What is all the fuss about fuses?

12 volt fuses

Sure, I understand the importance of fuses when installing 12-volt products in my 4WD, I have always done whatever the installation notes tell me. However, in a moment of haste, I missed one crucial sentence when installing a new brand of voltage sensitive relay (VSR) in my engine bay. I’m just thankful that what eventuated happened in the driveway and not in one of the remote locations I’d just returned home from.

It was one week to go….

Until I left on a four-month adventure. My existing VSR wasn’t working, it was not engaging when the main battery reached 13.4 volts. I reached out to Projecta, one of my sponsors. Thankfully, a VSR200 arrived in my letterbox within a couple of days and I quickly replaced the VSR ‘plug and play’ style.

Projecta VSR200

This was the Projecta VSR200 that I installed…incorrectly

Home again

Over the next 25,000km, I had no issues with my auxiliary battery receiving a charge. Having returned home, the Prado sat quietly in the carport for the next few weeks as I busily got on with writing and submitting travel articles to editors.

One morning I went to start my 4WD, but nothing happened. No ticking from the starter motor, no lights flashing on my dash, just absolute silence. My main battery was flat, thanks to a damaged cell most likely caused by the vibrations from all the corrugations I had driven.

Not to worry, my camper trailer had the same batteries and configurations that were in the Prado. I swapped out the damaged battery but unfortunately, this battery didn’t have the charge left to crank the engine. My 10amp 240volt battery charger was hooked up to the main battery and left to charge overnight. I expected to be able to start the engine without a problem – I was wrong.

Supercharge Allrounder battery

My starter battery was giving me grief

Next morning, the battery was still cactus. I contacted the RACV and when the tech arrived, he confirmed that the battery was sick. He was able to jump start me and advised that I should run the vehicle for 45 minutes to let the alternator inject some charge. I ran it for an hour, switched off the engine and held my breath. I turned the key in the ignition. Nothing.

Frustrated, the battery charger was reconnected to the main battery and I went inside to find a replacement battery online. What happened next still haunts me.


I walked out of my office towards my kitchen when I noticed the smell of burning plastic. I glanced out the back door to see black and grey smoke spewing from under my bonnet. I raced out the back door and switched off the charger at the power point. Next, I gingerly raised the bonnet, knowing there was a risk of a backdraft increasing the intensity of the fire. I ripped the alligator clips from the battery and ran to the passenger door of the Prado, tearing the fire extinguisher from the cargo barrier.

fire extinguisher

Thankfully my extinguishers are easily accessible and ready to go

A quick shake, pull the pin, then point at the flame and pull the trigger. White foam spewed from the little red extinguisher all over the VSR as it spat sparks and flame. With the flame quickly extinguished and the little red bottle empty, my next task was to stop the fire burning behind the sound deadener under my bonnet. Thankfully my dog’s water bowl was within easy reach and I splashed water over the smouldering area, halting the burning.

Engine fire

It is a mess, but I was very lucky not to have lost the lot.

What a mess! Foam everywhere, the smell of burnt rubber and plastic, but the danger was still there. The VSR was still sparking as charge flowed from my batteries. I wasted no time in disconnecting the positive and earth cables from both batteries, just to be safe.

It was then the shock set in. What if I hadn’t walked out of my office at that exact moment? What if the bonnet was fully closed? What if the Prado doors were locked? I would have lost my carport and garage; most likely my neighbours’ garage would have been hit hard too. Most of all, what caused the fire?

The Wash Up

It was obvious, with the damage it suffered, that the VSR was the origin of the fire but why? I contacted Projecta and within minutes I was talking to a technician on the phone. After explaining the back story, we concluded that the main battery was most likely the problem.

Projecta VSR200 Installation notes

Projecta VSR200 Installation instructions. As you can see it is noted that fuses be installed for safety reasons.

With at least one dead cell, it was spitting current at the VSR via 4 B&S cables, especially when connected to the battery charger. The VSR is designed to handle 200amps continuous with a peak of 400 amps but it is also designed to have a fuse connected between the main battery and the VSR. This is the one step I had missed in the rush to swap out my old VSR. A big mistake it turns out, but hindsight is an amazing thing. I turned it into a valuable lesson and learnt a lot from it.

I decided to re-evaluate the wiring I had installed throughout the Prado. Now I must say, I have always used the correct size of cables for all my wiring. Old wiring was replaced with new, a new fuse box was installed, old circuit breakers were removed and replaced with 50amp ANS fuses and most important of all, the VSR was replaced with a Projecta IDC25.

Being an automatic 25-amp 3 stage DC/Solar battery charger, I know that my auxiliary battery is now receiving a safe and comprehensive charge. The IDC25 also allows me to have a different type of battery (AGM, WET or Calcium) to the main battery, something I couldn’t do when using a VSR or isolator. I have also installed 50 amp ANS fuses between the main battery and the IDC25 and between the IDC25 and the auxiliary battery.

I was very lucky and had I read Projecta’s installation document correctly, the fire would not have occurred. So, what is all the fuss about fuses? Without them, you are leaving yourself open to disaster.

Prado, Toyota, Landcruiser, 120 Series, Projecta

The finished product

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