Thank you Spruce and Rosskesava
Good points raised by you both. I will try to cover them as best I can
To Answer Spruce,s point all our controllers for some time have had a reverse polarity diode fitted on to the PCB. It is placed so we can protect the pump driver, majority of the circuits and processor from reverse polarity.
We also recommend and supply the appropriate fuse and holder to be fitted on the Positive lead (red) between the battery and control.
As Don points out fitting the fuse can help protect the controller and diode in the event of reverse polarity. For this reason on the bottom of all the installation guides we state.
1. Make sure correct fuse is fitted inline. Failure to do so will result in damage to the unit.
2. Observe correct battery polarity. Failure to do so will result in damage to the unit.
As Spruce pointed out yesterday in another post the fuse should be fitted as close to the battery as possible to protect the wiring after the fuse. The most likely cause of a power spike or short is from the power source (battery). Hence the less distance the short can travel between source and fuse the better.
It is also for this reason we do not pre fit the fuse but supply a kit.
The following link gives a little more detail
http://www.springltd.co/node/136To cover the suggestion by Rosskesava fitting a lager diode to offer higher levels of protection is an option. However larger diode would generate more heat and make the unit less efficient. To counter this would require us to fit larger heat syncs, FETS together with upgrading the copper tracks on the PCB. The result would be a larger unit which would also increase the cost of the unit.
The Controls are supplied with 1mm Tri cable rated to 18amps. The control itself is rated to 10 amps. We also fit an over current protection circuit on to the PCB so if the unit see,s a sudden spike in current it shuts down the pump to protect itself.
In effect then we provide three levels of protection
1. Reverse polarity diode
2. Supply and recommendation to fit a fuse
3. Over current protection
It is a discussion I have with my MD and Tech director from time to time. When we look at numbers of controls returned due to blown reverse polarity diode it is a tiny fraction of what we produce. We look at a balance between trying to provide as much protection as we can while producing an efficient control at reasonable cost.
When compared to the 1000,s of units we produce we might see 50 or 60 a year. Because the diode is fitted we can repair the control, which we do for a small charge. If we can not be sure what has caused the failure and the control is within its warranty period we give the user the benefit of doubt and repair under the warranty.
From what we see the issue of reverse polarity damage to controls is diminishing this is in large part thanks to greater awareness raised by cleaners themselves.