Outer Limits 4x4 Board

G’day All,

I have a 98 Jack 3.0TDi which I’m absolutely in love with except for a few niggly problems.

The main one is the auxiliary battery location (left side @ firewall) which gets awfully hot. On average I go through a battery (70-80Ah sealed lead acid) every 8-12 months because of excessive under bonnet heat. The battery runs my fridge, LED reversing lights, LED roof mounted emergency strobes, radio/cd hifi system and 2 x CB radios.

As I use my car a lot in the summer and especially with disasters like Black Saturday along with high ambient air temperatures, one can only imagine how hot it gets under the bonnet especially with the turbo screaming its lungs out.

I am now thinking of installing a 40Ah AGM in the tray and covering it in 50mm polystyrene foam as a heat sheild with a second battery around 40-50Ah inside the car at the rear complete with VSR isolator to run my fridge and reversing lights/work lights. Unfortunately I can’t just have a large battery in the cargo area due to the amount of equipment I carry when doing disaster work.

I can’t keep buying AGM or similar sealed type batteries every 8 months or so as it’s getting rather expensive.

Any one got any suggestions on what I should do?

I’m praying someone has a solution as the problem is driving me nuts.

Thanks.

Firstly, I would change battery style to an open style re-fillable battery, to just keep the water levels up. The 'sealed' types are more than likely drying out as they vent under the high temps, but the liquid level cannot be topped up.

Second, there was a thread on here within the last 6 weeks or so I believe that offered all sorts of suggestions regarding battery heat shields under bonnets - I think there was a perforated exhaust wrap materal used with success. I have used straight sheets of aluminium sheet with 12mm airgaps to solve a heat transfer problem with a battery mounted next to a turbo - works well.

Third, are you able to transfer your batteries to a new location say under the tray, but still accessable to service? If so, you could build a very nice insulated box that is only going to see ambient heat loads. The insulation alone is not enough - as it just slows down the temperature rise - you need to vent the box and I would do this with a small blower - heaps around - bilge vent blowers are great for this, draw small current and shift heaps of air, 80mm dia x 150 mm long, all plastic.

Hi tektrek, as PBBIZ2 posted, you need to fit a flooded wet cell battery.

MOST AGMs are not designed to be fitted under the bonnet and it's not just the heat thats the problem.

With the battery so close to the alternator, the voltages being applied to the battery are too high and a combination of high temps and high voltage, which means high current as well and your AGM hasn’t got a chance.

If you fit a flooded wet cell battery, it will tolerate all the above, they are designed to while most AGMs are not.

If you mount an AGM elsewhere, then the cable running between your cranking battery and your AGM will act as a voltage/current regulator, plus because the battery is not in the engine bay, it will be much cooler and this means it can actually tolerate slightly high voltages and this all combines to help your AGM last much MUCH longer.

I have decided to install a flooded wet cell, non-maintenance free type so that I can top up the cells from time to time with demin water.

By the way the voltage from the regulated charging circuit is not high as it is regulated (duh!) to 14.4-14.7vdc max although some do go as high as 15vdc. The maximum recharge voltage by the way of any lead acid battery (sealed, unsealed, AGM etc etc) is 14.7vdc @ 20degC which is at the edge of gassing. The charge voltage does not need to be current limited as found with NiCd, NiMH, LiION, LiPO etc nor do they require any delta charge intelligence.

Lead acid batteries will accept as much current (ie Amps) as they can get - this being limited by the size of the alternator or battery charger or solar/wind gen system. AGM lead acid batteries as a rule will accept higher recharge voltages hence quicker recharge times as opposed to lead acid wet cells. On the otherhand, flooded NiCd cells and NiFe flooded cells will cope with even higher voltages with some NiFe cells doing away with regulation altogether.

The nominal ambient temp range of flooded wet cell lead acid batteries (PbSO4) is generally in the range of 15-65degC irrespective of brand. Common AGMs will go to 60degC with some higher priced versions going up to 70degC. The military ones I have been using go up to 80degC

As the mil-spec AGMs I have been using are OK up to 15.5vdc they can't handle ambient heat beyond 80degC hence my original post about heat insulation.

If I want to stick to a sealed type auxiliary battery in the engine compartment I could get the latest lithium ion but at around $1100 for 2 x 12v 40Ah in parallel it’s getting a bit too expensive.

So, until such time the prices drop on the lithiums I’ll be using conventional lead acid wet cells.

Best temp for lead acids is 20-25deg C. Once over that temp the loss of life expectancy is fairly linear to the temp increase. From memory its about 1 year for every 5 deg above 25....dont quote me on that just yet as I havent got my info here. In any case keeping the batteries cool is a good idea.

Not sure if you have considered bonnet venting ( or scoop). At least if you can get some ambient air in it would be better than radiated exhaust heat. My old AGM has just died and its 5 years old and being stuck next to a turbo, but under a bonnet scoop, its probably not too bad.
http://ssv.com.au/bonnet_vents

Some exhaust lagging might help too. Helps with boost as well.
http://www.horsepowerinabox.com/HPIAB2/category60_1.htm

Wet cells are good, but if you plan on corrugated roads or steep high country, you may end up with acid spot burns under your bonnet like I have.
Gel cells will die even quicker than your AGM's.

Under the tray is ok (protected from stone and stick damage of course), but its a Jackaroo - isnt that a wagon?

NiCD are brilliant, and will last you a good 15 - 20years under the bonnet, but the cost will be significant. Only down side is if they go flat, they are like a dead short and need a current limited charger to kick them back to life.

I think the best solution is to vent it and shield it as the others have said

Thanks for your reply clanky.

Re

Best temp for lead acids is 20-25deg C. Once over that temp the loss of life expectancy is fairly linear to the temp increase. From memory its about 1 year for every 5 deg above 25....dont quote me on that just yet as I havent got my info here. In any case keeping the batteries cool is a good idea.

You’re pretty much spot on with that estimate. As for ambient temp the max for most flooded cells is 25deg but from experience this is dependent on cell construction and materials used, i.e. some standby deep cycles are rated to 30degC.

Not sure if you have considered bonnet venting ( or scoop). At least if you can get some ambient air in it would be better than radiated exhaust heat. My old AGM has just died and its 5 years old and being stuck next to a turbo, but under a bonnet scoop, its probably not too bad. http://ssv.com.au/bonnet_vents

Some exhaust lagging might help too. Helps with boost as well. http://www.horsepowerinabox.com/HPIAB2/category60_1.htm

I had a look at the 2 links but I don’t particularly want to cut another hole in the bonnet as the intercooler scoop takes up a lot already. As for lagging that has some merit and that was something I thought of doing but around the battery itself which is lot easier to access. I am currently looking at aluminiumised fabric (looks kind of like the stuff used in a silver airport firefighter suit) and also silicone impregnated fabric which are both used in the fire industry for heat shielding of windows, pumps, generators etc in bushfire prone areas.

Wet cells are good, but if you plan on corrugated roads or steep high country, you may end up with acid spot burns under your bonnet like I have. Gel cells will die even quicker than your AGM's.

I’m hoping my fabric thermal coat will overcome the spot burn problem as all faces of the battery except the underside will be covered. As for immobilised gel electrolyte (true GEL) cells they are great in high vibration areas but I gave up on them years ago as they sulphate at the drop of a hat no matter how well you look after them and they cost nearly twice that of a heavy duty wet cell.

Under the tray is ok (protected from stone and stick damage of course), but its a Jackaroo - isnt that a wagon?

Yep, sure is, like a patrol/cruiser/pathfinder etc.

NiCD are brilliant, and will last you a good 15 - 20years under the bonnet, but the cost will be significant. Only down side is if they go flat, they are like a dead short and need a current limited charger to kick them back to life.

Nickel Iron (NiFe) even go longer than 20 years and only need a water top up every 5 or so years. Some of these from world war 2 are still going as strong as the day they were made. If boiled dry you just need to refill with distilled water and charge for 2 cycles and they are as good as new but they cost up to 5 times that of a similar sized nicad wet cell which is 3 times the cost of a similar sized lead acid wet cell.

I will try lagging a smaller AGM and hook it up to another larger AGM near my fridge. Both batteries will be isolated with voltage sensitive relays for isolation from the main battery. If the idea works I will post my findings on this forum.