Questions about trailer solar systems and charging off the tow vehicle, and shore power

[dwh]

All true. But the OP isn't going to use any of that advanced capability on this trailer.

As I said, depending on how much solar he has, he might want to upgrade the charge controller. Adding a battery monitor would be nice, but not really needed if he's just looking to keep the new batteries from cooking while the trailer is stored.

 

[Pastryslayer]

I caved and ordered the Iota and the BMV this morning. Supposedly they will arrive today via Amazon Prime, but for some reason the IQ4 comes Tuesday. DWH, I had since found the application specific IQ4 descriptions, but I appreciate the confirmation that I ordered the right one (FLA).

I may go for the Victron solar controller in the future but I think I'll let my wallet recover. We're going to the NW Overland Expo in June, that'll be the shakedown trip.

Side note: I finally got a decent look at the solar panel label. Its a Schott Perform Poly 235, which I gather is a 235 watt panel. Pretty big, in fact it's partially blocked by my RTT currently. Need to rig a slider of some kind for when we're stationary.

 

[dreadlocks]

consider making it portable, if ANY part of the panel is shaded its output will very tiny.. but yeah start taking it out and figuring out what you wanna upgrade/change based off your needs.. thats a nice sized panel and should do a good job at keeping you out longer as long as you can keep it in the sun..

 

[Pastryslayer]

Kinda of what I was thinking. It's bolted on right now. I thought about some kind of latch release/qd system and just position it where I want it. I don't think its terribly heavy.

 

[Pastryslayer]

While I wait I think I worked something out for myself...shocking, I know. Since the inverter has a 10 Amp charge limit, which is why we are abandoning it as a charger, would that mean that the AC power outlet is also limited to 10 Amps? With the shore power plugged in (no bank attached), I can plug my phone in and it charges. But when I plug in my electric kettle, nothing happens. The kettle is 1500W at 120 volts, so it should be a 12.5 Amp draw, right? Does that mean I need an inverter with more than 12.5 amps of output (presumably at least a 15 amp rating) to run the kettle or am I missing something else?

I don't necessarily need an electric kettle, although they are very convenient. Mostly it's a mental exercise.

 

[dreadlocks]

oh no.. its just got a 10A 12VDC power supply in it to back feed.

1500W is 1500W at 120v or at 12v.. at 120v its 12.5A, at 12v its 125A.. If your Inverter is putting out 1500W its outputting 12.5A @ 120V, but its drawing >125A from your 12VDC battery bank (more because inverters are not 100% efficient at converting DC to AC)..

Sounds like your 1500W inverter is not able to fire up your 1500W kettle, which honestly is not that surprising.. most kitchen appliances list their cooking output power, not input power.. for example my 800W Microwave draws 1000W from the outlet, because its cooking at 800W and its not that efficient at doing what it does so there's 200W lost to the ether..

 

[dwh]

Holy crap! That panel has a Vmp of 30v!!

Dude...you seriously need an MPPT controller. With a PWM the panel runs at battery voltage and running a 30v panel at like 14v is bloody inefficient.

Running an 18v panel at battery voltage with PWM is fine...somewhat inefficient...but not too bad. Even so, with 200w of solar, the inefficiency is enough to justify the expense of MPPT.

That's a panel made for a house, where you'd string a bunch together. That's not a bad thing, my 300w Astroenergy panel is the same and has a Vmp of 36v - but no way I'd try charging a 12v battery with a PWM with it...hell, I'd be lucky if I saw 200w max out of it on a good day.

 

[dreadlocks]

my 325W Panasonic does >60v.. definitely need a MPPT charger for house panels or your just going to see a fraction of the output on a 12VDC bank.. I didnt even think you could hookup that much voltage through a PWM w/out toasting it.

 

[Pastryslayer]

oh no.. its just got a 10A 12VDC power supply in it to back feed.

1500W is 1500W at 120v or at 12v.. at 120v its 12.5A, at 12v its 125A.. If your Inverter is putting out 1500W its outputting 12.5A @ 120V, but its drawing >125A from your 12VDC battery bank (more because inverters are not 100% efficient at converting DC to AC)..

Sounds like your 1500W inverter is not able to fire up your 1500W kettle, which honestly is not that surprising.. most kitchen appliances list their cooking output power, not input power.. for example my 800W Microwave draws 1000W from the outlet, because its cooking at 800W and its not that efficient at doing what it does so there's 200W lost to the ether..

Ah, ok. No hope at all for the kettle then. This inverter isn't going to be much help at all, I'd be better off plugging the kettle into the shore power outlet directly.

 

[dwh]

And we're abandoning the charge function of the inverter/charger because we don't know how it behaves voltage-wise. Don't know if it will cook batteries if left on long term.

But yea, we also know 10a ain't enough either.

 

[dreadlocks]

might try testing a smaller load on it and see if you can figure out its limit, alot of those cheap china inverters are not worth their weight and really struggle to meet their spec'd output.. might just take the thing out and forget about it.

a toaster is a nice AC load tester, they pull ~1000W usually..

Ive got a 1000W inverter, runs my microwave oven, coffee maker, toaster, crock pot, ice maker, and various battery chargers such laptops and cordless tools.. but but those high draw ones I specifically had to shop for low output ones.. my home coffee maker was 1500W but my portable travel maker is only 800W.. my microwave is made for dorm rooms and tiny, its like 700W

 

[Pastryslayer]

Holy crap! That panel has a Vmp of 30v!!

Dude...you seriously need an MPPT controller. With a PWM the panel runs at battery voltage and running a 30v panel at like 14v is bloody inefficient.

Running an 18v panel at battery voltage with PWM is fine...somewhat inefficient...but not too bad. Even so, with 200w of solar, the inefficiency is enough to justify the expense of MPPT.

That's a panel made for a house, where you'd string a bunch together. That's not a bad thing, my 300w Astroenergy panel is the same and has a Vmp of 36v - but no way I'd try charging a 12v battery with a PWM with it...hell, I'd be lucky if I saw 200w max out of it on a good day.

Aw man. Just when I thought I was making progress. If the panel puts out 30v how much of an mppt do I need? May as well go Victron so it can talk to the battery monitor...

 

[Pastryslayer]

might try testing a smaller load on it and see if you can figure out its limit, alot of those cheap china inverters are not worth their weight and really struggle to meet their spec'd output.. might just take the thing out and forget about it.

a toaster is a nice AC load tester, they pull ~1000W usually..

Ive got a 1000W inverter, runs my microwave oven, coffee maker, toaster, crock pot, ice maker, and various battery chargers such laptops and cordless tools.. but but those high draw ones I specifically had to shop for low output ones.. my home coffee maker was 1500W but my portable travel maker is only 800W.. my microwave is made for dorm rooms and tiny, its like 700W

I'll poke around for a lower power boiler, but I'm thinking an inverter upgrade is inevitable.

As for the PWM...maybe I did toast it. Although the lights still come on.

 

[dreadlocks]

install the BMV first and then after some testing and field runs you'll have a much better idea what you want.. that was like item #1 for me when I completely re-did all my trailer wiring... that data then drives your next purchasing decisions because now your not just guessing, you know.. you'll see how much solar is helping now, and if its not doing what it should.. then perhaps that becomes priority over inverter, etc.. but if its working okay and keeping you topped off then perhaps its priority of getting an upgrade goes down because you really wanna run that kettle.. If you find your self sitting w/shore power frequently and decide you need to take advantage of that then mebe the onboard charger takes priority.. everyone has their own styles and needs, its really difficult for us to give generic advice thats good for everyone in every situation.

that 235W panel is going to need a 20A charge controller if you want to see maximum output from it (235W/12V=19.58A).. the BMV will show you whats going into the battery, if your batteries are low and it cant get remotely close to that even when its sitting 100% direct sunlight then you know your getting robbed of solar efficiency.

 

[dwh]

Aw man. Just when I thought I was making progress. If the panel puts out 30v how much of an mppt do I need? May as well go Victron so it can talk to the battery monitor...

235w ÷ 11v = 21a
(Worst case scenario - dead battery, full solar)

A 20a should be plenty. You might lose an amp or two if the battery is dead and the sun is direct on the panel and the panel is at freezing temp...otherwise you'll never exceed the 20a limit.