V side.

 

[sunshine_eggo]

I would use ring terminals with smaller holes. Those are way too big for that terminal.

Aside from that, go for it. You will need a fuse or breaker on each (+) wire.

 

[DurkaDurka]

I would use ring terminals with smaller holes. Those are way too big for that terminal.

Aside from that, go for it. You will need a fuse or breaker on each (+) wire.

These are 3/8" holes in the terminals...what size you recommend? Fuses are in place before this on both sides.

 

[sunshine_eggo]

These are 3/8" holes in the terminals...what size you recommend? Fuses are in place before this on both sides.

What size is the stud?

 

[Ampster]

The point is you are losing valuable contact surface area by using oversize lugs. They should be the same size as the studs.

 

[DurkaDurka]

What size is the stud?

The inverter came with two cables. Each cable is 2 "bonded" 16mm (~ 6 AWG) cables connected to a 1/4" terminal (inverter side) and 3/8" terminal (battery side). I'm not sure I trust the cable, plus they are too long.

If I were to get 1/4" 1/0 and 8 AWG terminal lugs, is this configuration safe/efficient?

 

[sunshine_eggo]

The inverter came with two cables. Each cable is 2 "bonded" 16mm (~ 6 AWG) cables connected to a 1/4" terminal (inverter side) and 3/8" terminal (battery side). I'm not sure I trust the cable, plus they are too long.

If I were to get 1/4" 1/0 and 8 AWG terminal lugs, is this configuration safe/efficient?

Yep.

 

[John Frum]

2200 ac watts / .85 inverter efficiency / 10 volts low cutoff = 258.823529412 service amps
258.823529412 service amps / .8 fuse headroom = 323.529411765 fault amps

That means pure copper 3/0 awg cable with 105C insulation and a 350 amp fuse minimum for the battery to inverter circuit.
Preferably fused as close to the battery positive terminal as possible.

You are also going to need a serious battery to satisfy that inverter.

 

[Warpspeed]

The bolt is only there to keep the lugs pressed tightly to the underlying terminal and any other lugs.
That still works with a larger hole, provided there is a sufficiently large and thick steel washer under the nut to cover the lug.

Naturally good workmanship really demands the correct lugs to suit both cable and bolt sizes, but as long as the lug is pressed tightly down over its entire flat surface, a smaller bolt and larger hole can still work.

 

[DurkaDurka]

The bolt is only there to keep the lugs pressed tightly to the underlying terminal and any other lugs.
That still works with a larger hole, provided there is a sufficiently large and thick steel washer under the nut to cover the lug.

Naturally good workmanship really demands the correct lugs to suit both cable and bolt sizes, but as long as the lug is pressed tightly down over its entire flat surface, a smaller bolt and larger hole can still work.

The 12V terminal plate is quite large, so the entire 3/8" 1/0 lug lays against metal. The washer, I was going to address for sure.

 

[sunshine_eggo]

The 12V terminal plate is quite large, so the entire 3/8" 1/0 lug lays against metal. The washer, I was going to address for sure.

Please confirm that you can see how you have more contact area with a 1/4" lug vs. a 3/8" lug.

Contact surface area and clamping pressure are key to making a good connection.

When you can see gaps between the washer OD and the terminal ID, you know you have the wrong ring terminal.

 

[DurkaDurka]

2200 ac watts / .85 inverter efficiency / 10 volts low cutoff = 258.823529412 service amps
258.823529412 service amps / .8 fuse headroom = 323.529411765 fault amps

That means pure copper 3/0 awg cable with 105C insulation and a 350 amp fuse minimum for the battery to inverter circuit.
Preferably fused as close to the battery positive terminal as possible.

You are also going to need a serious battery to satisfy that inverter.

Thanks for this. The converter shows 90% efficiency and I will be putting a GFCI that will not allow more than 120VAC / 15A draw. The intention right now is to draw no more than 500 watts (no load surge) - I went with a larger inverter to have plenty of headroom. That's about 35A @ 12V /w 90% efficiency...should hold for a good 2-3 hours on a 100Ah LiFePO4 battery. I intend to get another one once I settle things for a total of 200Ah. That should be at 4-6 hours sans solar input.

It may be a bit of a waste that I got a 12V inverter as I'd rather do 2 x 12V in series to cut amperage in half. For now, I have a 150A ANL fuse for the main battery. Thoughts? Maybe I should order a 250A. As for the wire, if a 1/0 doesn't work, can I double up the wires for more ampacity?

I also got an AiLi shunt monitor, so I intend to only use maybe 80% of the battery capacity before switching the load back to house AC.

 

[DurkaDurka]

Please confirm that you can see how you have more contact area with a 1/4" lug vs. a 3/8" lug.

Contact surface area and clamping pressure are key to making a good connection.

When you can see gaps between the washer OD and the terminal ID, you know you have the wrong ring terminal.

Yes, I understand a 1/4" lug will have more contact area. I'll try to source 1/4" 1/0 and 8 AWG terminals.

 

[sunshine_eggo]

Thanks for this. The converter shows 90% efficiency

90% is a maximum. It's typically at about 30% of rated continuous power. Below that, it can be very inefficient. At max output, it's going to be in the 80-85% range.

and I will be putting a GFCI that will not allow more than 120VAC / 15A draw.

That's still 120*15 / 12 / .85 = 176A

The intention right now is to draw no more than 500 watts (no load surge) - I went with a larger inverter to have plenty of headroom.

This can get you because larger inverters consume more idle power, i.e., they gobble power even if no loads are attached.

That's about 35A @ 12V /w 90% efficiency...should hold for a good 2-3 hours on a 100Ah LiFePO4 battery. I intend to get another one once I settle things for a total of 200Ah. That should be at 4-6 hours sans solar input.

It may be a bit of a waste that I got a 12V inverter as I'd rather do 2 x 12V in series to cut amperage in half. For now, I have a 150A ANL fuse for the main battery. Thoughts? Maybe I should order a 250A. As for the wire, if a 1/0 doesn't work, can I double up the wires for more ampacity?

If LFP battery, Class T are recommended as LFP batteries can deliver massive current in the event that their BMS fails.

I also got an AiLi shunt monitor, so I intend to only use maybe 80% of the battery capacity before switching the load back to house AC.

Good. Too many folks overlook the value of a decent battery monitor.

Yes, I understand a 1/4" lug will have more contact area. I'll try to source 1/4" 1/0 and 8 AWG terminals.

Coolio. If you ever plan to use more power than stated, it might be worth going to heavier wire per Smoov's suggestion.

 

[DurkaDurka]

Appreciate the comments. I am ordering the 1/4" copper lugs and a 250 ANL fuse. I understand class T fuse is better, is there one on Amazon you can recommend (I'll need the fuse block as well)?

BTW, 10' of red/black 4/0 copper wire on Amazon is $161!

 

[John Frum]

Thanks for this. The converter shows 90% efficiency and I will be putting a GFCI that will not allow more than 120VAC / 15A draw. The intention right now is to draw no more than 500 watts (no load surge) - I went with a larger inverter to have plenty of headroom. That's about 35A @ 12V /w 90% efficiency...should hold for a good 2-3 hours on a 100Ah LiFePO4 battery. I intend to get another one once I settle things for a total of 200Ah. That should be at 4-6 hours sans solar input.

It may be a bit of a waste that I got a 12V inverter as I'd rather do 2 x 12V in series to cut amperage in half. For now, I have a 150A ANL fuse for the main battery. Thoughts? Maybe I should order a 250A. As for the wire, if a 1/0 doesn't work, can I double up the wires for more ampacity?

Pure copper 1/0 awg wire with 105C insulation aka "the good stuff" can be fused up to 250amps.
That means 250 fault amps.
250 fault amps * .8 = 200 service amps.

That is a good size for the 2x 100ah batteries in parallel for which you plan.

 

[WYtreasure]

Appreciate the comments. I am ordering the 1/4" copper lugs and a 250 ANL fuse. I understand class T fuse is better, is there one on Amazon you can recommend (I'll need the fuse block as well)?

There's a link in my signature "battery melt down". It should offer some more info regarding the terminal connection question.

 

[DurkaDurka]

Pure copper 1/0 awg wire with 105C insulation aka "the good stuff" can be fused up to 250amps.
That means 250 fault amps.
250 fault amps * .8 = 200 service amps.

That is a good size for the 2x 100ah batteries in parallel for which you plan.

200 service amps by 12 V (really 12.8 V, no?) = 2,400. I'm quite happy with that since I'd never run the inverter more than about 80% capacity.

Edit - I already received 1/0 wire from windy nation on Amazon. The temp spec is indeed 105C and I intend to keep these runs short - hopefully under 2-3 ft round trip.

 

[DurkaDurka]

There's a link in my signature "battery melt down". It should offer some more info regarding the terminal connection question.

Thank you, this was a useful read. I certainly had no intention of putting the washer on the terminal side. DOH! With the new incoming 1/4" lugs, the service surface area laying on the terminal will increase and the washer that came with the inverter should put plenty of pressure on the lugs against the terminal. The manual did not provide a torque spec, so I guess I'll go "pretty darn tight".

 

[John Frum]

200 service amps by 12 V (really 12.8 V, no?) = 2,400. I'm quite happy with that since I'd never run the inverter more than about 80% capacity.

10 volts actually.
10 volts is the low voltage disconnect for your inverter and BMS.
BTW your BMS will very likely disconnect on cell under voltage before the inverter disconnects.
Doing that at significant current is absolutely brutal on the FET based BMSs in your batteries.
Typical scenario is one BMS disconnects on cell under voltage and the second BMS disconnects nearly immediately on over current.
Not a good day for either one.
FETs have a habit of failing closed which means your BMS may fail to protect your batteries and you won't know until the damage is done.