Temp sensor placement with two battery locations?

vsheetz · July 2013

Morningstar TriStar TS-60 PWM - six 100w PV panels.

Two pairs of Trogan 105 6 volt batteries - the two pairs wired in parallel. One pair (A) located on one side of motor-home under the entry steps, the other pair (B) on the other side of motor home in a storage compartment. About 15' of cable connecting the two pairs. Pair A is where the motor-home loads and TriStar voltage sense are connected. Pair B is where a DC2AC inverter and the TriStar charge wires are connected.

Should I be using a temp sensor and if so where should it be located - at pair A or B? Or does it even matter where located?

Thanks in advance!

BB. · July 2013

Re: Temp sensor placement with two battery locations?

The hottest battery will be most sensitive to over charging (Lead Acid batteries require a reduction in charging voltage of ~ -5 mVolts per degree C per cell below ~25C).

So, which ever battery bank runs the hottest would be the place to put the temperature sensor...

However, this sounds like a difficult setup to make run "right".

Batteries should be together to be at the same temperature (ideally, you want the batteries to run between ~50 to 80F)... Too hot, and they can age faster. To cold (below freezing) and they will lose "apparent capacity".

Batteries should be wired so that each parallel string is "matched" with same wire size/lengths. Otherwise, the battery string with the lowest resistance will carry most of the charging/discharging current.

Also, you want a short/heavy set of cables from the charge controller to the battery bank. And short heavy cables from the batteries to the AC inverter/loads.

I would highly suggest that you rebuild the battery bank/box so that you can have all of them in the same location--and that the Charge Controller+AC inverter are also close to the box/bank.

If you give us the size of solar array + AC inverter (maximum loads you wish to support), we can help you with wire gauge/lengths.

-Bill

vsheetz · July 2013

Re: Temp sensor placement with two battery locations?

I would not think the ambient temperature of the two battery areas would differ appreciably, so sounds like it matters not a whole lot.

Getting the two pairs of batteries is not going to happen as neither area has additional space.
Short heavy cables are in already in place from the B pair to the inverter and charge controller.

While not a optimal setup it has provided good service for over 10 years, and this with the original batteries until just recently.
Albeit the PV system is new to the mix.

Thanks!

vtmaps · July 2013

Re: Temp sensor placement with two battery locations?

vsheetz wrote: »

I would not think the ambient temperature of the two battery areas would differ appreciably, so sounds like it matters not a whole lot.

Its not so much about ambient temperature. Batteries make heat while charging and discharging. Because of the way your batteries are connected they will not share equally in the charging and discharging. Therefore one set of batteries will be warmer.

btw, even if you have perfect wiring (and you don't) parallel batteries are unstable with respect to heat generation... if one battery draws more current than the other (inevitable) it will run warmer which makes it draw more current which makes it warmer which makes it draw more current which makes it warmer.... thermal runaway!

Buy yourself a cheap DC clamp ammeter and measure the current in each battery pair while charging... you will see how unequal they are.

--vtMaps

Desert Rat · July 2013

Re: Temp sensor placement with two battery locations?

I agree with Bill; the sensor should go to the hotter of the two pairs of batteries.
It's not an ideal setup as others have said, but sometimes ya gotta do what ya gotta do. I hope the cable connecting the batteries is no smaller than 4/0!
You might consider swapping locations of the batteries every couple of months to help equalize things.

BB. · July 2013

Re: Temp sensor placement with two battery locations?

A lot of our concerns are based on assuming you have a "larger" AC inverter (and/or DC)... If the Inverter is smaller and/or your peak/average power needs are lower (i.e., C/20 vs C/8 or C/5 levels of discharge current--400 AH @ 12 volt battery bank discharging at 20 DC amps vs 50-80 amps) will reduce the concerns over excessive cabling lengths and battery balancing issues).

If the system has been meeting your needs and you have been getting >5-7 year battery life--Hard to argue with success.

-Bill

vsheetz · July 2013

Re: Temp sensor placement with two battery locations?

The inverter is sized large to enable the microwave to be used without starting the generator. Usually a couple three minutes of this usage a couple three times a day. More typically it's powering the TV, a computer, etc. during the evenings.

OK, so I am a bit confused on exactly where the temp sensor is to be physically placed. Other. smaller, Morningstar controllers have a internal temp sensor and can optionally use a external sensor. So my understanding was the temp sensor was simply placed in the battery compartment, not attached to a battery. Is it actually attached to a battery terminal or what? The Morningstar instructions do not state specifically.

Thanks for the help!

From the TriStar manual:

Remote Temperature Sensor (RTS)
If the temperature of the system battery varies more than 5˚C (9˚F) during the
year, temperature compensated charging should be considered. Because the
battery’s chemical reactions change with temperature, it can be important to
adjust charging to account for the temperature effects. The RTS will measure
the battery temperature, and the TriStar uses this input to adjust the charging
as required.
The battery charging will be corrected for temperature as follows:
• 12 V battery – 0.030 Volts per ˚C (–0.017V per ˚F)
• 24 V battery – 0.060 Volts per ˚C (–0.033V per ˚F)
• 48 V battery – 0.120 Volts per ˚C (–0.067V per ˚F)
The RTS should be used only for battery charging and diversion control. Do
not use the RTS for load control. The charging parameters that are adjusted
for temperature include:
• PWM regulation
•*Equalization
• Float
• High Voltage Disconnect
See Installation, Step 4, for connecting the RTS to the TriStar

unicornio · July 2013

Re: Temp sensor placement with two battery locations?

I think there is no solution to compensate the temperature, with a single charger, of two batteries that located in different places... put the sensor in the warmer battery is more successful for security, but this does not make that the colder battery is charging properly ...in addition, the temperature effect exacerbates the problem even more when the two batteries are connected in parallel, and is aggravated even more still, if parallel wiring of the batteries is not compensated ...

i want not to talk about charge controllers, which aim to compensate the battery temperature with a sensor that is located inside the controller box ... this best left aside and not touch it ...

BB. · July 2013

Re: Temp sensor placement with two battery locations?

Usually, the senor is bolted to a battery terminal or you can hollow out a notch on the side of a block of Styrofoam and put the sensor in the notch up against the battery (you really want the temperature of the battery internals, not the air around the battery).

The MonrningStar 15 Amp MPPT charge controller really needs the remote battery temperature sensor--I guess the controller is so small, the "ambient temperature sensor" gets heated by the local electronics and dials back the battery charging voltage too much (if the external sensor is not used).

Yes, you can put the charge controller in the battery enclosure--But you do run the risk of electrolyte mist (bubbling batteries during finish charging/equalization if flooded cell, or a venting AGM/GEL battery--Venting is bad for those batteries) corroding the expensive charge controller.

So--If you have the batteries in small boxes, I would avoid placing any electronics inside the boxes to keep the controllers clean and dry. And use a remote temperature sensor (especially if the controller ambient temperature is much different than the battery bank temperatures).

You want the controller to crank back on charging voltages to keep batteries from over charging. And if they run cold, higher charging voltage will more quickly and efficiently recharge the battery bank (very helpful for freezing climates).

If this is a 12 volt battery bank--A 1,500 watt inverter will draw around:

1,500 watts * 1/0.85 inverter eff * 1/10.5 minimum inverter voltage = 168 amps...

No small amount of current. The computer and TV (if energy efficient) will draw 1/10th amount of current.

-Bill

vsheetz · July 2013

Re: Temp sensor placement with two battery locations?

Further review of the Morningstar documentation I see where the temp sensor reading can be displayed, so I can move the sensor around and see what the temp delta is battery to battery and see which is highest temperature. The Morningstar sensor is housed in a battery terminal lug, so evidently is to be attached to a battery post.

Thanks all!

YehoshuaAgapao · August 2013

Re: Temp sensor placement with two battery locations?

With Xantrex, if multiple sensors are installed, it uses the warmest rating. This would favor finding the warmer pair and putting the sensor on those - safer. Hopefully they are not too different in temperature.

scrubjaysnest · November 2014

Re: Temp sensor placement with two battery locations?

This thread may be a little dated but I think still applies to us with RV's. The one thing that comes to mind with vsheetz's set up is how may panels does he have and would it be worth while to add a second controller therefore having one for each bank. This is a budget issue of course, but it would address the distance between banks and get temp comp for both banks.

Temp sensor placement with two battery locations?

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