Aux battery voltage in very hot weather

Warren-Pat_01 · Guru

Aux battery voltage in very hot weather

Whenarewethere · Guru

My battery is at the rear of the engine bay, but it is entirely closed off from the engine also with rubber gasket, I think also for water proofing purposes, & the battery has air movement at the rear.

Can you build an enclosure around the battery with an air gap & air access away from the engine & cover this enclosure with some aluminium coated engine bay insulation. It will put a really good barrier between the engine & battery.

I have 2 of 3 26AH auxiliary batteries under the passenger seat. The only space I could find in the car, but at least the batteries stay at room temperature!

We generally sleep in our car & in hot weather we open the bonnet to get the car to cool down quicker.

Aus-Kiwi · Guru

Shielding and open to fresh incoming air helps big time . E series falcons have a plastic box and vented I often use on extra battery .

rockylizard · Guru

Gday...

Finally, at least there is something that Land Rover have done proper then by that advice ... both batteries are in the engine compartment and clear from the engine and have fresh air directed around them. Original main battery lasted 8 years ... and the current main battery is 4 years and perfectly good. Original aux battery lasted 7 years and the replacement has now been insitu 5 years ... and perfectly good.

I know no-one will find any of that believable - let's face it ... LR are not acceptable as vehicles as they defy physics.

Cheers - John

Peter_n_Margaret · Guru

Charge rate is also affected by the temperature of the battery.
With the same charge setting, higher rates of charge will occur in warmer conduitions and lower rates in colder conditions. That is not ideal and can lead to over charging when hot and slower charging when cold.
To compensate for this, good quality chargers have a temperature monitoring probe which is attached to the battery and they will then increase or decrease the charge voltage accordingly.
If you want to get the best life and performance from your battery, choose a charger (or solar controller) with this capability and fit the probe.
Some have temperature compenstaion built in, but that is a compromise that might not be ideal if the battery is seperated from the charger/controller. One with a probe is preferred.
Cheers,
Peter

Warren-Pat_01 · Guru

Hello everyone,
Some things I didn't include with my first query.
1. The battery fitted has been in for just over 12 months & is still going (?). Past batteries have lasted up to 12 months.
2. I have a shield around two sides (engine side & back) leaving the front open to receive the nominally hot ambient temperatures.
3. The shield is plywood painted with silver/aluminium paint & 10mm silver sided foam insulation - the same foam is under the battery.
4. The CETEC DC-DC charger has a temp probe but to get some charge into the battery, I have placed it just behind the front panel where it gets some air. Mounting it as instructed near the +ve terminal gave me NO charge into the battery. I realise I could be exposing the battery to danger.
5. The CETEC is rated to 60 degrees which is why I installed it behind the grill - not on the firewall where the "experts" suggested.

After a hot day's run, I lift the bonnet & put a wet rag around the battery - it seems to help restore the terminal voltage & the fridge runs ok.

Pat is on my back as I continue to suggest that my next car will be a dual cab (D-Max) - "I don't want to drive one of those to the shops", "The ride is too hard", "There is no room in the rear of the cab", etc. I've said that the seats are the same as the MUX, the ride in the new ones have been softened, AND the aux battery will be in THE BACK AWAY from the engine. Friends have a MUX - to change the fuel filter, they have to take the aux battery out!

I'll get in touch with Forbes - the supplier of the battery tomorrow & see what they suggest.

Whenarewethere · Guru

Even though you have covered the battery with insulation is it actually getting ambient air, or is the air somehow circulating from the engine bay at a too higher percentage.

My Waeco fridge was recirculating air around the side of the fan due to basic poor design. I installed a baffle so air comes in one side of the fridge & 100% of the hot air goes out the other side.

Mike Harding · Guru

Is the battery an AGM? Probably is my guess.

With the exception of Optima (who use a different construction technique) no AGM I have ever encountered is suitable for under-bonnet use *despite* what the dealer, as opposed to the manufacturer, may say. In general AGMs are speced. for around 55C maximum working temperature. Under-bonnet temperatures are much higher than that.

Warren-Pat_01 · Guru

G'day Mike,
It is an AGM (SSB brand). I checked at the dealer today - they put me on to a website called The Battery University (cannot save it as a favourite for some reason).

Basically it is HOT (at a guess, I'd say something like 120C) under the bonnet on a hot day. I just have to find some way of pushing "cooler" air around it or cool it down with a wet rag after a run. Will also look at adding slots in the guard skirt.

John (rockylizard), the batteries in my first Patrol (MQ) lasted 7 years but then that car had less stuff under the bonnet, no turbo & was 24v - gentle on batteries. Troubles due to heat were rare.

Jon, it would still get a small amount of hot radiator/air cond air over the top.

Thanks to everyone else for their inputs.

Whenarewethere · Guru

Can you run a bit of, say 50mm ducting, lightweight flexible pipe, to the front of the car to feed some outside air to the battery environment. You don't need to force feed truckloads of air, realy just to gently push engine bay air out of the battery.

Warren-Pat_01 · Guru

I'd like to Whenarewethere.
I'd also like to upgrade the bulb in my LHS headlight too (as I did the RHS one a couple of years ago) but there ain't any room & being on blood thinners makes cuts & scratches even worse. When & if the bulb blows, I'll have to do some dismantling to gain access!

I'll just ensure that after a day of driving in hot weather that I'll pop the bonnet & cool the battery with a wet rag. Tomorrow is going to be a fair bit cooler to travel north. We had no option a couple of weeks ago when the temps were in the mid 40s.

Whenarewethere · Guru

Force air into the battery environment from somewhere else with a fan?

PeterD · Guru

Warren-Pat_01 wrote:
Is there a chart available that shows batt volts, battery capacity vs temperature?

There is a lot of white noise above but I don't se where your question has been answered. I have looked around and I can only find charts for electrolyte temperatures up to 100 Fahrenheit. Open Circuit Voltage (OCV) vs. Temperature

denmonkey · Senior Member

I'm glad someone else has noticed this W&P during this hot weather we've been having.

My Aux AGM is in the spare seat well over the back of the pajero.
Even though, it's well shaded, I reckon on these 40+ degree days we've had, the temps inside the car sitting in the sun must be near double that.

My waeco has been going into error because of the ambient heat in the car.
Like you I've seen the voltage on my aux battery suffer and struggle to keep up even with the more than enough solar going in.
It's just not taking the charge.
I disconnected everything from it and gave it a rest for a few days.
Seems to have bounced back a bit.

A mate even went as far to take his new 95L waeco back into the shop due to similar problems.
Of course it came back all ok.

I think it's just too much of an ask for both the batteries and fridges to keep up in those conditions.

cheers Brett

Warren-Pat_01 · Guru

Thanks PeterD for the link. Along with the link that the dealer handed on (the Battery University), there is a lot to absorb.

Brett, we struck "cooler" weather on the way home (up to an ambient 33 degrees, down to 28) so the battery performed a little better & even kept the fridge going well. I'm not convinced that I lost any charge while the battery was hot & the voltage reduced - I think the correct charge was doing in but the battery compensated itself to reduce the chance of an explosion. When the battery was cooled down, the terminal voltage was correct & the fridge ran ok without needing the engine being started.

I wonder is a good invention might be a Eutectic (like the Autofridges had a few years ago) battery case with the aux battery inside to keep the battery cool???? It might earn someone a few $$$$!

PeterD · Guru

Hot temperatures effecting the fridge running? Have you considered the effect of temperature on your solar panels? The following graph shows how solar cells/panels drop their guts as they heat up. If the airflow around the panels is poor (good gap underneath) their output voltage drops. If it dropped too low you may not have been getting a full charge into your battery.

Solar panel performance with changing temperature..jpg