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Open Roads Forum  >  Tech Issues

 > More fun with Renogy MPPT and LFP

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Almot

out there

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Posted: 10/28/21 10:21pm Link  |  Quote  |  Print  |  Notify Moderator

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.

pianotuna

Regina, SK, Canada

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Posted: 10/28/21 11:13pm Link  |  Quote  |  Print  |  Notify Moderator

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.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, soon to have SiO2 batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

Almot

out there

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Posted: 10/29/21 12:36am Link  |  Quote  |  Print  |  Notify Moderator

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

StirCrazy

Kamloops, BC, Canada

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Posted: 10/29/21 08:06am Link  |  Quote  |  Print  |  Notify Moderator

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. [emoticon]


2014 F350 6.7 Platinum
2016 Cougar 330RBK

3 tons

NV.

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Posted: 10/29/21 08:25am Link  |  Quote  |  Print  |  Notify Moderator

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

pianotuna

Regina, SK, Canada

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Posted: 10/29/21 08:57am Link  |  Quote  |  Print  |  Notify Moderator

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

3 tons

NV.

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Posted: 10/29/21 11:52am Link  |  Quote  |  Print  |  Notify Moderator

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

Regina, SK, Canada

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Posted: 10/29/21 01:20pm Link  |  Quote  |  Print  |  Notify Moderator

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?

ajriding

st clair

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Posted: 10/29/21 01:49pm Link  |  Quote  |  Print  |  Notify Moderator

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.

3 tons

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Posted: 10/29/21 02:32pm Link  |  Quote  |  Print  |  Notify Moderator

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

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