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Small Cabin Forum / Off-Grid Living / Inverter Kaputnik
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gcrank1
Member
# Posted: 27 Jul 2022 22:14 - Edited by: gcrank1
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When my old, tired agm's didnt really have any beans left the cheapie 1000W 'psw' inv. would shut down.
I got another year out of them by pulling the worst battery out of the bank (load tested bad), going to a smaller inverter and not using energy hogs.
When I was down to one agm bat, I paralleled in a big old car bat (850cca?) thinking it might dump some big amps quick to start stuff; seemed to work. Then the agm faded and I replaced it with a seemingly decent used 100Ah 'marine dc'. That got me through last year....then last winter I bought into LFP; 2x 100Ah 12v (I was going to have to spend some serious bucks anyway on new LA so I threw the money at the LFP's)
Whadadiff!
All that to say....when the bats loose enough beans they wont run stuff with a start up load. Just like when a LA starting battery reads good voltage but wont turn the car engine over enough to start.

paulz
Member
# Posted: 27 Jul 2022 22:27
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This one handles the startup. The three things I've been trying to run, toaster, micro and coffee maker, all draw about 1500w and all run for about one minute before the inverter shuts down. The display says around 22 degrees C, manual says it shuts down at 60.

My 500ah of LFP have been hovering around 13.4, plenty of juice there.

ICC
Member
# Posted: 27 Jul 2022 22:49 - Edited by: ICC
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Quoting: paulz
My 500ah of LFP have been hovering around 13.4, plenty of juice there


The LFP could be able to do that, I am guessing. FWIW, 1500 watts at 12 volts is 1500/12 = 125 amps, and that is w/o allowing for whatever inefficiency factor the inverter introduces. If 10% the amps jump to 135 or so. If 20% then even more amps. Good LFP may very likely be able to handle that rate of discharge. But, being used who knows?

{EDIT... I found a valence datasheet that states max comtinuous load is 150 amps (on good batteries I assume). 300 amps for 30 seconds. }

What happens to the voltage reading on the battery when that inverter load is applied? If the voltage drops below 12 volts the amps drawn increase to try and make the watts. That becomes a rapid downward spiral.

Not saying that is the case. It could be a possibilty though.

ICC
Member
# Posted: 27 Jul 2022 23:38 - Edited by: ICC
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A passing thought.... I don't trust voltmeters on equipment until I verify them by comparing readings to those from a known good reliable meter. Especially meters built into cheap equipment.

If the graphical display drops significantly but the numerical readout does not, it would seem logical to think one of the two is incorrect, would it not?

ICC
Member
# Posted: 27 Jul 2022 23:54
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Quoting: paulz
From the battery bank I have 6awg cables, about 4', with a Victron low voltage cutoff set at 12.5 and a 50 amp breaker in the circuit


Hmmmm?

6 AWG wire may not be up to the task. But I don't havemy PC with me so cannot run numbers through the rlectrical calculator and I struggle with finding that info poking at s 6" screen with a finger.

Was that 50 amp breaker a mistype? Maybe 150 amp?

paulz
Member
# Posted: 28 Jul 2022 11:21 - Edited by: paulz
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Thanks ICC. Tried it again this morning, paying more attention. Under 1,460W load, the inverter V reading drops down to 11.3 at the point where it shuts off. Meanwhile, the SCC meter reads 13.0 and the Drok meter reads 12.2. It's all wired up as in the diagram below. So maybe a test with larger cables direct to batteries is in order. I still don't know why the inverter doesn't sound an alarm like it says it should.

My Valence batts are rated at 150A continuous draw, and I have 4 working. I could also take it outside and hook it to the truck with the motor running.

Also the Victron is 100A, I think the Drok is only 50
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paulz
Member
# Posted: 28 Jul 2022 14:53 - Edited by: paulz
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Well, you guys called it. I added a second set of cables, ran the nuker at 1,550, no problem. Voltage at the inverter stayed at 13.

Not out of the woods yet though. I added the extra cables direct from batteries to inverter, bypassing the Victron, Drok and breaker. To keep them in the circuit I would need larger cables for those legs in addition to the inverter cables. Or perhaps it's one of those causing the resistance. Or I could just go direct from bat to inverter.

Anyway thanks again guys, good thing I didn't send it back.

Nobadays
Member
# Posted: 28 Jul 2022 15:05
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At least you found your problem. It looks like 1/0 cable will handle 150amps, a little more than you will likely pull. Fine stranded copper is best.

paulz
Member
# Posted: 28 Jul 2022 16:51 - Edited by: paulz
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Yep, at least I found out it's not then inverter I been cussin at.

I have some 1/0 I think cable, and the connectors and hydraulic crimper. More to follow..

What prompted revisiting this, as I don't use the toaster or microwave much, was bringing out the 45 cup electric coffee maker from the city to keep up with my wife's insatiable thirst, the 1 quart propane French press just won't keep up. Me, I'm one cup in the morning and off to work.

paulz
Member
# Posted: 28 Jul 2022 18:30
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Good day for this, too tired to work on the roof.. So, I replaced the bat + to voltage protector and protector to circuit breaker with 1/0, about a foot each. The old cables were premade auto battery cables, marked 4G but I could feel them getting warm. Left the double 6awg cables to the inverter. Microwave test, inverter now showing 12.8 and shut off halfway through the 2 minute test. Hmm.

Next I removed the circuit breaker, 100W Ebay cheapo, and it passed the 2 minute test, inverter voltage at 13. So it looks like this breaker is part of the problem. Lastly I removed one of the double cables to the inverter, it also passed the test, voltage 12.9. So for now I'll just bypass the breaker.

No new 12v equipment for me, time to start changing over.
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ICC
Member
# Posted: 28 Jul 2022 21:02
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For breakers I find the best DC rated breakers are those sold by Midnite Solar. Some are DC only, some are AC or DC. All tend to be a bit pricey but they are very very good. They do need to be mounted in an approved case to meet code. For non-inspected installations as long as they are safely installed a container/case/cabinet could be improvised. Most, maybe al, are DIN rail mounting types and DIN rails are available from many sources.

paulz
Member
# Posted: 29 Jul 2022 10:37 - Edited by: paulz
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This morning I ran the coffee maker for 10 minutes at 1,550W. Inverter handled it no problem but my batteries felt it after watching TV last night plus the usual draws. They'll recover today but I doubt I would get away with it in winter. Probably need to go back to propane fueled coffee. I did toast my morning bagel no problem though..

I know I should have a breaker back in the circuit. All of the car/RV type inverters like this never mention it in the instructions, maybe they figure it's a given.

One minor annoyance is the inverter fan kicking on with a substantial load (not the TV) and it's pretty loud in a 300sf cabin. Can't hear the wife's jabbering over it, maybe that's not so bad..

gcrank1
Member
# Posted: 29 Jul 2022 10:58
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Iirc, Blue Sky stuff is highly regarded, too?
Those type of cheap CB's are only good as a quick disconnect (if that), not to be relied upon to 'break' under the supposed trip amps and known to bridge (right term?) internally sometimes when they do (BAD thing).
LOTs of info And the right stuff recommended over at 'diysolarforum.com).
You dont have to join up to read the posts.

ICC
Member
# Posted: 29 Jul 2022 16:35
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Quoting: gcrank1
cheap CB's are only good as a quick disconnect


Not even as that if they introduce sufficient resistance into the line to cause a voltage drop.

paulz
Member
# Posted: 29 Jul 2022 16:56
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The cable attachment studs on both the inverter and the breaker are only 6mm. And the cables that came with the inverter are also whimpy, not marked but smaller than they should be.

ICC
Member
# Posted: 29 Jul 2022 16:57
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I use 2 Midnite breakers on each charge controller; one on the input from PV and the other on the + line to the batteries. That makes it super easy to disconnect and reconnect if needed for maintenance or whatever. No tools are needed.

Plus a breaker on every + line coming off the batteries; inverter, DC well pump, etc. I do not like fuses for 2 reasons. Keeping track of spares can be a problem. Pulling a fuse to break a DC circuit that does have a load can result in a big arc flash that can actually burn you or start a fire. There is a youtube video that shows a very impressive flame arcing as a cartridge fuse was pulled.

gcrank1
Member
# Posted: 30 Jul 2022 20:40
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Correction:
It is 'Blue Sea' stuff that is highly regarded for elec for marine use. Makes it great for landlubbers too.

ICC
Member
# Posted: 30 Jul 2022 21:40
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That is very good marine equipment with an impressive lifetime "if not happy, return it for full refund or replacement" warranty and worldwide service, which can be important in the marine world. The biggest downfall when it comes to uses on land is that it is not approved under the NEC. But if that is not of concern Blue Sea is excellent, and there is no comparison the any of the off-name imported brands. My bus has a few Blue Sea components.

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