generator question

[ripped_78]

I have a 1995 Chris Craft 26' "cruiser" with a 7.4l Volvo. It has a dual battery setup and a 20 amp battery charger. I am wanting to keep a portable generator to hook up to the shore pwer cord when I am out, but I do not know which generator I should buy. I was told if i was going to hook this up to my shore power cord that i would want to have a generator with an clean energy inverter built in. Everything runs off the battery so the only thing the generator would be running is the battery charger. I would appreciate any opinions on this generator or what to do.
"http://www.walmart.com/catalog/product.do?product_id=6371182"

 

[Don S]

Re: generator question

Moving to Electrics & Electronics forum.

 

[tashasdaddy]

Re: generator question

when you say everything is running of the battery, exactly what is everything. doesn't you alternator charge your batteries. are you talking of using this at anchor?

 

[ripped_78]

Re: generator question

when I say everything I mean stereo, lights, tv, refridgerator,. When I am at anchor I would like to be able to runn all of these things without having to worry about draining the battery or having to run the motor. The onboard battery charger runs everything when it is hooked up to power so my goal is to hook up the charger to the generator. Do I need the "clean energy" generator or will a regular one be alright and is 1500 Watts enough for a 20amp charger?

 

[tashasdaddy]

Re: generator question

you need to know the draw of your charger. also placement of the generator, may drown out the stereo. i believe honda makes the quietest generator.

 

[Silvertip]

Re: generator question

A 1500 watt rating on a generator refers to its output at 117 Volts AC. That amounts to roughly 13 amps. A 20 amp on-board charger refers to 20 amps output at 12 Volts DC or 240 Watts. So your charger is limited to an accessory load of 240 Watts. If you add up the accessories you are running on 12 volts you might exceed the 240 W output of the charger which then becomes the restriction in the system. At 240 Watts output, the 117 Volt input to that charger would need to be something more than 240 watts due to the losses in the power conversion. So in your case anything larger than a 500 Watt Honda (or similar) generator would be a waste of energy since the charger it is feeding cannot deliver more than 240 Watts (20 amps). And what you really need to understand is that if your accessories are drawing more than 240 watts total, the excess is coming out of the batteries so the entire system is losing ground and you may still run down the battery. Until you do a load analysis you may be spending money on the wrong solution. That 20 amp charger is just that -- its a battery charger intended to keep batteries topped off. It is not a replacement for a true shore power system. If it turns out the loading is under 20A at 12V the system will work with a small generator. If its more than 20A a 1500W generator is no better than a 500W generator.

 

[wire2]

Re: generator question

Running audio equipment supplied by a standard battery charger will typically result in a horrible 120 cycle hum over the speakers. That's because the output of a charger is full wave rectified AC.
While you can filter the output with a choke coil and a large capacitor, the better way is a switching power supply. They're rated in watts, not amps, and nominal 15v units are usually adjustable between 11 to 16 volts. A 500 watt unit is only ~ 6" x 6" x 4", 3-4 lbs,(no transformer) and the output is super-clean. LH Research is a very respected name, pricey new but used ones available. Look for 115 v in, 15 v dc out. 500 watts will give 33 amps at 100% duty cycle.

 

[Chris1956]

Re: generator question

Ripped, Here is another way to analyze your power needs. Your boat has low power devices (stereo, navigation instruments, VHF) and high power devices (fridge, hot water heater, elec stove, microwave, navigation lights). If you are using the low power devices, you do not need to use the generator. However, you will want to put an isolator between the batteries and choose one battery (deep cycle is best) to supply all the "house" load. the other battery is reserved for starting the motor.

when you are using the high power devices, you will want to crank up the generator. Now, to Silvertips comment about the amperage of the battery charger. A lot of boats are intended to run some of their high power devices off 110VAC, supplied by the shore power cord. the battery charger is not sufficient (by design) to run the elec stove, microwave and water heater. Your generator must have enough capacity to operate these devices.

In addition, if it were me, I would buy a genny powerful enough to run high wattage fishing or party lights for the cockpit.