Solar Panels Amps

[Feral]

For the Solar Panel Guru's out there. I'm doing final set ups on the van I rebuilt. I needed to know if my current set up would manage the fridge I bought. A 60l dual zone Brass Monkey ( https://www.roadtechmarine.com.au/60l-brass-monkey-dual-zone-fridge-freezer/p/GH1644 ).

My set up at the moment is a Powertech MP3735 MPPT Controller, A 200w semi flexible Solar panel rated at 18 volt and 11.1 amps max permanently fixed to the roof and a 140ah gel cell 6 months old. Loaded the fridge up with bottled water and ran it on 240 volt till the water on the freezer side was frozen solid then switched over to12v. It is Northerly November here in the bay so clear hot days, one morning it did drizzle a bit but that was gone by 8 am And that was the morning the battery was dead. Approx 48hrs. I knew the panel would not keep up but by my uneducated math it should of last 7 to 8 days. Due to work the only readings i've been able to get was this afternoon. I got one of those amp load dohicky thingys. So at 3pm I got 17.6v going in at 2.21 amps. Didn't really alter to much over 30 minutes. Further readings will be getting done when I can.

The Powertech controller's tech info is Array size 360w @ 12v, Max input current 30Adc, Max input open cicuit voltage 65Vdc,
Question is, If the panel is not going to put out it's rated amps, remembering it's a 200w panel and I have a 160w fold up on the way =360w and this does not work, can I exceed the Array size so long as I keep the Amps and OCV under The max Ratings?

Or is this a real dumb A question?

 

[bicter]

No question is dumb.
The answer is that it shouldnt cause a failure and the controller will only deliver its rated current maximum.
One thing that will assist you is to get an inline wattmeter same as that Nightjar has purchased(discussed in another thread, https://www.prospectingaustralia.com/forum/viewtopic.php?id=31974&p=9 ). This will enable you to determine the amphours being provided into the battery, and also to measure power used by fridge, to determine if your system is sized correctly.
One thing that you may have missed in your calculation is the number of sun hours available in your location. Also check that your solar panel isnt being shaded by a branch or from an aerial on roof.

 

[mudgee hunter]

I think that's where the morphis? Pannels exceed on the average, better with shaded areas, bad angle and overcast days etc.

 

[Feral]

The dohicky thingy, chick speak for watt meter. couldn't remember what it was called. Panel on the roof has no shade and there is no angle to speak of. Battery is almost charged back t full so will be able to switch the fridge back onto 12v this week end and test further. Have a 260w pane in the shed I was thinking of plugging in. It was on the roof nut was to heavy for the pop top springs.

The fiddly stuff is taking forever to sort :8

 

[Feral]

Controller is showing float charge this morning so plugged the fridge back in to 12v. Watt meter between panel and controller, Hopefully will have some numbers to look over this afternoon after work

 

[bicter]

Hi,
I apologize, I should learn to read posts more thoroughly. :argh: :argh: :argh:

When you say the battery was dead, the fridge has a 3-stage low voltage battery protection so it is probable the battery wasn't dead and that the low voltage drop out switched the fridge off. By default, this cutout is set to high. Unfortunately it doesn't state what that voltage is.
Details on changing this setting is in page 6 of the manual.

Hope this makes sense.

 

[BigWave]

Hi Feral,

I'd say there's something amiss with your 200W panel or MPPT controller.

At 3pm, the sun is off zenith by ~45deg, so you should ideally be getting around 70% of max power or 140W. More realistically, probably ~120W.

Your panel was only delivering 39W, so unless the battery was nearly charged and the controller had backed off, then it seems something is amiss with the panel or controller.

Your current set-up should be capable of producing up to around 80Ah over a full cloudless day.
Given that you should never draw more than 50% from your battery (70Ah), it should be fully charged daily (with full sun) if your fridge draws less than 70Ah daily (~2.9A average continuous).

Given that the specified average daily power consumption for your fridge is 200W (let's say 400W daily in your area and for a very cold fridge temp setting), this is an average current of around 1.3A (i.e.:400/(12.6*24), so you should have ample margin with your current set-up (i.e.: 400/12.6 = 32Ah).
Reckon you should put wattmeters on the input and output of the MPPT (when the battery is not fully charged) to really see what is going on.
Also, measure the average daily power drawn by your fridge to get the complete picture.

If you suspect the panel, then temporarily hook it directly to your partially charged battery and measure the charging power.
The battery will likely be around 13.5V and, say the panel is expected to deliver around 160W (at noon) at this voltage, that means you should expect >10A.
Remember to disconnect the panel from the battery before it is fully charged!!!!!

 

[Jaros]

Why is that so: "Remember to disconnect the panel from the battery before it is fully charged!!!"

 

[BigWave]

After the absorption phase of charging, a lower float voltage is supplied by chargers to avoid overcharging.

Using a solar panel directly connected to a battery means excessive current will flow into the battery after reaching full charge, causing decomposition of water in the electrolyte and premature aging.

At high rates of overcharge a battery will progressively heat up. As it gets hotter, it will accept more current, heating up even further. This is called thermal runaway and it can destroy a battery in as little as a few hours.

Here's another take just using a small panel (12W) on a large battery bank:

https://www.youtube.com/watch?v=z5RtZe9AW2E

 

[Jaros]

Good video. I have a MPPT controller being fed from a 60W fixed solar panel on the roof rack wired to the battery.

 

[Feral]

Just got home from work so took a pic of the controller and the watt meter. First is the controller with the amps that's being used both by the fridge and battery.

Second is the watt meter. Now if I'm reading this right it's only delivering 3.49A, 16.21 volts and 56.5 watts average since plugging in at 6 this morning. The sun doesn't fully hit the panel till after 7. It's been a clear and hot sunny day. No clouds at all.

When the fridge is off, 2.9A is the charge into the battery which is correct for absorption charge according to the controllers destructions. With the fridge on the panel is not supplying enough Amps to cover fridge let alone top the battery up. Am I correct??

Me thinks the Panel has had the richard. Still going to wire in the other panel and see what that one does.

Edit was upside down images

 

[Feral]

Bicter, battery was reading 11.4 volts so not much left in there. BigWave, by the time i got home the battery was reading 12.8 /.9. It was at 13.5 this morning with float charge

 

[Ded Driver]

Feral, does your fridge cycle on & off correctly during the day. Might pay to check it too

 

[BigWave]

Hi Feral,
The reading of 56.5W is the power being delivered at the time of measurement - not the daily average. (i.e.: 16.21 * 3.49 = 56.5W).
A reading of 12.8/9V for a Gel battery under O/C or a small load load means the battery is fully charged:

So today, your solar panel has more than kept up with the fridge draw.
Your power input to the controller today has been 428W, so at around 90% efficient, that means that around 385W have been used to compensate for fridge draw (way higher than the fridge's specs state, so it's probably very hot out your way and you have your fridge on a cold setting).
Your MPPT seems to be running OK, with 56.5W input and 12.8*4.2A output (53.76W) i.e.: 95% efficiency - very good.
Let's see what it is tomorrow at dawn (battery will likely be down to ~ 12.5V in the morning [IMHO]), then again at sundown hopefully back to 12.85V with a nice sunny day.
PS: I'd also try that wattmeter measuring the fridge's power draw for a day. Thinking it may now be around 600-700Wh?
PPS: wishing we could get some nice sunny days down here, with hail and max temps of 14C

 

[grubstake]

Feral, does your fridge cycle on & off correctly during the day. Might pay to check it too

It's a big, cheap fridge/freezer with an under-sized, low voltage compressor (just 45W according to the specs). Methinks it's going to be On a lot more than Off - probably churning its tiny guts out non-stop!

Ridge Runner's post covers this issue in detail: https://www.prospectingaustralia.com/forum/viewtopic.php?pid=510782#p510782

Here is the Brass Monkey datasheet, which includes High/Medium/Low cut-out voltage details:
https://www.prospectingaustralia.com/forum/doc/member-docs/4012/1573196053_brass_monkey_gh1644-datasheetmain.pdf

 

[BigWave]

Seems like you're right grubstake - I'd say the fridge is on way more than off and drawing much more Ah than its specs state, but Feral is way up North, so that may be expected?
Still, I've also read some good reviews........

 

[Feral]

Up here in sunny Hervey Bay. Hot Northerlies blow just about non stop, or so it feels, here in November. Not what you would call hot hot at the moment, only got to 28 today. Fridge does cycle on and off. Have seen the amp draw drop off and climb on the controller and have heard it as well. I am running the freezer section as well. Might have to rethink Christmas lunch. Tomorrows job, among many others, will be to put a couple of Anderson plugs on the lead of the fridge.

Read RR's topic, sorta stuck with the fridge now, need to make it work. Thanks BigWave on the chart, it seems to me though that the panel is covering the fridges needs just. The battery ending up at 11.4v after 2 days has got me stumped

 

[Feral]

Sorry for taking so long to get back on, been a bit busy. Going to put another panel om the roof. With the 2 panels hooked up there is ample amps to both fully charge the battery and run the fridge. Special thanks to bicter for the instructions :Y: . Second panel will be mounted this way. Thanks to all for the help and info.

One day might be able to spring for a good 12v fridge but this will do to start with