Does it make a difference where I connect a Remote Temperature Sensor

rcteel5 · April 2018

I am new at this. I have a cabin in a very remote area in Michigan that can get in the 90's in the summer, and 20+ below zero in the winter, so I want to add a battery temp sensor to assist in charging.

I have a 12 panel (4KW) system with a MagnaSine MS4448PAE Inverter and an Outback FlexMax 80 charge controller. Both of the devices have an optional Remote Temp Sensor available. Does it matter which device I connect a sensor to? (I haven't bought the sensor yet). I would appreciate any advice you can give!

littleharbor2 · April 2018

Typically you place them about 2/3rds of the way up the side of the battery case. In a bank of batteries place it on an inner battery, not out on the perimeter. Some sensors are designed to bolt onto a terminal, I'd say still on an inner terminal.

BB. · April 2018

You can also get a block of styrofoam, carve a recess in it, and glue or strap or wedge over the remote sensor on the side of the battery (want battery temperature, not air temperature).

Bill

Vic · April 2018

And, the FM 80 definitely needs the BTS, if you use the Inverter to do much charging, it should also have one.

As littleharbor mentioned, place both sensors on the same battery in center of the pack, an inside surface of the battery.

If the only charging that you do with the inverter is, to Bulk just to the Absorb voltage, then you could probably get by without a sensor on the inverter (but, in an emergency, you may need to Abosrb and even EQ from the inverter, so why not bet both?). IMO, Vic

Estragon · April 2018

If the ambient temp changes quickly (eg. in a shed that warms quickly when the sun hits it), you might also want to add a bit of insulation covering the sensor. The banks thermal mass changes temp slowly, and the sensor can be less accurate if exposed to more rapidly changing ambient temps.

Ideally, the bank would be in a location with fairly stable temps. Extreme heat shortens lifespan. Cold reduces apparent capacity, and has a risk of damage from freezing at low states of charge. I have a similar climate (a bit colder in winter), but in an insulated but unheated crawlspace the bank doesn't get much colder than ~15°f or warmer than ~65°f.

rcteel5 · April 2018

Wow, this forum is great. Thanks to all of you!!! Can't believe how quickly I got an answer.

So just to clarify, it sounds like I should have 2 sensors. Most of the time my charging will come via the solar panels (Flexmax 80), but there will be times (especially in the winter) when the charging may come from the inverter/generator so I would benefit from the MagnaSine with sensor. Is that correct?

Vic · April 2018

Hi rcteel5,

If you will use the MagnaSine to do Absorbs and perhaps EQs, then having the inverter able to adjust the charge voltage, based upon the actual, measured battery temperature.

So if that is the case, then, YES, for the cost of the sensor, it should be worth it.

The Bulk charge stage is not a voltage-regulated stage, so the battery temperature is not used, in general.

Vic

BB. · April 2018

However, if you do many hours of Equalization charging, the batteries can overheat very easily.

EQ charging is generally around 2.5 to 5% charging current (bank 20 hour capacity rating).

Bill

rcteel5 · April 2018

I mentioned in my first post that this is all new for me. Could someone help explain what conditions cause charging to originate from the MagnaSine inverter versus the FlexMax charge controller? I am completely off-grid. Input sources are either the solar panels or 12KW backup generator with auto-start. With only a year under my belt with this system, I have noticed the generator rarely runs for 7-8 months (mainly just monthly maintenance runs), but it runs weekly during the winter. Thanks again for your help and patience.

mcgivor · April 2018

There would be settings programed into the auto generator start "AGS" system which would enable the generator when the battery voltage drops below a set threshold for a given amount of time, the termination of the generator run would be typically when the absorption charge stage is complete. There can be other parameters programed depending on the AGS, current, state of charge etcetera.

Estragon · April 2018

I find that the low winter sun plus short days means solar isn't enough to fully charge batteries every day. From early Dec to early Jan, the sun barely makes it above treetops.

Running the generator alone to fully charge batteries is a bit of a waste of fuel IMHO though, and can be hard on the generator. Current required for charging drops off steadily after absorb voltage is reached, so the generator gets only lightly loaded. To make the process more efficient, I start the generator manually in the morning so the transition from bulk to absorb is around when whatever sun there is starts hitting the panels. When charging current is dropping off in absorb, I stop the generator and let pv finish charging.

I would definitely use remote temp sensors on all charging devices. They're pretty inexpensive, and even though my inverter RTS isn't really used , I have it connected and the inverter set up to compensate anyway.

Does it make a difference where I connect a Remote Temperature Sensor

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