Battery Heat Barrier

Submitted: Monday, Jan 09, 2012 at 16:21
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After the recent upgrade to the Troopy's auxiliary battery system and the purchase of a replacement AGM battery, I turned my attention to the heat that the batteries are exposed to in the engine bay.

Now I know that it gets damned hot in there and I know that batteries, particularly AGM's, do not like high temperatures so I contrived to install a thermal barrier to protect the batteries. I used 12mm closed-cell foam with one-side foil backing. This was doubled-over to increase thickness and provide foil on each side then installed to segregate the engine bay. Being flexible it fitted rather well down to the inner mudguard and cooling air can flow through the grille but outside the radiator then over the batteries and exit down below the firewall.

Image Could Not Be Found

Now for the performance test:
It was only an extended local drive and lacked both the high ambient, high engine load and slow vehicle speeds of say the Simpson, but it was a preliminary test.

After a short run allowing temperature to rise from 30c ambient:
Engine bay 61c, Battery bay 45c
Engine bay 64c, Battery bay 46c
Engine bay 68c, Battery bay 48c and stabilised.

A significant reduction of battery environment temperature. I'm pleased at the improvement with little cost or effort. Perhaps now some fine tuning in the way of scooping more intake air.

Incidentally, I do not subscribe to the proprietary close-fitting battery heat protectors. Without the provision of internal cooling air flow they can only slow the transfer of heat and at the same time prevent the escape of heat caused by the charging of the battery.




Cheers
Allan

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Reply By: Bob Y. - Qld - Monday, Jan 09, 2012 at 17:06

Monday, Jan 09, 2012 at 17:06
Allan,

Very ingenious, and cheap. Fits the KISS principles to a "T".

You can buy flexible tubing, about 75mm, from Whitworths, that could be fitted from under the headlight, and bent up to near the front battery, that would give even greater cooling, Allan. But you may not need it, with the temps you've posted.

I've got some Aircell insulation, that would be perfect for that application too.

Bob.

Seen it all, Done it all.
Can't remember most of it.

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Follow Up By: Allan B (Member, SunCoast) - Monday, Jan 09, 2012 at 17:20

Monday, Jan 09, 2012 at 17:20
Thanks Bob, I actually have some 150mm flexible ducting that could be incorporated to maybe improve performance. I'll look at it.

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Allan

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Reply By: Olsen's 4WD Tours and Training - Monday, Jan 09, 2012 at 17:19

Monday, Jan 09, 2012 at 17:19
What holds it in place?
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Follow Up By: Allan B (Member, SunCoast) - Monday, Jan 09, 2012 at 17:50

Monday, Jan 09, 2012 at 17:50
Hi David,

Generally it fits snugly between the mudguard and air-conditioner pipes but at the rear it it glued and cable-tied to a 250mm length of 40x40 aluminium screwed to the firewall. I was looking for a good seal there. At the front it is simply a "force" fit behind the grille/headlight bodywork. With the bonnet closed it bears against similar insulation attached beneath the bonnet for another good seal. It's going nowhere! In three places at the bottom it was necessary to provide slits to pass a/c pipes and cable looms.
It does not interfere with normal vehicle maintenance but could easily be removed without damage if necessary.


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Allan

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Reply By: Atta Boy Luther - Monday, Jan 09, 2012 at 18:52

Monday, Jan 09, 2012 at 18:52
I just put some washers under the bonnet hinge bolts and made a gap where the bonnet sits near the windscreen . They used to do it in the seventies with v8s .
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Follow Up By: The Explorer - Monday, Jan 09, 2012 at 19:10

Monday, Jan 09, 2012 at 19:10
Yeah - seen it done on small Landcruiser mounted drill rigs as well (in the 80's and 90's and 00's:) Provides an escape route for the hot air when stationary ..suppose it works when you're going real slow as well.

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Greg
I sent one final shout after him to stick to the track, to which he replied “All right,” That was the last ever seen of Gibson - E Giles 23 April 1874

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Reply By: Rockape - Monday, Jan 09, 2012 at 19:09

Monday, Jan 09, 2012 at 19:09
Alan,
you certainly have dropped the temps, well done.

You could get the vent that was through the side of the mudguard on the earlier 2H 75 series cruiser and fit that. I have also seen the inner guard at the front opened up to let airflow up to the batteries. The air flows between the inner and outer guard and enters the battery bay through the existing holes. That seemed to work well.

Have a good on,
RA.
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Reply By: Eric Experience - Monday, Jan 09, 2012 at 20:46

Monday, Jan 09, 2012 at 20:46
Allan.
You are on the right track keeping the temp down, have you taken an of cut of the foam and put a match to it, you may end up pulling it out if it is the foam that I think it is. I used a sheet of light gauge aly dimpeled with a ball pane hammer and then folded like yours. Eric.
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Follow Up By: Allan B (Member, SunCoast) - Tuesday, Jan 10, 2012 at 00:12

Tuesday, Jan 10, 2012 at 00:12
Hi Eric,

Yes, it did occur to me to test the foam flammability and it will burn whilst the cigarette lighter is applied but self extinguishes when the lighter is removed. Just the same I am going to seek some other insulation which is totally fire-proof. Maybe even just an aluminium sheet would produce sufficient barrier if the cooling air flow is high enough. Or maybe two aluminium sheets with glass wool between them.

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Allan

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Reply By: Member - Phil G (SA) - Monday, Jan 09, 2012 at 22:07

Monday, Jan 09, 2012 at 22:07
Gday Allan,

Thanks for posting the temps - I run a similar shield along the inside of the double battery tray.

With reference to AGMs, Bill Darden's battery FAQ says "For every increase of 10°C above 25°C, the battery's life is cut in half due to positive grid corrosion or the self-discharge rate is doubled."

My AGM still lives in the canopy, and not under the bonnet!

Cheers
phil
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Follow Up By: Battery Value Pty Ltd - Monday, Jan 09, 2012 at 23:12

Monday, Jan 09, 2012 at 23:12
very true Phil,

this was a reference to the Arrhenius equation which pertains to all thermally induced reactions, not just AGM batteries.

Even flooded cell starting batteries would last a lot longer if they weren't mounted under the bonnet.

cheers, Peter
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Follow Up By: Allan B (Member, SunCoast) - Tuesday, Jan 10, 2012 at 00:04

Tuesday, Jan 10, 2012 at 00:04
Hi Phil,

I do have an AGM in the cabin, but there is no room for the second one there so when I replaced the flooded deep cycle in the engine bay with an AGM I was more or less forced to put it in the engine bay, hence the thermal insulation. But of course, time will tell. Experimentation all in the name of science!

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Allan

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Follow Up By: Member - Phil G (SA) - Tuesday, Jan 10, 2012 at 15:31

Tuesday, Jan 10, 2012 at 15:31
Gday Allan,
Science and numbers are good!
I used to have a thermocouple pasted to the side of the AGM battery in the canopy - temperature was rarely more than ambient, which I figured was good for the battery. But the Remco AGM died within 3 years despite an easy life and never being discharged below 12.0V. I put its relatively early death down to my good wiring which allowed anything up to 45 amps into the battery after startup. I expect if you use an AGM under the bonnet, you'd want to limit the charge current - just wondering whether you have a way of doing that?
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Follow Up By: Allan B (Member, SunCoast) - Tuesday, Jan 10, 2012 at 22:21

Tuesday, Jan 10, 2012 at 22:21
Hi Phil, Each of my two AGM's are now charged via Redarc BCDC1220 charger/isolators which not only limit the charge current to 20 amps but also are 3 stage charge. I am hoping that this scheme will not only recharge the batteries in optimum time but will also maximise the battery life.

One battery is dedicated to the fridge and the other supplies all other auxiliary loads.

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Allan

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Reply By: Dennis Ellery - Monday, Jan 09, 2012 at 22:29

Monday, Jan 09, 2012 at 22:29
You’ve got 6 cylinder Troopy - I've measured mine, a V8 Troopy, and the rear of the engine bay reaches 80 deg C – I will only use maintainable wet batteries under the bonnet of my vehicle.
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Follow Up By: Allan B (Member, SunCoast) - Monday, Jan 09, 2012 at 23:58

Monday, Jan 09, 2012 at 23:58
Yes Dennis, I'm sure the temperature would reach much higher under higher ambients and heavier loads. Maybe the V8 helps too!

We crossed the Simpson last mid-November and the air conditioner was struggling because of 40c ambient and low forward speed, so I'm sure the engine bay temp was way up too.

I run an AGM in the cabin and until recently also a flooded deep cycle in the engine bay (plus the cranker) but needed to replace the deep cycle and thought to try an AGM which spurred me to shield the batteries. Time will tell.

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Allan

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Follow Up By: Member - Frank P (NSW) - Tuesday, Jan 10, 2012 at 10:42

Tuesday, Jan 10, 2012 at 10:42
My 2nd battery in my D4D Prado is in the engine compartment. The battery management system stops charging when battery temp reaches 50 degC but continues to record max battery temp - highest observed is 63. I suspect it's gone higher than that but I haven't observed it. Scary when you think about all that hot acid.

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Frank
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Follow Up By: Dennis Ellery - Tuesday, Jan 10, 2012 at 11:58

Tuesday, Jan 10, 2012 at 11:58
In ambients in the 30 to 35 deg range my 1st battery runs at about 63 and the 2nd at about 65 deg c – On one occassion the 2nd battery reached 68 deg (glass thermometer dipped into the electrolyte).
AGM manufacturers won’t guarantee their batteries at these temperatures so I don’t use them under the bonnet.
Regards Dennis
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Reply By: Wayne (NSW) - Tuesday, Jan 10, 2012 at 06:10

Tuesday, Jan 10, 2012 at 06:10
Allan,

Good idea about the heat shield. I have looked at trying to reduce the heat under the bonnet of my 78 Series. I have looked at fitting vents over the batteries, but this has proven to be a big exercise.

What I have come up with, and a few have done it in the past and that is to raise the back of the bonnet using a spacer under the hinges.

The wife has a nylon cutting board, about 10mm thick, I was thinking of buying her a new one (her birthday is coming up soon), so I will cut it up to make spacers.

The only problem that I can see with your idea is when you have to change the oil filter the heat shield will probably be removed and replaced again. Minor point but if the batteries last longer well worth it.


Wayne
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Follow Up By: Allan B (Member, SunCoast) - Tuesday, Jan 10, 2012 at 08:30

Tuesday, Jan 10, 2012 at 08:30
Hi Wayne,

I had earlier considered the scheme of raising the back of the bonnet but when you look in the engine bay there appears to be plenty of space for the air to flow down past the firewall as it is being forced by both the fan and the ram effect. I really doubt that opening a narrow slit along the back of the bonnet would make any appreciable difference. I considered it more important to shield the batteries from the engine radiant heat and to have cool air, rather than air via the hot radiator, pass over the batteries. Furthermore, there is potential to get oil deposited on the windscreen with that scheme.

The idea of raising the rear of the bonnet seems to be a notion only. I wonder if anyone doing it has actually measured before and after temperatures of the batteries.

Incidentally, I used a couple of thermocouples positioned in the engine bay to measure temperatures with the vehicle in motion.

The shield in my vehicle does not appear to obstruct the oil filter removal and being flexible is an advantage.



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Allan

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Reply By: Andrew - Tuesday, Jan 10, 2012 at 10:33

Tuesday, Jan 10, 2012 at 10:33
Lifting the back of the bonnet works on some vehicles but not on others. The effect can change with vehicle speed as well.
The area in front of the windscreen on most vehicles is a high pressure are so that air can actually be pushed into the engine bay from there with the effect getting worse as the speed rises.
There is a famous case of an old (very old) English sports car that kept overheating: they started measuring the airflow and found that the high pressure at the rear of the bonnet where they had vents fitted was taking in air and pushing it out backward through the radiator.

So if you do lift the back of the bonnet it will be worth doing some before and after testing to make sure the result is what you want.

At low speed (below say 50kmh) the effect is much less and it may be beneficial.

feeding air out through vents in the guards would normally be more effective as this is not a high pressure area.

The other thing to remember is that you still need air flowing past your exhaust to prevent it overheating the engine bay so any mod you make needs to take that into account.

regards

A
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Reply By: Gnomey - Tuesday, Jan 10, 2012 at 15:36

Tuesday, Jan 10, 2012 at 15:36
G'day Allan
Nice work. Like it a lot. Very useful idea for my troopy and like Bob have some aircel insulation hanging about. Thanks for posting mate.

Cheers
Mark
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Follow Up By: Member - Phil G (SA) - Wednesday, Jan 11, 2012 at 07:04

Wednesday, Jan 11, 2012 at 07:04
I wouldn't use Aircell - the foil could easily create a short around the batteries.
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Follow Up By: Allan B (Member, SunCoast) - Wednesday, Jan 11, 2012 at 09:29

Wednesday, Jan 11, 2012 at 09:29
Phil, my insulation is also foil covered however as can be seen in my photo the battery +ve terminals are fully shrouded. In addition the foil area near the battery posts is covered with a couple of layers of gaffa tape as further insulation. Furthermore, the insulation stands away from the battery and it would be necessary to push the insulation panel in order for it to contact the battery post.

Nevertheless, your warning is appropriate and precautions need to be taken against electrical contact.

Cheers
Allan

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