inverter and battery ah requirements

jvincenzo · 03-13-2022, 07:41 PM

trying to upgrade my sg278 to do a little boondocking and i seem to have hit a snag…i purchased a 100ah lithium battery and will upgrade my converter/charger to a lithium model soon. in an effort to be able to “grow into” a more robust AC system, i went ahead and got a 3000w inverter from renogy.
we planned on buying more batteries over time as money permits.

i’ve got the battery hooked up with 1/0 cable, 4 feet long, on my bench.

What i’m seeing is that the inverter trips whenever i try to run anything larger then about 750w AC.

Seems like i should be able to use a 900w coffee maker for at least a few minutes!

i’m really new to this and would appreciate any thoughts or guidance!
thanks, jv

**JRTJH** · 03-13-2022, 08:02 PM

There are LED's on the faceplate of the inverter. You should have a green power on LED and the yellow and red LED's should be off. If the yellow LED is lit, it means you have a GFCI condition and the inverter is detecting a problem with the ground. If you wired it yourself, you may have a "crossed neutral/hot lead at one of the connections or at one of the plugs.

Have you tried to operate something simple like a 120 volt lamp ? Plug one into the outlet and see if you get the same condition. If so, it's likely a GFCI issue.

GHen · 03-13-2022, 09:35 PM

I am just getting ready to install my system, 420 AH lead acid, 3000 watt renogy inverter. I’ve been testing it on the bench for the last week with just a 75ah battery and experiencing similar results. I have a shunt installed and can see the voltage drop to below inverter minimums when I get to 1200 watts, I’m fine at 850.

First, should have bought the 2000 inverter, but on cyber Monday the 2000 was on back order so the DW bought the 3000w…. Should have returned it but the price was too good.

A 3000w inverter requires 4/0 lines (or double 2/0) with minimum 490 amp fuse, 4/0 can handle 500 amp if I remember correctly) from the battery due to peak draw. I don’t ever see pulling that much, but I’m wiring it per the required specifications. You could be having worse results that I am based on the small wire you have installed on your bench.

I’m expecting that once I’m hooked up to my 420 ah batteries I should be able to draw 1500amps without the inverter shutting down on “low voltage”, which is what I’m expecting is happening to you.

jvincenzo · 03-14-2022, 04:56 AM

i’m surprised that i’d need 4/0 on a run that short. the voltage drop on that length of cable shouldn’t put me outside of spec..and certainly not below the low voltage cutoff of the inverter…UNLESS i’m missing a a critical piece in my math, which is entirely possible. assuming that i follow the simple math(no account for efficiently of inverter)…A 1500w/120v ac load is about 12.5 amps on that side of the inverter . on the DC side, that should be around 125 amps being drawn. that’s within the spac of my battery. weize says the can draw 150amps before the bms cuts out.
it seems that this is far more complicated than it appears to be!
i’m stumped.

**flybouy** · 03-14-2022, 06:40 AM

Often appliances can have a high current inrush when first energized. This is a very common issue with microwave ovens. What's the SOC (state of charge) of the battery?

GHen · 03-14-2022, 07:28 AM

It took me a long time to confirm why most installs show using the 4/0 wires. And to make it more complicated some other manufacturers don’t recommend 4/0 until using inverters at 3500 watts. Since I know that I won’t be using the A/C and the microwave at the same time, I’m not concerned, BUT a 3000watt inverter has the capability. I should have just got a 2000w, especially with a lower parasitic draw when not in use.

First, I know there are a lot of opinions as to what you can get away with, I’m just using the facts of the specifications that you can look up on your own. The peak performance is also over a very short period of time and seems like melting wire or insulation may take more time.

The math is this, according to my inverter manufacturer, Renogy.

My 3000 watt inverter has a peak of 6000watts and it’s 95% efficient, so it needs 6300 watts peak going from the batteries to the inverter to make the 6000 watts.

If your solar charger is sending maximum voltage to the batteries, that’s up to 14.4 volts, so let’s just say it’s average is 13.6.

6300 watts divided by 13.6 is 463.2 Amps through the wires.
Even 3150 (nonPeak) watts divided by 13.6 is 231 amps.

According to the National electrical code
1/0 copper can handle 125 amps
4/0 copper can handle 195 amps

As you can see it’s complicated and confusing, so I just went with the recommended installation instructions for my inverter.

Maybe an electrician here can help explain it better.

With all that said, I’m just using 1/0 on parts of my bench testing. When testing at 1200 watts the wires get very warm and the inverter shuts downs due to low voltage in about 30 seconds.
Could have something to do with the Peukerts law, where your batteries will provide up to 25% less amps when the draw is high. I don’t know, I’m not an trained electrician.

snoobler · 03-14-2022, 09:17 AM

Quote:

Originally Posted by jvincenzo

trying to upgrade my sg278 to do a little boondocking and i seem to have hit a snag…i purchased a 100ah lithium battery and will upgrade my converter/charger to a lithium model soon. in an effort to be able to “grow into” a more robust AC system, i went ahead and got a 3000w inverter from renogy.
we planned on buying more batteries over time as money permits.

i’ve got the battery hooked up with 1/0 cable, 4 feet long, on my bench.

What i’m seeing is that the inverter trips whenever i try to run anything larger then about 750w AC.

Seems like i should be able to use a 900w coffee maker for at least a few minutes!

i’m really new to this and would appreciate any thoughts or guidance!
thanks, jv

Did you purchase a high quality LFP battery? Note that most 100ah batteries have a hard 100A output limit with very little tolerance for surge unless it's very short duration.

Have you properly torqued all connections? Insufficient clamping pressure at the connections can have massive resistance producing significant voltage drop.

Try this:

Get a voltmeter.

Under a 750W load, measure voltage AT the battery terminals and AT the inverter terminals.

https://www.calculator.net/voltage-d...=11&ctype=size

750W should pull about 69A @ 12.8V (LFP nominal). Your 1/0 wire should only show a 0.05V drop between the battery and inverter.

If you measure more than 0.05V difference, something is wrong.

snoobler · 03-14-2022, 09:18 AM

Quote:

Originally Posted by GHen

Could have something to do with the Peukerts law, where your batteries will provide up to 25% less amps when the draw is high. I don’t know, I’m not an trained electrician.

Peukert has negligible influence on LFP. The 100Ah rating is typically for a 100A (1C) discharge.

jvincenzo · 03-14-2022, 03:21 PM

in a victory for “occam’s razor”……i had some 2/0 cable laying around…side note:THIS is precisely why i tell my wife that i am such a pack rat.you never know when you might need something!

i thought to myself..maybe the cable is bad somehow. so i soldered on a couple of lugs and BINGO…everything works now. i ran it up to 2300 watts with no gripes from the inverter or excess heat from the cables(not even warm). the battery monitor didn’t love it, though. what’s that funny smell? oh crap…the shunt is smoking!!! i’m going to put in a renogy 500amp meter vs the crappy 15 dollar amazon one. $75 well spent, i hope.

moral of the story…crappy cables are just that…crap. DO NOT spend hundreds of dollars on a lithium battery(weize 100ah) and a beefy name brand inverter(renogy 3000w) and then be stupid and try to save $20 on cables.

i’m like you GHen…i have no intention of running a 3000w inverter flat out for any period of time..it was the best bang for the buck and gave me a bit of room to grow when i rob ANOTHER

bank to buy more lithium batteries to increase my time off grid.

one thing that does still bug me a bit about this 3000w beast is that the standby draw of about 2 amps seems excessive. maybe not..but it “feels” kinda high for a no load draw

GHen · 03-14-2022, 05:36 PM

Glad you got it figured out!

Just got turn it on and off as needed, that 2 amps will add up.

I’m hoping my system works better than my tests. That 75ah battery bench battery only has about 23ah usable, my rv should have closer to 200ah usable with my four 6volts. Might begin to add Lithium as a second battery bank next year as Prices continue to drop. Bringing my rv home next week for the install.

snoobler · 03-14-2022, 08:37 PM

Quote:

Originally Posted by jvincenzo

in a victory for “occam’s razor”……i had some 2/0 cable laying around…side note:THIS is precisely why i tell my wife that i am such a pack rat.you never know when you might need something!

i thought to myself..maybe the cable is bad somehow. so i soldered on a couple of lugs and BINGO…everything works now. i ran it up to 2300 watts with no gripes from the inverter or excess heat from the cables(not even warm). the battery monitor didn’t love it, though. what’s that funny smell? oh crap…the shunt is smoking!!! i’m going to put in a renogy 500amp meter vs the crappy 15 dollar amazon one. $75 well spent, i hope.

moral of the story…crappy cables are just that…crap. DO NOT spend hundreds of dollars on a lithium battery(weize 100ah) and a beefy name brand inverter(renogy 3000w) and then be stupid and try to save $20 on cables.

i’m like you GHen…i have no intention of running a 3000w inverter flat out for any period of time..it was the best bang for the buck and gave me a bit of room to grow when i rob ANOTHER

bank to buy more lithium batteries to increase my time off grid.

one thing that does still bug me a bit about this 3000w beast is that the standby draw of about 2 amps seems excessive. maybe not..but it “feels” kinda high for a no load draw

Glad you got it sorted. Some comments: Weize is not a premium brand, and while Renogy is prolific and recognizable, it is not "name brand." It's just re-branded cheap Chinese stuff with customer support slightly better than someone off alibaba.

24W idle draw on a low-end inverter is excellent.

jxnbbl · 03-15-2022, 04:11 AM

Interesting enough, from responses in the forum, although many don't go to 2/0. I went with the 2000W Xantrex Freedom inverter. It isn't installed yet due to shortages of certain simple parts, one being the 2/0 welders cable I wanted. Anyways here is the chart from this inverter (for all their models). Remember, that when wiring up multiple batteries, the jumper cables have to be made from this same gauge wire.

GHen · 03-15-2022, 06:55 AM

2/0 cables should be available everywhere. Check first at most welding gas supplies in town, they may only have black in stock but you can mark them with red tape. Second good source is from car audio installers. Some large auto parts stores should also sell it by the foot. Just watch for Copper clad aluminum wire found in cheap jumper cables, harbor freight stuff is in most cases aluminum.

I bought my 4/0 cables from an Amazon supplier for the connection to the inverter and 2/0 between the batteries.

jxnbbl · 03-16-2022, 09:25 AM

Quote:

Originally Posted by GHen

2/0 cables should be available everywhere. Check first at most welding gas supplies in town, they may only have black in stock but you can mark them with red tape. ...

You would think...

Probably more to do with where I live or the timing in the supply chain crap over the past year. First it was the wire and secondly it was the specific lugs I ordered (something like didn't have 3/8th holes but 1/4" holes. Anyways I check everywhere and then had to go to an electrical supply place and their distributor was the bottleneck. Everything is now here in a box ready for install.

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