Reverse polarity occurs when you jump start your car or when you install new batteries. Polarity is a result of an “accident,” but the effects can be damaging.
Nowadays, much of the gear that can be bought in the marketplace may be damaged by polarity because of poor design techniques.
The Culprit: Poor Equipment Design
There is an area in design where manufacturers are often at fault. It’s an ongoing trend in their design. It seems like 12-volt and 24-volt electronic equipment are more prone to damages. It is a bit ironic because most equipment is designed with some form of reverse polarity protection. This is usually in a diode and fuse form.
This is the theory: if reverse polarity occurs, the designed diode will then conduct and short the power supply in order to ground and trigger the fuse to blow up. This protects your equipment. This should work well if the equipment has been designed properly.
Unfortunately, there is a disturbing amount of 12-volt and 24-volt electronic equipment with this design flaw. They make the copper traces on the printed circuit board extremely small. Unfortunately, this then pulls a lot of current through the diode in order to pop the fuse which then vaporizes the printed circuit board power trace. Once this happens, you will then need to replace the whole board or have it repaired. In either case, this will require expensive repair.
Can Battery Reverse Polarity?
Yes, it can, but it can happen only in two ways. First, if you are filling it up for the first time. If you use an old type of charger, you can short the terminals. You could be hooking up the charger backward and end up reverse charging your battery. You won’t see a spark because the battery actually gains voltage while you charge it. The short won’t be enough to create a spark
You can also reverse the polarity of a battery after you’ve activated it. This is rare, but it is possible. In order for this to happen, you will need to perform a sequence of errors that would eventually trigger the reverse polarity.
The only way to discharge the battery completely is by failing to notice a dead short that will eventually dissipate the battery charge. After some time, the battery will be discharged entirely. But in order to have a negative charge, you will need to hook it up backward and charge it again. So, the only way for a positive-charged battery to reverse itself is to discharge completely, and then reversed charged.
But Can a 12-volt Battery Reverse Its Polarity?
Yes, it can happen. If the battery cells are out of balance, some cells will discharge before the others. As it continues to discharge, they will start to reverse polarity. Now, if there is an external factor that keeps the current from flowing, like for instance, when the batteries are in a series, and then one goes bad, the battery will start reversing polarity on some or all of its cells. It doesn’t really get that bad in an installation if there are no external errors or mistakes that lead to the reverse charge.
To really keep your battery in tip top condition - you will need a industrial grade professional battery maintainer such as this one from NOCO.
13 comments
As Bob said above "Iv’e been a mechanic on airplanes, boats, tractors and cars for 50+ years. I recently replaced the starter on one of my compact tractors. The result had me puzzled for weeks. Instead on engaging the bendix the starter just spun. Battery voltage showed 12.7v. A consensus proposed reversed polarity which I thought was unlikely. Then test meter positive probe to the main cable from the battery to the starter and the negative probe to the body of the starter showed -12v! Another battery was installed and the test showed +12v at the starter and the starter engages in it’s normal fashion! Now with the battery on the bench, the test probes in correct position, the reversed polarity shows up that this battery has become reversed! IOW the 12v positive post is now negative!
1957 Jaguar XK140. Positive earth. I installed a new aluminum radiator with a newer electric fan. Also an electronic thermostatic unit to control the fan was installed and has a POT to adjust the fan to the temperature desired for fan activation. Wired using diagram and connected ING + to vehicle’s NEG. hot, the same with constant hot.
Would not work. Fan would only work when relay was removed from this controller unit and a jumper was inserted between 30 and 87. The fan pushed instead pulling. Easy enough to correct by reversing the two fan wires.
But no thermostatic function from the controller. Then the unit smoked and burned. Are there any devices available to reverse polarity in just this circuit?
There is another way to reverse a battery, common to 24V trolling motor setups. In this scenario, two 12V deep cycle batteries are connected in series to create 24V. That is Battery 1 negative is connected to Battery 2 positive, while Batte try 1 positive and Battery 2 negative provide electrical service to the motor. If left to discharge, one battery may fully discharge before the other. If the mother is left attached (it will pull a tiny amperage even if off), the weak (but still live) battery will reverse the polarity of the dead battery. Lesson: Disconnect the trolling motor and install a switch between the two battery connection when not in use.
I have a near new 24v battery and changer for a lightweight grass strimmer.
I’ve been told I have cross polarity.
How do I completely discharge the battery and fill again ?
i tried to jump start a 2015 Nissan and hook the cables up backwards on the Nissan. it started to smoke and spark flew. had to buy a new battery but it would not start or do any thing. what can i do to fix this