Hello Kevin,

A while back you gave me some great advice about installing a VSR on my boat to charge three batteries on a two bank charger. It has been working perfectly. Thank you.

Here is a brief scenario of what I’m doing now:

I’m preparing my boat wiring for “mini season” (florid lobster). We go bully netting at night which if you are not familiar with it, you basically drive around on shallow grass flats and net the lobsters from the boat.

What I have done is made a PVC rail which has three pipes which will hold three or six light bulbs underwater. I have tested with 12 volt, 50 watt lights and they seem to work fine but they don’t given much light. I found that they do have these light bulbs (look like regular house bulbs) in 12, 24 and 32 Volts, up to 100 watts.

My question has three parts.

1) I plan to power them from my trolling motors 24 volt system, plugged directly to the tolling motor plug. Can I use 75 watt, 32 volt bulbs or should I use 100 watt, 24 volt bulbs? My understanding is that the higher the voltage the longer the batteries will last.

Kev says…

The voltage rating on the bulbs is the maximum operating voltage that they should be connected to. The wattage rating is how much heat/light they will give off. At their rated voltage, the 1000 watt bulbs will be considerably brighter. Since you are operating at 24 volt, the 32 Volt bulbs would only be operating at 75% of their capacity or 56 Watts. At 24 volts, the 1000 Watt bulbs would be nearly 20x brighter.

2) How long should I expect two 12 volt, i.e., 24 volt, Group 27 batteries to keep these lights on? The 75 watt bulbs will draw just over 2 amps each. The 1000 watt bulbs will draw just over 41 amps.

Kev says…

If your batteries are rated at 100 amp hours each, one of the 75 watt bulbs would last about 100 hours, two would last about 50 hours. Similarly, one of the 1000 watt bulbs would last 5 hours, two would last 2.5 hours. etc

3) Will it be OK to run a portable generator on the boat and keep it plugged into my onboard charger? I’m not worried about wetting the generator as this is done at very slow speeds, my concern is damaging my electrical system.

Kev says…

My primary concern while running a portable generator would be the AC ground. Unless your boat has a complete shore power system with a 30 amp or larger inlet, this connection probably doesn’t exist. To make it safer while running your generator, I would connect the AC ground on your generator (maybe a chassis ground) to the DC negative system on your boat. This will trip your generator output breaker if you have any type of fault in the AC system

Kevin thanks for your reply, this helps tremendously.

Just to be clear on grounding the generator. I should connect the generators ground to a negative post on any of my batteries?

Christopher,

Connect the generator ground to the same battery negative that is connected to your main engine. This is what your boat DC system considers as ground.

Kevin