DC to AC inverter

Dustin Brewer

Dustin Brewer

Member
Sep 14, 2020
52
Utah
Boat Info
1999 Sea Ray Sundancer 270
Engines
7.4 liter MPI, Bravo III
Howdy all! I have a 99 Sundancer 270DA, with 2 Trojan T-105 golf cart batteries in series. The boat does not have a generator. The boat, when I bought it had an old 1500 watt inverter in the transom storage locker you could plug the shore power cord into. Its never worked, and I haven't really thought about replacing it until now. Does anyone run a set up like this? Only things we would run would be a tiny TV with a DVD player, small coffee maker at 900 watts, charging phones, and occasionally a laptop/tablet. Modified sine? Pure sine? Appreciate your help in advance!
 
Dustin Brewer said:
Howdy all! I have a 99 Sundancer 270DA, with 2 Trojan T-105 golf cart batteries in series. The boat does not have a generator. The boat, when I bought it had an old 1500 watt inverter in the transom storage locker you could plug the shore power cord into. Its never worked, and I haven't really thought about replacing it until now. Does anyone run a set up like this? Only things we would run would be a tiny TV with a DVD player, small coffee maker at 900 watts, charging phones, and occasionally a laptop/tablet. Modified sine? Pure sine? Appreciate your help in advance!
Click to expand...
A 1500 watt inverter is limited. A new 3000 watt modified or pure sine (better on motors, chargers and sensitive electronics) is very useful. We have a 3500 watt unit that will run anything we need. We also have an automatic transfer switch that disables it when we plug into shore power. Inverters need good, deep cycle batteries and a high output alternator to keep them charged. Using it for electric stoves, frying pans, toasters, etc. will draw batteries down quickly. We use ours primarily for a small coffee maker, microwave and TV/DVD player. Occasionally for the blender. Inverters do draw some power in standby mode and they are about 90% efficient so we use a 12 volt USB adapter for phone and tablet charging and turn it off when we don't need it. Ensure that you run sufficiently heavy cables from the batteries to the inverter; they can draw a lot of current.
 
Are these the only batteries on board, including for starting? AC appliances tear through 12V batteries in a hurry.

For the coffee maker:
P = V x I
I = P / V = 900/12 = 75A
@90% eff'y: 75/0.9 = 83A

The pair of 6-volt T-105s give you a little over 100 minutes at that draw.

Might be a good idea to have a backup for starting...
 
bajturner said:
Are these the only batteries on board, including for starting? AC appliances tear through 12V batteries in a hurry.

For the coffee maker:
P = V x I
I = P / V = 900/12 = 75A
@90% eff'y: 75/0.9 = 83A

The pair of 6-volt T-105s give you a little over 100 minutes at that draw.

Might be a good idea to have a backup for starting...
Click to expand...
Definitely! I have a separate 12v deep cycle for the engine. Learned from others mistakes! Haha
 
Transom locker is a pretty wet/humid location. You don't want it in the bilge (explosion risk) but maybe there is a more protected location in a storage compartment? I installed mine in a cockpit storage location well in the back (right above the batteries too). In terms of size, mine is only 1800watts but is fine for what I use it for, which is not much.
IMG_1568.JPG
 
jmauld said:
Don't you want a starter battery for the engine?
Click to expand...
You are correct! Start batteries are designed for a large current output of short duration and minimal draw-down. Deep cycles are designed for lower current demands of longer duration and deeper draw-down.
 
I didn't even think about that! Good call, time to switch it out. Size/CCA for the 7.4?
 
FWIW - I have the factory setup with 2 deep cycle batteries for years without issues on my 1999 270 da. Don’t really see a need for three batteries.
 
Hey all so I am new to the site and just bought a 2004 Sundancer 240. My boat has a Microwave and a refrigerator we can only be used with Shore power which I have . Not to savvy when it comes to inverters ext. but it seems possibly l can install a inverter and while out on the water at least get my refrigerator working and use the microwave we need it but keep the Circuit breaker switch off on the microwave so it doesn’t drop power . Am I on the right track with this or not?
 
Leonard Schendel said:
Hey all so I am new to the site and just bought a 2004 Sundancer 240. My boat has a Microwave and a refrigerator we can only be used with Shore power which I have . Not to savvy when it comes to inverters ext. but it seems possibly l can install a inverter and while out on the water at least get my refrigerator working and use the microwave we need it but keep the Circuit breaker switch off on the microwave so it doesn’t drop power . Am I on the right track with this or not?
Click to expand...
If you have a marine fridge it also works on 12 volts and 120 shorepower.

We have a 3500 watt, pure sine inverter and an automatic transfer switch with 2, deep cycle house batteries. It powers the microwave without issue.
 
Juliery said:
If you have a marine fridge it also works on 12 volts and 120 shorepower.

We have a 3500 watt, pure sine inverter and an automatic transfer switch with 2, deep cycle house batteries. It powers the microwave without issue.
Click to expand...
Thanks you
What type of transfer switch do you use
 
Juliery said:
If you have a marine fridge it also works on 12 volts and 120 shorepower.

We have a 3500 watt, pure sine inverter and an automatic transfer switch with 2, deep cycle house batteries. It powers the microwave without issue.
Click to expand...

That brings up a good point. When the inverter is engaged, the fridge will sense 120VAC and switch over to that, which is not the most efficient mode. It might be worthwhile to turn off the AC breaker for the fridge when running the inverter.
 
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