More fun with Renogy MPPT and LFP

[Almot]

Toying with a new to me 12V compressor car fridge. Cheap Chinese box, LG compressor, 50L volume split ~28L fridge, 22L freezer. The goal was to see whether my added insulation made any difference: Reflectix taped around the box, and an ugly cover made of an old bed spread - it had some "fur" inside.

Fridge draws >34AH per 24 hrs at 75F ambient, though in defence of a cheap box I should say that the freezer bin is huge and set to -2F. Fridge set to 39F.

Fridge connects to Load terminals of Renogy,
Renogy connects to 12.8V 120AH LFP,
LFP connects to nothing, partially charged.

Busy with other things, I suddenly noticed that don't hear quiet "purr" of the fridge. MPPT is blinking "battery problem", voltage 11.

Renogy Load terminals were supposed to cut the load off at 12.6V, - they didn't.
Renogy Low-voltage alarm was supposed to sound at 12.7V, - it didn't.

Independently, darn ice box didn't cut off at 12V either - downstream from MPPT on a thin #18 cable it reads lower voltage, so LVD 12 is a-okay, only it didn't cut off.

Yeah, I know, buy Victron, I've been warned. Still curious whether I did something wrong, other than buying Renogy.

[Almot]

time2roll wrote:
If you are running into low voltage issues.... need more battery.

I wasn't interested to see how long the battery would last. It was testing of the load itself, the fridge. Battery wasn't half-full and there was no charging at any time.

What pissed me off was that Renogy allowed $600 battery to drop as low as 11V, rather than disconnecting the load at 12.6V as per Renogy settings.

Possible reason: confusing Chinglish of the app with no LVD but with "Discharge Limit" and "Over Discharge" instead, the former being a mystery and the latter (probably) an inept name for LVD. I thought that LVD was a "Discharge Limit" and set it at 12.6, but the LVD apparently was an "Over Discharge" (set below 12, don't remember now).

Also, settings in User-defined mode would revert back to defaults if I dial in a different battery type, ex. Gel or Flooded and then return it back to User-defined mode. If you do this, all User settings are lost - LVD would change to 11V, Boost time to 120 minutes and Temp Comp to 3C. Very dangerous. But, hey - who would ever change their battery, right?

[time2roll]

If you are running into low voltage issues.... need more battery.

[3_tons]

pianotuna wrote:
3 tons,

I'm not worried about meter drift. I'm interested in maximum number of cycles.

Either way, not much of a concern for me-septuagenarian, as the amount of LFP charge cycles will most likely far exceed the amount of sand remaining in my hour glass 🙂 !!

3 tons

[pianotuna]

3 tons,

I'm not worried about meter drift. I'm interested in maximum number of cycles.

[Almot]

pianotuna wrote:
The load terminals on my Blue Sky are used as a "sun sensor" switch. Perhaps yours are too?

Load terminals are in "Manual" mode, switched On and Off manually. It was On. Other modes are Automatic aka sun sensor - switching On when sun comes up, and Automatic+Timer.

Load terminals didn't disconnect, fridge was cycling until the battery dropped to 11V - it was supposed to do LVD 12.6V AND give low-voltage warning at 12.7V. The app says "Alarm", the manual - "Warning", so could've been just a blinking light, no alarm. Lost in translation from Mandarin.

I think the fridge disconnected at 11V, not the Load terminals. Other users complained that this fridge does LVD at 11 no matter whether you set it to 9 or 12.

Battery BMS has 10V LVD, so it didn't come to this.

StirCrazy - yes, I got the Bluetooth dongle and app. Paid CAD 20 or so on Aliexpress, Renogy wanted CAD 49. Without dongle you can only switch between pre-program settings for AGM, FLA, Li and User-defined. All modes have Discharge Limit 10.6V and LVD 11V. Maybe somebody could explain what Discharge Limit is and how it can discharge to 10.6 after Load was disconnected at 11.

In User mode you can change these values. In the app there is no LVD (!) but there is Discharge Limit and Over Discharge - the latter must be LVD. It is possible that I set LVD below 12 - called misleadingly "Over Discharge" in the app, and what happened to mysterious Discharge Limit set to 12.6 I don't know, since LVD aka Over Discharge had kicked in at 11. They could've used same terminology in the Manual and the app. After I'm done with the fridge, I'll experiment more with Discharge Limit and Over Discharge.

[3_tons]

pianotuna wrote:
3 tons,

I've seen some documentation that suggests a full charge once every 30 days.

But I don't see how this could destroy Almot's charge controller. Or have I got the wrong device?

PT, I didn’t mean to suggest that this had any adverse effect on his charge controller…
As far as the 30 days goes, I believe that there are several variables to consider including the number of up and down (but less than a full 100% re-sync) charge cycles, each of which over a time can contribute to a cumulative meter drift - JMO

3 tons

[ajriding]

Im not sure what the question is exactly.

What the fridge uses to determine SOC is unknown. Is it when the fridge is running and erroneously showing a lower voltage, or when it is not running and can sense the real voltage from a still battery?

When my fridge runs the voltage will show 0.6 to 1 volt lower charge than what it actually is, this is bc the fridge is using voltage right then. As soon as it shuts off voltage goes back up (or at least the voltage shown on the fridge display).

I am guessing that the low voltage shut-off function is actually a low voltage do-not-start function, so when voltage is below your preset cut-off then the fridge will not start. As opposed to - the fridge shuts off in the middle of a cycle when voltage is low.

I would connect fridge directly to the battery and not the solar controller/ load terminals (if this is what you are talking about). You will get the best power straight from battery. You may be seeing issues with the controller not knowing exactly what the batt voltage is. Are you on solar with 18 volts of solar coming in? The charge controller should see the battery voltage, but with a full charge voltage running down the same line it might get confusing for the controller. The controller might stop charging for a milisecond to read the battery, but IDK.

Your fridge will not use enough amps in a day to run a good battery (pair) down, so as long as you charge back every day and are not using huge amps for other devices at night you should not have to use a cut-off option. Mine just never draws the batts down that much over night and my fridge is double yours.

I too put massive insulation around my fridge. Not those near useless blanket velcro things they sell for hundreds, but real styrofoam held tight to the fridge. I put foam on the base and the sides, but just use a towel on the top for ease of use (chest-style top open).
The fridge runs way way less than it used to as the insulation really works, and a big bonus is that the fridge is super quiet now. I can't hear the compressor if I have a small slow fan running at night. if I listen really close I can tell when comp comes on but it is so faint now compared to before.

I think the biggest thing you can do is use insulation. Mine is 2 inches thick, it is the packing styrofoam that the fridge came with around it. No air gaps, no pockets, keep it tight fitting.
No matter how much or how little amps it pulls, when it is insulated and runs less the total amps used is less and this saves the battery.

[pianotuna]

3 tons,

I've seen some documentation that suggests a full charge once every 30 days.

But I don't see how this could destroy Almot's charge controller. Or have I got the wrong device?

[3_tons]

As per my previous, while it may be in the best interest of LFP longevity to routinely cycle the battery’s charge envelope to somewhere between say 10-90% SOC (thereby deferring a periodic full 100% SOC recharge - though, cell re-balancing as well), but the potential for ‘cumulated’ meter drift needs to be considered, as well as the possibility of ongoing cell-imbalance…Conversely, a constant ON charge (whether a ‘constant on’ dc-to-dc charger or solar…) strategy might well alleviate cumulative drift, but likely at the sacrifice of a few charging cycles…However, depending on camping style (and one’s age - lol!), this small reduction in battery life (a relatively very long span) may never be appreciably realized, thus a fair enough proposition…A good compromise might simply be to allow a periodic recharge to a full 100% SOC…Just saying…

3 tons

[pianotuna]

The load terminals on my Blue Sky are used as a "sun sensor" switch. Perhaps yours are too?

[3_tons]

While LFP’s don’t routinely need to be charged to a full 100% SOC, overtime (following multiple up and down cycling events - avoiding a meter re-sync…), you might unknowingly be experiencing the effects of a cumulative meter drift, along with an associated low voltage, or even a BMS cut-out… Meter drift can happen with FWC’s as well, but more likely with LFP where the practice is to avoid or seldom preform a full 100% SOC re-sync…In this case (due to cumulative meter drift scenario…) it is possible to have arrived at a lower than realized voltage or SOC while floating on solar…

3 tons

[StirCrazy]

Almot wrote:
Toying with a new to me 12V compressor car fridge. Cheap Chinese box, LG compressor, 50L volume split ~28L fridge, 22L freezer. The goal was to see whether my added insulation made any difference: Reflectix taped around the box, and an ugly cover made of an old bed spread - it had some "fur" inside.

Fridge draws >34AH per 24 hrs at 75F ambient, though in defence of a cheap box I should say that the freezer bin is huge and set to -2F. Fridge set to 39F.

Fridge connects to Load terminals of Renogy,
Renogy connects to 12.8V 120AH LFP,
LFP connects to nothing, partially charged.

Busy with other things, I suddenly noticed that don't hear quiet "purr" of the fridge. MPPT is blinking "battery problem", voltage 11.

Renogy Load terminals were supposed to cut the load off at 12.6V, - they didn't.
Renogy Low-voltage alarm was supposed to sound at 12.7V, - it didn't.

Independently, darn ice box didn't cut off at 12V either - downstream from MPPT on a thin #18 cable it reads lower voltage, so LVD 12 is a-okay, only it didn't cut off.

Yeah, I know, buy Victron, I've been warned. Still curious whether I did something wrong, other than buying Renogy.

did you ever get the bluetooth dongle and get the app? I only have the porch light on my load and it works great but the only settings I saw were time based.. ill take another look at mine as the only issue I have had was with a bottle of scotch bumping into my quick disconect breaker for my battery bank. :R

[Almot]

Don, the fridge is drawing 2.5-4.5A when cycling. Renogy load terminals are rated 20A.

[pianotuna]

Load terminals are often used to control a relay. Large loads may cause failure.

So my guess it was this item that caused the grief.

If it is any consolation--a Victron might well have failed, too.