Simple solar to assist with fridge while parked

[e9999]

yes, the second one is probably going to last longer in that it has exterior wiring between the 2 sides, so, easy to fix if the cables were to break (also much less likely than with interior ones). And also probably physically stronger (aluminum, glass etc). You can also likely separate the 2 sides easily by removing hinges and putting in a new connector if need be, so more versatile, if you can get by with only 75W for something, for example. But will take more space to store and be more unwieldy. You can also probably attach the second one to the roof permanently.

I would suggest to do some tests and trials outside the truck first, it would not be surprising that a cheapo controller would overcharge a battery, with potentially very "hot" consequences if lithium. And it is a PWM, not an MPPT controller, so less efficient, and I suspect with limited settings. But, eh, those are not Victron prices either!

 

[TXSunDevil]

I am going to put the alligator clips across the battery. Ill check the output under load and without a load when they arrive

 

[peesalot]

Just a mention - it is NOT good to connect a solar panel of more than say 15watts direct to batt without a controller, and IMO, even with a small panel a cont trickle could overheat/overgcharge batt.

 

[TXSunDevil]

Copy, this package has a controller that I will put in between the panel and battery

 

[e9999]

if a lead acid battery especially, you may want to make sure that your controller can go into actual float mode. Remember that PWM controllers are basically just on/off switches and do not have a full DC to DC converter like the MPPT ones.

 

[peesalot]

E - current flow wise, what is the diff between a PWM on/off and a float mode ? I assume a float charge kicks in sooner than the on/ off which basically lets the solar assist the load before batt drops to whatever voltage the PWM would kick in thereby keeping the batt closer to ideal voltage vs. a drain/refill cycle.

 

[e9999]

AFAIU (did some experiments but not 100% sure I recall this correctly):
a PWM controller switch will at first be on full time when the battery has low voltage, say 12V, for max averaged current. Picture that as the controller being a solid wire so to speak. [And the panel will then also be at that low voltage, 12V, so bad for panel efficiency]. Then as the battery voltage goes up and gets closer to absorption or the desired value (say around 14.4V), at some point it starts going on / off many times per second (that's the PWModulation part), with the off periods getting longer and longer as time goes by and the voltage gets higher. Note that at that point the panel is now also at a higher voltage (14.4V) so better for efficiency but still not close to the MPP (around 18V) for most "12V" panels, unfortunately. When it is at absorption (14.4), the off periods will be the longest so far, with comparatively little current, and the average of the on / off being the desired current for the desired voltage. Then, depending on the programming it may stay there or go float (say 13.5 for lead acid) and the switch on/off ratio will adjust accordingly. So, basically it's just a switch that goes on/off very quickly in varying ratio depending on need. But there is no independent control of battery and panel voltages since there no DC to DC converter, so the panel and battery are always at the same voltage during the on periods, and you will likely never get close to the MPP. And that's also why you definitely don't want to use a PWM controller with panels in series unless the panels and battery match well, because the efficiency will be worse still since your panels may then be at extremely low voltage (like 7V in the case of two 18V MPP panels in series and a 12V battery for ex) with terrible panel efficiency, much worse than if they are in parallel.

That's kind of how I view PWMs, and may be wrong at that, but my comment above was about making sure that the controller in question would be set up (and able) to go to float with a lead acid battery to avoid staying at absorption voltage, which is not good. That may not be a given for a cheap PWM controller (but I have no idea what this specific one can do).

 

[TXSunDevil]

My top of the line high quality kit arrived today It was heavier than I anticipated. The 6 year old Chinese boy that wrote the manual did a decent job. The float was set at 14.4V and it was default set for a maintenance free battery. I verified with my multimeter. I am not sure how to install the controller indoors as recommended, but ill do my best. I am heading to Cruisers in the Rockies this weekend so I will probably bring it along. Thing is I will probably be driving enough that I will not need it.

 

[e9999]

^ what do you mean the float was set to 14.4V? That is not a float voltage for lead acid, float should be around 13.5V. 14.4V is absorption voltage.

But what are you measuring there? Is that the voltage straight off the controller without a battery?

 

[TXSunDevil]

That was across alligator clips on battery output

 

[e9999]

well, that looks like they have the absorption ("booster") voltage set to 14.4V, that is fine for lead acid.
And the float to 13.7V, also fine.
And it looks like it can be changed, good.

 

[GeoRoss]

Don’t regret the PWM charge controller. That is what I used with my first solar set up and it worked great. I upgraded my system when I fell across a super deal. My first set up was only a solar generator. I’d run the fridge off the starting battery until I got to camp and switched over to the house AGM that would be recharged with a 100W panel and a PWM charge controller.

 

[e9999]

It's not so much that the PWM controllers are not worth having in the absolute, it's that the MPPT ones are just much better (more power, more versatile, etc). But the latter are also more expensive so it's a judgement call, of course. Conceivably, if space is no limitation, you could buy a cheaper PWM controller and an extra or bigger panel and come out about as well as with an MPPT controller and fewer panels. But there are also situations where PWM controllers are just not suitable for the job.
Anyway, it makes sense to start with a PWM controller if funds are tight, then keeping it as a backup or supplement when upgrading later to an MPPT.

 

[GeoRoss]

It's not so much that the PWM controllers are not worth having in the absolute, it's that the MPPT ones are just much better (more power, more versatile, etc). But the latter are also more expensive so it's a judgement call, of course. Conceivably, if space is no limitation, you could buy a cheaper PWM controller and an extra or bigger panel and come out about as well as with an MPPT controller and fewer panels. But there are also situations where PWM controllers are just not suitable for the job.
Anyway, it makes sense to start with a PWM controller if funds are tight, then keeping it as a backup or supplement when upgrading later to an MPPT.

Since I was dipping my toes into the whole “fridge/battery” thing, I was counting my pennies. The $75 SunSaver was much less expensive than the DC-DC charger with MPPT that I use now. The funny thing is I really don’t need solar much any more. My 100Ah lithium will run everything I need for about 9-10 days in temps below 85ºF. I can drive for 60-90 minutes and go from 50% to 100%.