A simple, inexpensive, yet powerful solar storage system

[NW-Bound]

I notice these are generally rated for 3 amps. Any idea what they really are - i.e. adequate for an iPad?

I don't know what current an iPad draws. Also, I thought 3A is about the max you can draw from a USB socket.

Higher power can be delivered by USB-C, and that is with a voltage higher than 5V.

 

[NW-Bound]

OK, perhaps you want a USB charger with QC 3.0 features. It would go up to 9V or 12V to provide more power, depending on the request from the device being charged.

Here's one for $3.49, free shipping, good for 24W as claimed. Note the big toroid inductor, compared to the small ferrite square inductor in the earlier one.

 

[youbet]

200W of panel is not much at all. I am surprised that it generates enough for the fridge full-time use.

The owner, a tech-savvy guy IMHO, told me he hasn't had a problem so far but has never tested it in a winter situation with long nights and short, overcast days.

My little 3-way fridge draws 10A when running on 12V and would never make it overnight, that's for sure. In fact, I worry about over-drawing the house battery if we're stopping for a long lunch, or some tourist stuff, and so switch it over to propane.

 

[NW-Bound]

The owner, a tech-savvy guy IMHO, told me he hasn't had a problem so far but has never tested it in a winter situation with long nights and short, overcast days.

My little 3-way fridge draws 10A when running on 12V and would never make it overnight, that's for sure. In fact, I worry about over-drawing the house battery if we're stopping for a long lunch, or some tourist stuff, and switch it to propane.

I have a 200W solar panel on my motorhome, and never dreamed of running the 2-way propane/120VAC ammonia absorption fridge on solar battery (via an inverter).

The 6-c.f. fridge draws more than 300W, and I don't think it ever gets cold enough to stop.

 

[youbet]

^^^^^

I guess the new high efficiency 12V compressors make these new fridges possible.

 

[NW-Bound]

Yes.

More than electric power or propane consumption, the ammonia absorption fridge cooling power is so weak, when the ambient temperature is high such as 90F, it can barely keep the interior temperature below 45F. We spent too much time worrying about food spoilage and had to keep eyes on the wireless thermometer all the time.

I figure that if we had an auxiliary portable 12V compressor fridge/freezer, we would open the main fridge less, and that should help it. It's easy to run this portable fridge off solar.

 

[Jerry1]

For USB charging, how about a cigarette socket like this, that can be bought for a few dollars to wire directly to the 12V battery?

You can then plug in a common cigarette-plug-to-USB adapter, also for a few bucks.

Just for kicks, I bought one of those cigarette adapters and made a little rig to connect it to my Ryobi 18V batteries. The USB adapter can handle up to the 18V the Ryobi’s put out. It’s nice to have the ability to plug in my phone and my Bluetooth speaker and I can keep the music going for several hours. And, if a battery does drain, I have about 6 more of them fully charged (unless I did yard work that day).

 

[Sunset]

OK, perhaps you want a USB charger with QC 3.0 features. It would go up to 9V or 12V to provide more power, depending on the request from the device being charged.

Here's one for $3.49, free shipping, good for 24W as claimed. Note the big toroid inductor, compared to the small ferrite square inductor in the earlier one.

Strangely when I see your latest posts, I don't see any image or link. But when I quote your post I see the image link. But it still does not show when I post this reply.

I did find this one at: https://www.ebay.com/itm/124450365960

It's all pretty interesting and amazing the little circuits available, and so cheap..

 

[travelover]

.........It's all pretty interesting and amazing the little circuits available, and so cheap..

I'm surprised at the free shipping. Since the international postal rules revision, shipping costs have really risen.

 

[skyking1]

the high efficiency Danfoss DC compressors make a lot of good options possible these days.
This fridge will run on around 800 Wh per day from solar and battery, no inverter needed. It would be great for a remote cabin setup, and a modest array and battery bank would cover the needs with high reliability. Taking the inverter out of the equation for when you are away takes away one layer of complexity/failure point.
https://www.defender.com/product.jsp?id=1770243
There are many DC fridge manufacturers out there with varying reviews. One of the worst is the Norcold brand. It seems that all the good reviewed units are built around the danfoss compressors.

 

[ERD50]

I'm surprised at the free shipping. Since the international postal rules revision, shipping costs have really risen.

I've wondered about that. There was a discussion a few years back about how these inter-country postal rates are set, and I guess the US made a deal when we were the ones shipping out? It supposedly cost less to ship from China to the US, than it did to ship across the street in the US.

I've seen shipping on these cheap Chinese places go up, but not dramatically (well, maybe %-wise, but still seems very cheap).

-ERD50

 

[NW-Bound]

I'm surprised at the free shipping. Since the international postal rules revision, shipping costs have really risen.

I've wondered about that. There was a discussion a few years back about how these inter-country postal rates are set, and I guess the US made a deal when we were the ones shipping out? It supposedly cost less to ship from China to the US, than it did to ship across the street in the US.

I've seen shipping on these cheap Chinese places go up, but not dramatically (well, maybe %-wise, but still seems very cheap).

-ERD50

No, it's not really free shipping for this particular item, or any item.

Other vendors show a lower price, but with some shipping added. The total is about the same.

And I have noticed the following with Chinese vendors. They use shipping consolidators who package a lot of these small items into a big box, then move them via airfreight or slow boat to CA.

In CA, they open up the box, and send the individual items via US Postal and pay only the domestic postage rate. The return addresses I have seen are all from California.

I guess it's still fair.

 

[braumeister]

It supposedly cost less to ship from China to the US, than it did to ship across the street in the US.

Random anecdote:
A friend was importing some things from China a few years ago and he said it cost something around $800 to ship a 40 foot container from China to the west coast. The container could contain anything; the shipping lines didn't care. So that's at least 20 pallets of stuff.

 

[NW-Bound]

the high efficiency Danfoss DC compressors make a lot of good options possible these days.
This fridge will run on around 800 Wh per day from solar and battery, no inverter needed. It would be great for a remote cabin setup, and a modest array and battery bank would cover the needs with high reliability. Taking the inverter out of the equation for when you are away takes away one layer of complexity/failure point.
https://www.defender.com/product.jsp?id=1770243
There are many DC fridge manufacturers out there with varying reviews. One of the worst is the Norcold brand. It seems that all the good reviewed units are built around the danfoss compressors.

+1 about the Danfoss compressor.

I don't see how the 12V upright fridges have to cost so much. The price is coming down but not fast enough, compared to the 12V portable chest freezers/ refrigerators.

I could buy 2 of the portable ones, and use one as a fridge with the other one as a freezer for my RV, and still save a lot of money.

 

[skyking1]

I agree the price is high, but worth it to me. The new RV will get that model above if they still make it. Indel Webasto is the leader in boat fridges and freezers. Having an RV with ~600W of fixed panels on it, not aimed, possibly partly shaded and being able to walk away without worrying about my food is quite handy. A pair of those batteries above in the thread would carry it over many cloudy bad days if I can manage the vampire loads.

 

[Sunset]

the high efficiency Danfoss DC compressors make a lot of good options possible these days.
This fridge will run on around 800 Wh per day from solar and battery, no inverter needed. It would be great for a remote cabin setup, and a modest array and battery bank would cover the needs with high reliability. Taking the inverter out of the equation for when you are away takes away one layer of complexity/failure point.
https://www.defender.com/product.jsp?id=1770243
There are many DC fridge manufacturers out there with varying reviews. One of the worst is the Norcold brand. It seems that all the good reviewed units are built around the danfoss compressors.

That is really great, as eliminating the inverter means not wasting a significant percentage of power just to convert it.

 

[Sunset]

My Panel[-]s[/-] arrived today from Amazon.
I told the delivery guy there should be 2 panels.
He said maybe it's on another truck, and marked it as delivered.

I call Amazon, but it's Sunday so only Bezo's is working Dreaming...

I get a bot phone call, no good, can't understand the issue with my order, so I do the chat thing.
The person offers me 3 options, one of which is a refund of 40% of the cost and I keep the 1 panel
I point out it's less than 1/2 the value, so the person chats the most they can offer is 43%
Seems we are playing "Lets make a Deal" ..

I say I'll take the free replacement order and return the 1 panel for free.
Now my accnt says I'm getting the free order on Wed, and will return the 2 panels on Wed

 

[NW-Bound]

I just came in from the patio out back, where I tested an inexpensive 2000W inverter that I bought off Amazon Warehouse Clearance.

Worked fine with a load of 1600W provided by two portable room heaters with setting of 400W/800W. It complained that the battery voltage was low when both heaters were cranked up for a total of 1600W. But the monster LFP battery voltage is not low. I guess that's a problem with inexpensive stuff. There's always something wrong.

Better inverters/chargers will let you program different settings to your liking.

The efficiency of this one at 1600 W is not bad though, and better than 90%.

I did some more tests with this inexpensive inverter. No, the plaintive beep the wretched thing emitted with the 1600W load was not because the voltage from my monster 28.8kW battery sags. Rather, it meant "I am getting overloaded, and will shut down soon". And it did if I let it go a bit longer.

Hah! So, that's why the earlier buyer returned it, and I was able to get it in near new condition from Amazon Clearance for $142. This makes sense now. 2000W my tush!

OK, the price is still good, and I was thinking about using it as a separate inverter for my water heater. When powered with 120V instead of 240V, the heater draws only 1kW instead of 4kW. It takes longer to run, but it's OK as we never ran out of hot water from the 50-gal WH since the kids moved out.

And this inverter has decent efficiency. They claim better than 90%, and I measured closer to 95%. And its idle power consumption is a respectable 6W.

I will keep it instead of sending it back, as it works for the planned usage. Detaching the WH from one of the MPP Solar inverters will allow the full 2400W power to the circuit the inverter is serving. I occasionally overload the inverter when I forget that the WH may happen be on at that instant.

 

[NW-Bound]

My Panel[-]s[/-] arrived today from Amazon.
I told the delivery guy there should be 2 panels.
He said maybe it's on another truck, and marked it as delivered.

I call Amazon, but it's Sunday so only Bezo's is working Dreaming...

I get a bot phone call, no good, can't understand the issue with my order, so I do the chat thing.
The person offers me 3 options, one of which is a refund of 40% of the cost and I keep the 1 panel
I point out it's less than 1/2 the value, so the person chats the most they can offer is 43%
Seems we are playing "Lets make a Deal" ..

I say I'll take the free replacement order and return the 1 panel for free.
Now my accnt says I'm getting the free order on Wed, and will return the 2 panels on Wed

Dang! I hate it when things get so screwed up. You have my sympathy.

PS. I am reminded of this mishap occuring to me. I bought a pair of rear shock absorbers for my vehicle. The order came as two long boxes taped together. One of them was empty! What the heck!

It was easy for me to prove one of the boxes was shipped empty instead of the content falling out during shipping. The shipping label showed the shipping weight, and it corresponded to 1 shock absorber.

After I sent photos to eBay to dispute, the vendor refunded 1/2 of the order. I ended up buying another single absorber elsewhere.

 

[skyking1]

It seems unnecessary to invert power to a resistive load like a water heater.

 

[travelover]

My Panel[-]s[/-] arrived today from Amazon.
I told the delivery guy there should be 2 panels.
He said maybe it's on another truck, and marked it as delivered.
.......

I ordered two trailer tires and they came on separate trucks ten minutes apart. Don't give up, probably on its way.

 

[NW-Bound]

It seems unnecessary to invert power to a resistive load like a water heater.

Ah hah! I am glad you brought this up.


First of all, you may not have the solar panels putting out the right voltage for the WH. If the panels are presented with a mismatched load, the obtained power is suboptimal. You will need something equivalent to an MPPT charger to take care of the mismatching.

Secondly, and this is UTMOST important.

You don't wire a string of solar panels to a WH. You would regret it soon!

Remember the arcing when you break a high-voltage DC circuit. When the water temperature reaches the set point, the thermostat clicks off. And the current will continue to flow through the arc, burning the thermostat and melting its contacts. A big mess, and possibly a fire.

There's a way to drive a resistive load with a DC high-voltage source. And that is by using an electronic switch, namely a MOSFET or IGBT transistor, and not a mechanical contact that will arc.

I was going to build this electronic switch, but kept dragging my feet. It will require careful testing to make sure things work as intended.

When I ran across this cheap inverter, decided to buy it for the water heater, and will use it for something else after I build the electronic switch, which will also have digital temperature control instead of a nebulous bimetallic contact.


PS. I forgot a 3rd reason. My WH is old, and has no electronics. New WHs like the one I had up in my 2nd home, and it is built in 2005, have electronics in its control circuit. It won't like DC voltage. I don't know how bad things can get, but it is certain not to work with DC.

 

[ERD50]

...

There's a way to drive a resistive load with a DC high-voltage source. And that is by using an electronic switch, namely a MOSFET or IGBT transistor, and not a mechanical contact that will arc.

I was going to build this electronic switch, but kept dragging my feet. It will require testing to make sure things work as intended. ...

Those are kind of a pain, and get expensive for high currents.

I built a couple controllers so I could adjust the duty cycle on some 1650W 120V heaters for my brewing set up (heat water, and bring ~ 7 Gallons to a boil).

The triacs have ~ 1~1.5V drop, so 13A is 13~19.5 Watts, and that's not a small amount of heat to get rid of. The high current units from a known source get pretty expensive, and the cheaper ali-express types are often rebadged with a higher capacity. Since the ali-express ones are so cheap, I doubled up, and had my controller alternate between the two, cutting their power dissipation in half, which gave me plenty of margin, the heatsinks I used ( ~ 3" finned cube) barely got warm.

And for the times that I need full power, I switch in a relay, to avoid wasting and heating the SSR.


Mosfets are resistive, so power loss can be as low as you want to afford.

I dunno, your inverter is a sunk cost, not sure I'd want to jump through too many hoops to knock a few points of efficiency loss from that load.

QUESTION: What do you plan to do when you move? While the cost savings is impressive, I think the tinkering aspect of monitoring it would drive a lot of people away. I'm being careful to keep my built in tinkering to a minimum and easily removable. You've got quite an investment there!

-ERD50

 

[travelover]

No, it's not really free shipping for this particular item, or any item.

Other vendors show a lower price, but with some shipping added. The total is about the same.

And I have noticed the following with Chinese vendors. They use shipping consolidators who package a lot of these small items into a big box, then move them via airfreight or slow boat to CA.

In CA, they open up the box, and send the individual items via US Postal and pay only the domestic postage rate. The return addresses I have seen are all from California.

I guess it's still fair.

True, but shipping from China used to be ridiculously inexpensive. I could order parts for $1 with free shipping. You couldn't even send a postcard to China for a buck. Now a lot of similar items have several dollar shipping.

 

[skyking1]

I think it is a worthy project for you, and any water heater with screw in elements can be retrofitted with simple thermostats and safety switches. High voltage DC is not common but both do-able and it increases efficiencies via smaller wire size and reduced currents and line loss.
I can think of no one better to experiment with it