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Author Topic:   Crossed-wired the Battery
prpark posted 04-21-2013 05:20 PM ET (US)   Profile for prpark   Send Email to prpark  
Today, I crossed the terminals and hooked up negative to positive and vice versa [on a Boston Whaler boat model 170 MONTAUK]. Each terminal sparked when I attached, and as I was not paying attention, I noticed the radio did not work. I disconnected and reconnected and the [radio] seems to be dead.

What are the procedures to see if I have done permanent damage? I pushed in the main and bilge breakers, what next? Thank you, in advance, for your help.--Phil

jimh posted 04-21-2013 10:37 PM ET (US)     Profile for jimh  Send Email to jimh     
Phil--You have reversed the polarity of the boat to the battery. See the prior discussion on precisely this topic:

Reverse Polarity to Battery

jimh posted 04-22-2013 08:46 AM ET (US)     Profile for jimh  Send Email to jimh     
Check for fuses that have been blown. If you are lucky a few fuses have blown and protected the devices downstream.

It used to be common in DC-powered devices for the input power circuit to have a large diode wired across it to ground so that if the polarity were reversed the diode would be forward biased. This would result in a very large current flow, which, if the device were properly installed with the correct value of fuse protecting it, would just result in blowing the fuse. This reverse-polarity protection diode was usually sized to be able to handle a lot of short-circuit current, so it would outlast the fuse. Whether or not devices on your boat have that sort of protection is not known.

Some DC-powered devices have the input power circuit wired to a full-wave bridge rectifier, so that even if the applied power has the polarity reversed, the diodes in the full-wave bridge rectifier straighten out the current path. Nothing bad happens to devices like that when the polarity is reversed. Whether or not devices on your boat have that sort of protection is not known.

If a device has no reverse-polarity protection, it might draw a high current when its power source is connected with reverse polarity. If there is no fast-acting fuse to protect the device, the high current might cause damage to the device. One unfortunate aspect of solid-state devices is their intolerance of momentary overloads. They often fail catastrophically when the current flowing through them exceeds their maximum rating, even if only for a very short time.

jimh posted 04-22-2013 08:52 AM ET (US)     Profile for jimh  Send Email to jimh     
For over-current protection, fuses generally operate faster than circuit breakers. This is an advantage in favor of fuses. They might blow fast enough to save some expensive electronics from being ruined.

Again, the recommendation to clearly mark the battery cables and the battery terminals for polarity with color vinyl tape is most strongly made. Here is another instance in which confusion about battery cables may have caused damage to a lot of costly electrical and electronic components.

prpark posted 04-22-2013 09:08 AM ET (US)     Profile for prpark  Send Email to prpark     
jim - Thank you for the reply and the link to the reverse polarity post. I will follow up based on your input and ensure the cables and battery terminals are clearly marked.
L H G posted 04-22-2013 12:51 PM ET (US)     Profile for L H G    
I don't know which engine you have on that 170, but it would either be a 2-stroke Merc 90 or a 4-stroke "Mercaha" 90. You had better check the engine and see if runs. There is high probability you blew out the engine's rectifier. Look for an erratic tach signal.
jimh posted 04-22-2013 05:21 PM ET (US)     Profile for jimh  Send Email to jimh     
Please see the prior discussion for information about the damage to the battery charging circuit of the outboard engine. That topic is discussed in detail in the prior thread.
prpark posted 04-23-2013 01:10 PM ET (US)     Profile for prpark  Send Email to prpark     
Please confirm that to reset the breakers on the "black box" (DC Main and Bilge) and on the helm, that I push in the rubber covered breaker?

Thank you for your help.


davej14 posted 04-24-2013 05:06 PM ET (US)     Profile for davej14  Send Email to davej14     
Yes, to reset the breakers you press in on the rubber covered reset button.

Hope that damage is minimal, you will be very lucky if the rectifier on the engine is not damaged.

It seems like every couple of years we see this happen. I don't recall who exactly made the comment but it was something like "most people only make this mistake once".

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