Is this a normal voltage drop under load?

jrumohr1899

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System is 2x100Ah 12v AGM batteries (bought new 2 years ago, stored unused properly/regularly trickle charged but not constant, only installed in the camp trailer last week), 2000W Renogy inverter.

Under a rather heavy load (hairdryer), pulling 1300W, voltage on the batteries drops from 13.6 down to 10.9v, which signals an alarm on the inverter, but doesn't cut out. I'm guessing this isn't normal?

I'm also guessing I need to re-do some of my cables. I made a beginner mistake - soldered (poorly/lots of oxidation now I know better) some of the terminals, I think including the battery to inverter ones. Though the inverter cables I think are WAY oversized (4/0AWG), but there's still probably so much oxidation in there, that re-doing them with proper crimps might fix the problem.

IF my poor solder job on the cables is the culprit - is this likely to cause issues to 'normal' draws, say 1-15A (drawn from the battery) and causing lost power or is it mostly an issue under higher loads? I mean of course it seems to be a problem under load, and I assume that would be from my oxidized terminal connections, but what I don't know is if my system is just undersized for my inverter (haven't tested trying to draw 2000W) and the big voltage drops are to be expected or if this is not normal at all and it's likely all due to my cabling issue.
 

Don B. Cilly

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Well, if you measure the voltage directly at the battery, and it drops a lot less, there's your answer.
And if you suspect bad connections, why not re-do them anyway?
With something as "weak" as 12V especially...
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Bud Martin

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1300W on the AC output of the inverter means the power draw from battery will be about 1300W/0.85 = 1529W, current draw from battery at 12V will be 1529W/12V = 127A.
Can we see the pictures of your setup? it may be due to poor connections, poor quality circuit breakers/fuse, weak batteries, etc.
 

jrumohr1899

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1300W on the AC output of the inverter means the power draw from battery will be about 1300W/0.85 = 1529W, current draw from battery at 12V will be 1529W/12V = 127A.
Can we see the pictures of your setup? it may be due to poor connections, poor quality circuit breakers/fuse, weak batteries, etc.
Ah - okay - thank you. I keep getting my math confused. It's more draw than I had calculated. Today I found a new math that confuses me less for calculating amp draw from the battery - AC watts divided by 10. So 1300W/10=130A draw from the battery. It's a bit more conservative which is always good, but way easier for my brain to remember.

I'm going to re-do or re-check the connections. For some reason I had it in my head that "soldered is better than crimped" but I've since learned otherwise. And it was a pretty bad (lots of oxidation) solder at that.

What I'm gathering from the replies so far is perhaps my voltage drop isn't exactly normal. Other than those poor solder connections (only two I think), all cables are commercially made and very thick, I know between batteries it's either 4/0 or 2/0 from bank to inverter it's 4/0. Which I believe is overkill, but I went conservative since I've not done this sort of thing before.
 

jrumohr1899

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Well, if you measure the voltage directly at the battery, and it drops a lot less, there's your answer.
And if you suspect bad connections, why not re-do them anyway?
With something as "weak" as 12V especially...
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I'm getting the battery voltage readings from the charge controller (Renogy 30A Rover), hard to get probes into where the batteries are. But yes, I'm going to re-check and re-do the cabling to rule that issue out.

What I'm gathering is that perhaps this big of a voltage drop isn't exactly normal, hence the replies to check and fix things. Thank you.
 

Bud Martin

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Ah - okay - thank you. I keep getting my math confused. It's more draw than I had calculated. Today I found a new math that confuses me less for calculating amp draw from the battery - AC watts divided by 10. So 1300W/10=130A draw from the battery. It's a bit more conservative which is always good, but way easier for my brain to remember.

I'm going to re-do or re-check the connections. For some reason I had it in my head that "soldered is better than crimped" but I've since learned otherwise. And it was a pretty bad (lots of oxidation) solder at that.

What I'm gathering from the replies so far is perhaps my voltage drop isn't exactly normal. Other than those poor solder connections (only two I think), all cables are commercially made and very thick, I know between batteries it's either 4/0 or 2/0 from bank to inverter it's 4/0. Which I believe is overkill, but I went conservative since I've not done this sort of thing before.
You have to factor in the inverter efficiency, 85% is typical, 10V is good to use for calculation too for the low Voltage before inverter goes into low battery shutdown.
 

Don B. Cilly

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Well, I've never tried to draw ~150A from 200Ah batteries, so I wouldn't know how big a voltage drop to expect - especially from lead-acid - but if
you even vaguely suspect poor connections... think of the heat that could generate. Surely enough to melt you cables' insulation, with the obvious risks of that.

On another note, I don't have a hair dryer (I keep my hair very short) but, I have a hot air gun that, in middle setting (3 of 5) would burn my hair off if close enough and draws 500W.
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Substrate

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System is 2x100Ah 12v AGM batteries (bought new 2 years ago, stored unused properly/regularly trickle charged but not constant, only installed in the camp trailer last week), 2000W Renogy inverter.

There can be variables found here too (trickle chargers *can* kill good batts if not done right). Do you have a at least a 10 - 25a charger, (no need for higher with conventional 100ah agm unless you are running pure-lead) and can you charge each individually before trying to place them back into service?
 
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Tomthumb62

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Well, I've never tried to draw ~150A from 200Ah batteries, so I wouldn't know how big a voltage drop to expect - especially from lead-acid - but if
you even vaguely suspect poor connections... think of the heat that could generate. Surely enough to melt you cables' insulation, with the obvious risks of that.

On another note, I don't have a hair dryer (I keep my hair very short) but, I have a hot air gun that, in middle setting (3 of 5) would burn my hair off if close enough and draws 500W.
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Pulled the whole system apart and checked the inverter cables. As I suspected, where I soldered the cables are highly oxidized. Cable insulation looked fine. I had to cut off over an inch to get to somewhat clean wire. Then I did the salt+vinegar followed by a baking soda bath and that cleaned up the wire pretty well. Also found out the cables are 1AWG but a 2000w inverter should have 1/0, so I’ll be ordering some new cables soon. I crimped on new copper lugs, those things are about $5/ea now! I came up with a cheap clever way to crimp without special tools, I’ll make a new post about it lol.

Anyways it’s all hooked back up and I’ll stress test again tomorrow. I don’t expect to ever max out the inverter, but I figure it should be wired up for that should it ever happen.
 

Bud Martin

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Try running low load first and check the Voltage drops on the wires, circuit breakers, then increase the load and recheck the Vdrops to see what you get.
 

Tomthumb62

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Good news

Ran the hair dryer on low and then high, draws 1300w on high. Battery voltage dropped from 13.4 to 12.4, not bad! Took about 30 seconds to get to 12.4 and then hovered between 12.3 and 12.4. Same test yesterday before I fixed the inverter cables, it dropped to 10.8 and maybe would’ve dropped lower but I stopped the hairdryer at that point.

So it seems that cleaning up my oxidized cables has made a huge difference. Lessons can be learned many ways, but the hard way usually sticks lol. Could’ve been harder, like cables on fire. So grateful that didn’t happen.

I’ll still be replacing the 1AWG with 1/0AWG for the 2000w inverter, soon.
 

Tomthumb62

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Good idea. All connections have been checked regularly due to needing to dismantle it for upgrades, etc. except I have not checked the MC4 connections from the roof panels.

Which leads me to another question if you don’t mind. The roof panels are 2x100w in parallel. They always produce about 18v, but rarely more than 2-4A. Max amps should be about 10A. I’ve never seen them do that, usually very low amps. Now these are the flexible mono kind and of course aren’t angled ideally to the sun, but even in the peak of summer with the sun high overhead, I don’t get more than 5-6A. The new 200w suitcase we got, which we angle to the sun, produces 7-10A regularly.

Does this sound like par for the course? Or should I be expecting a bit better amp production? I’m near the 48th parallel north.
 

Bud Martin

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The panels do not push current into the load, I.E. Charge controller, batteries, inverter, the load will draw current as needed up to the max it can draw.
if the batteries are full and you have light loads then you will not see much current draw from panels. You can add more load and see if the current draw go up. 200W worth of panels you'll get about 75% from them will be typical.
What is the make and model of your charge controller?
Is it 20A or less Charge controller?
 

Tomthumb62

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The panels do not push current into the load, I.E. Charge controller, batteries, inverter, the load will draw current as needed up to the max it can draw.
if the batteries are full and you have light loads then you will not see much current draw from panels. You can add more load and see if the current draw go up. 200W worth of panels you'll get about 75% from them will be typical.
What is the make and model of your charge controller?
Is it 20A or less Charge controller?

The case in question is when the batteries were fairly discharged and the controller was bulk charging, so the load was real.

SCC is a Renogy Rover 30A.

I think it’s just our northern latitude combined with flat mounted panels. They get dirty easily but I do wash them regularly, but cleaning them doesn’t seem to improve output much.

Update to my test. I put a watt meter on the hairdryer, I’m getting 1600w draw now whereas yesterday with the bad cables, I only got 1300W. So 300W more draw AND only 1.0v drop, compared to 2.4v drop. Works for me.
 

jrumohr1899

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There can be variables found here too (trickle chargers *can* kill good batts if not done right). Do you have a at least a 10 - 25a charger, (no need for higher with conventional 100ah agm unless you are running pure-lead) and can you charge each individually before trying to place them back into service?
Yes, I have a NOCO Gen2 20A charger. It's a "smart" charger. It has four leads - 2 for each battery. I don't fully understand it, but it charges both batteries individually (at max 10A each) and since they are both connected I think it somehow knows that they are also connected in parallel.
 
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