Battery temperature

[SternWake]

I've been collecting some temperature data from various charging related objects, such as my Alternator, External Voltage regulator, battery, and plug in power supply/ charging source.  

I either am using Arctic silver thermal epoxy or thermal grease and Gaffers tape to adhere the sensor tip to the item being measured.

What I have found surprising is the battery temperature rise during high amp charging such as from my 40 amp power supply or alternator.  My battery this morning went from just under 70F to over 90F in an hour and a half.  It was taking 35+ amps for about 45 minutes before amps started tapering at absorption voltage.

Higher battery temperatures  over 77F will actually increase the total available capacity of the battery.  Being a large thermal  mass this heat from charging can be maintained for quite some time during discharge, and discharging the battery also creates some heat helping to maintain high than ambient temperatures of the battery and apparently a higher capacity too.

Basically the increased battery temperature can help make the battery appear to be more fully charged and healthier than it actually is.  Combine this with the surface charge that remains after a charging source is removed, can really fool the person with only a Voltmeter into thinking their battery is more charged and more healthy than it actually is.  Battery temperature is also why when a super cold less than healthy battery can't start a super cold engine.

I am also surprised how much heat the battery maintains overnight, often staying 10 to 15 degrees hotter than ambient temps, and my battery is under the vehicle, not inside it.

My temperature data has me lowering absorption voltages somewhat.  That said, this particular battery (Northstar group27) has been charged at higher than ideal voltages in its life upto now and is performing very well still with 350+ deep cycles on it and many hundred more shallow cycles on it, and a few thousand engine starts as it is currently my Only battery for both house and engine starting duty.

Its location under  the van's floor behind driver's seat indicates it is also bathed in engine heat when driving and getting hotter than expected just from that, not only from high amp charging.

Even now, unmoving, accepting only 6.2 amps at 14.3v, battery temperature is holding 93F, Gonna lower voltage to 14.2 or so.

I used to assume battery temp was within 5 degrees of ambient.  My assumption was very very wrong, but thankfully There appears to be little damage from too much charge voltage for the temperature, and perhaps it has helped prevent sulfation as Mainsail has data showing slightly higher absorption voltages over manufacturer recommendations appears to stave off sulfation on regularly deep cycled batteries, but I probably have caused it to offgass somewhat and it might be healthier otherwise.

Actual Data has been very enlightening, but there is certainly bliss in ignorance and ignorance in bliss.

I've been using this 4 channel temperature gauge for monitoring various sources.  K type thermocouples ore the type digital multimeter use, and are pretty cheap.

I will be adding more sensors to various things like my radiator inlet and outlet and thermostat housing, perhaps transmission cooler lines too.

https://www.amazon.com/Perfect-Prim...ie=UTF8&qid=1466792658&sr=8-7&keywords=K+type

 

[AngryVanMan]

Good observations!  Lower absorption and float voltages at higher temperatures are definitely recommended, although undercharging seems to be the more common problem on a lot of RV systems due to voltage drops that are not accounted for in the wiring, at least according to HandyBob's solar site.  Most of the solar charge controllers I've seen include an automatic temperature compensation feature for lead acid batteries.  The charging inefficiency of lead acid batteries must create a lot of heat, which I guess makes sense - around 10% charge energy converted to heat at half full, and as much as 40% converted to wasted heat as you get closer to 100% charge.

There's a difference of almost 2 full volts between 30 degrees and 120 degrees (F) recommended charge voltages! [random battery charging pdf file]

 

[SternWake]

Yes, and my Northstar AGM is a very low resistance AGM battery, meaning it should heat much less than a flooded/wet battery in the same charge regimen, Yet the temperature increase is rapid and much more than expected.


My Charge controller, blue sky SB2512i, does not adjust voltages for temperature.  I should have spent the extra 35$ at the time for the sb2512iX model which does allow for a battery temp sensor to be utilized.

Alternator temperature has been enlightening too.  Idling parked at full output and the temp increases as if someone took a propane torch to the casing.  Moving it drops to a nice 110F at near full output in my Van.

Even driving slow and lower rpms cause alternator temp to rise dramatically quickly when loaded with depleted battery or other loads.

 

[blars]

Good alternators will drop the charge current as they heat up -- trying to charge a LiFePO4 (or large bank of lead-acid) from an alternator that does not have this feature can burn it up.

 

[jimindenver]

On a warm day it doesn't take the Lifelines long to heat up if we have taken them down a few hundred Ahs. It takes putting the system on them in full light so that they will suck up the full 50a for a while. When they are lightly cycled and the solar brings them up slowly from dawn, the temperature doesn't change much even though we see from below freezing to 70 or 80 above daily up there. Luckily we use so little over night that we barely burn off the overcharge before the sun comes up.

It doesn't take much to vent for gasses according to our mutual friend. Talking to a battery shop about installing three 8-D's and they wanted two vents, one high and one low for heat removal to get the warranty. With the heat they can put off I'd have to agree. they get hot, the controller gets hot, the inverter gets warm and so does the converter/ charger. That's a lot of heat in the cabin during hot summer days.

That does bring up a interesting thought that I will have to see if the charts I have show it. The TC should be adapting to the battery temps and around 100* it doesn't agree with Lifeline.

 

[SternWake]

Alternators themselves can only regulate current if the voltage regulator is internal to them. Otherwise they will seek the voltage the regulator demands and can burn themselves up if the batteries are low resistance and hungry. Semantics, but voltage regulates current.

The depth of discharge definitely plays a huge part as when batteries are below 80% charged they can basically take a lot of current and from 80% charged, ~ 3.5 hours or more at absorption voltage, for nearly the whole 3.5 to 4 hours, the battery is still heating even at a relatively low amperage.



I've been very surprised that the battery still heats up to the point it can accept about 2% of its Ah capacity, then levels off, then will try and decline as it approaches 0.5% of capacity.

Interested in observations in winter, well what passes for winter in San Diego. Right now I have 4 sensors, one on the Meanwell, one on the battery and two basically just hanging out in free air inside the van.

The battery is the hottest one at 71.2, the others read 68f. 1:30 Am, only 14Ah from full. I am guessing if I were 30Ah or more from full at this point, the battery would be 75f or more, but I was in a stick and brick rewatching 'Breaking Bad' from the beginning with someone who has not seen it and was not sure they wanted to. They no longer think that.

 

[SternWake]

Kind of a heads up in the battery temperature data thread.

San Diego coastal has been getting into the mid 80's, and my battery, cycling to nearly 50% each night, is rarely dropping below 82F even by sunrise. It is staying warmer during overnight discharge( ambient temps fall to ~65f), and warming up a lot more than expected during charging, and especially high amp recharging.

I've been lowering charge voltages significantly at these elevated battery temperatures, but kind of freaked out when I saw battery temperature at 98f and expected it to be more inline with ambient temps some 15 degrees lower.

I saw 98F at 14.4v accepting 7 amps and lowered voltage to 14.0 and it only took 4.5 amps to hold 14, but temperature still kept climbing.

I think The High amp alternator/ plug in recharging a depleted battery over thick cabling in hot ambient temperatures is likely more abusive to lifespan than this same battery not getting fully charged that particular cycle during hot weather.

In the past I've said how important 100% charged ASAP as often as possible is to ultimate longevity, but my battery temperature data reveals that in a heatwave one must be more aware of how much hotter the battery actually gets, and temperatures above 120F, the electrolyte basically starts chewing up the lead plates, so steps should be taken to prevent battery temperatures reaching these levels regularly.

120F electrolyte with regular absorption voltages applied via a high amp charging source to a depleted battery 'could' be 'very ' detrimental the battery.

We can compare all the batteries scorching in Arizona's summer heat when underhood in vehicles, but we have to remember that starting batteries underhood in daily drivers rarely work hard at all, and are rarely discharged much at all, and as such cannot accept high amperages and will not heat up nearly as much from charging. Combine these hot ambient temperatures with a depleted battery receiving high amperage at or nearly at absorption voltages, and the temperature the battery reaches could be in the danger zone and no doubt erode the lead plates and battery capacity faster.

As Van dwellers, we ask more of our batteries than the regular vehicle driver. Hot temperatures with high charging amps into our depleted batteries, is more likely to have out batteries approaching and exceeding 120F.

The battery temp sensor on my low resistance AGM battery, has been very enlightening. I might do some modifications which might allow less engine heat near my under van body battery at speed, as that is a huge factor as well, and not one which really played much part in these recent heatwave battery temp data observations.

Seems 120F battery temperature could be all too easy to attain in high ambient temperatures, and ALL battery manufacturers recommend letting the battery get no hotter than this.


If you are baking in this heatwave, and using your batteries hard, consider taking their temperature on either side of noon when charging. Lowering absorption voltage to artificially limit charging current, if possible with your setup, could help the battery live longer.

Really wish my solr controller had the BTS option. i have to push a series of buttons about 2 dozen times to limit voltage. So much easier to twist a potentiometer watching a voltmeter.

 

[jimindenver]

With the temperatures we have seen in Denver, the TS-MPPT-60's temperature compensation doesn't agree with Lifelines guide lines, so I put the panel on the Eco-worthy 20a MPPT controller instead. It takes seconds to manually set the voltage set points to agree with Lifeline, I have to hook a computer up to the big controller.

 

[blars]

the TS-MPPT-60's temperature compensation doesn't agree with Lifelines guide lines,

The TS-MPPT-60 is programmable, you can set the voltages, temperature compenstation, etc. to whatever you want. Temp comp is et to 0 on mine for my LiFePO4 bank.

 

[jimindenver]

It's been a while since I had a computer on the controller but I didn't see a way to change the compensation for when it was over 90F or under a certain degree. So I would have to get and change the settings when it got too hot and back again when the heat wave broke. It's far easier to change the settings in the smaller controller while the bank sets and waits for the docs to say I can lift the stinger to the trailer again.