High Temperature Issues?

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marcustcohn

Member
Joined
Jun 27, 2011
Messages
6
How hot is too hot?

In La Quinta CA the daytime highs have been 115 or more - nights are a cool 90. My garage has to be 125 at its high point but cools off to about 100 overnight. Page EV-21 of the owners manual suggests not exposing the battery to over 120 for 24 hours in a row - is this because battery charging is exothermic and a battery that is hot to start with should not be charged? How hot does a battery get during charging at normal temperatures? To quote Jerry Reed - 'When you're hot you're hot!!!'
 
marcustcohn said:
How hot is too hot?

In La Quinta CA the daytime highs have been 115 or more - nights are a cool 90. My garage has to be 125 at its high point but cools off to about 100 overnight...
If your garage is really running 10° hotter than outside, I'd install some ventilation. Not just for the LEAF, either.
 
Venting a garage is problematic - the windows in this one are on the alarm system. I have checked a few garages and most run somewhat hotter than the outside temperature depending on how much direct sun hits the garage door and how well insulated the door is. Actually, this garage gets relatively little direct sun - it's just that the radiated infra red collects. By the by, most garages here in the desert are just as hot.
 
marcustcohn said:
Venting a garage is problematic - the windows in this one are on the alarm system. I have checked a few garages and most run somewhat hotter than the outside temperature depending on how much direct sun hits the garage door and how well insulated the door is. Actually, this garage gets relatively little direct sun - it's just that the radiated infra red collects. By the by, most garages here in the desert are just as hot.

The worst mine has gotten so far is 110 with an outside temp of 118. Today may be a good test because it is supposed to hit 116 at Sky Harbor which means it will be in the 120's here (already 118 at 2 PM). Right now the garage is 106. The only exposure is the east and west sides. The door gets very little sun since it faces North.
 
Lithium-ion batteries are very efficient at slow charge rates, within a reasonable SOC like 80%.. usually around 99% efficient. When the battery reaches the ends of the SOC is when it starts to heat up.. I am sure the BMS will automatically stop the charging process if it gets too hot.

The issue is the accelerated aging at elevated temperatures, and 120° F is elevated... at 130° F I would start running :)

I'm not sure if the charging process is exothermic with lithium-ion, it is with nimh and endothermic with nicad.. yes nicads get colder as they charge.
 
marcustcohn said:
Venting a garage is problematic - the windows in this one are on the alarm system.
I was thinking a roof vent or one high on a wall, plus one low in a wall or door. Just seems like a large temperature differential to have all the time. Are the windows in full sun? Maybe some tinting would help.
 
garygid said:
Or, alum-foil, shiny side out, on the inside of the windows will reflect a LOT of heat.

If the OP has an HOA, they may not allow aluminum foil (ours doesn't allow it). They may not let you tint your windows either unless you get it approved with the architectual committee.
 
The old rule of batteries is that lifetime is halved for every 10 degrees C (18 F) of average lifetime temperature. Charges and discharges (driving) have a much larger impact that just sitting in the sun or in the garage at high temperature. That's why electric vehicles don't like heat. One word of caution, this is a general rule that works more or less for most types of batteries. Li-ion guys seem to believe it too, but I haven't seen papers that experimentally confirm or disprove that it's really half. Certainly there is an impact and, for instance, accelerated aging tests are performed at high temperature.
 
If you have to operate an ICE car and park it inside the garage, the heat from the engine can easily raise the ambient temperature up quickly and be trapped in an enclosed garage for a long time, too. I cut a vent hole in my garage ceiling and opened my garage door just a crack at the bottom to create a convection flow and let the hot air escape into the garage attic.
 
Volusiano said:
If you have to operate an ICE car and park it inside the garage, the heat from the engine can easily raise the ambient temperature up quickly and be trapped in an enclosed garage for a long time, too. I cut a vent hole in my garage ceiling and opened my garage door just a crack at the bottom to create a convection flow and let the hot air escape into the garage attic.
I certainly hope that attic is well ventilated. Overheated attics are a source of many problems, not the least of which is fire. Perhaps you could continue your garage venting through the attic directly to the roof.

Glenn
 
Glenn said:
Volusiano said:
If you have to operate an ICE car and park it inside the garage, the heat from the engine can easily raise the ambient temperature up quickly and be trapped in an enclosed garage for a long time, too. I cut a vent hole in my garage ceiling and opened my garage door just a crack at the bottom to create a convection flow and let the hot air escape into the garage attic.
I certainly hope that attic is well ventilated. Overheated attics are a source of many problems, not the least of which is fire. Perhaps you could continue your garage venting through the attic directly to the roof.

Glenn
Good point. My attic above the garage has its own vent, and is connected to and wide open to the roof so there's definitely no problem with the air flow from the garage attic to the roof out to the roof's vent as well as out to its own vent.

Wouldn't it be a design flaw for any attic space not to have a vent out to somewhere?
 
Volusiano said:
Wouldn't it be a design flaw for any attic space not to have a vent out to somewhere?
Indeed it would be, but trust me, there are plenty of real world scenarios that have just such a "flaw!"

Glenn
 
We have too many crickets to allow the garage door to stay open, even a crack, but if you don't have those and other creatures (scorpions, black widows, etc.) then it sounds like a great idea. But since we need a new hot water heater anyway, we're going to buy a heat pump hot water heater (GE GeoSpring) that takes the heat out of the garage and will heat our hot water using only 550W instead of 4500W. It will be interesting to see how many degrees it will lower the garage's temp.
 
Glenn said:
Volusiano said:
Wouldn't it be a design flaw for any attic space not to have a vent out to somewhere?
Indeed it would be, but trust me, there are plenty of real world scenarios that have just such a "flaw!"

Glenn

Actually some of the more energy efficient houses being built today don't have vents in the attic. They spray isocyanurate insulation on the underside of the roof deck and the attic space becomes "conditioned space." The result is an airtight (or closer to air tight) attic and cooler temps for the AC ducts.

If you had this kind of arrangement in your attic you would probably know about it. And since Volusiano said he already has a vent from the attic to the sky, then he probably doesn't have this setup either.
 
Well - an apology to all. Actual data tells a different story. The garage oscillates between lows that are higher than the ambient lows and highs that are LOWER than the ambient highs. I am having more (some?) insulation added to the attic over the garage and considering a ventilation fan that will operate during the late evening hours to give the garage a 'running start' in the morning. So no 125 degrees - the actual measured high was 103 vs. ambient 110.
 
marcustcohn said:
Well - an apology to all. Actual data tells a different story. The garage oscillates between lows that are higher than the ambient lows and highs that are LOWER than the ambient highs. I am having more (some?) insulation added to the attic over the garage and considering a ventilation fan that will operate during the late evening hours to give the garage a 'running start' in the morning. So no 125 degrees - the actual measured high was 103 vs. ambient 110.
Just goes to show that heaps of guessing can't hold a candle to actual measurement.
 
LEAFfan said:
Herm said:
You could also screen the air intake so that critters dont get in.

I was talking about the small garage door opening...that can't be screened.

You can make a hole anywhere and then screen it. On a door would be easiest.. screen it with steel mesh on one side for security and insect screen on the other for insects.
 
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