Inverter location for the R21-EC

[Pearl]

On my 21EC I have an inverter installed in the pilot house. The length of the cable run is roughly 20', I am using 2 AWG cable. The low voltage alarm comes in quite often due to voltage drop, because of the length of run. If any other 21 owners have an inverter installed where did you mount it? Thank you

 

[happysoundman]

Hi , the best thing to do is to put the shortest input(12 volt) cable , it is better to run the lenght on 120 volt , you loose less power when the inverter is located close to the battery .
I Hope it Will help you a bit, also just curions to know what model of inverter ar you using , and is your coffee machine work well on it ?

 

[RProffer]

Did you install a new bank of batteries dedicated for the inverter? What size inverter do you have? If you are running the inverter off the house battery, then it will only support a small (300w?) inverter capable of charging a cell phone or laptop. If you have a 1000w to 1500w inverter, then it needs a third battery bank, preferably a set of 6v golf cart batteries connected in series. Standard 12v type 24 batteries cannot do the job. The factory says they install inverters on the R21 under the aft bench seat. I don't recommend that location. The inverter needs to be installed in a dry location and under the bench is too wet from rain, and condensation. I put my inverter under the helm seat. A large size cable needs to be run to the inverter depending upon your current draw and distance. I ran #1 AWG Gauge Battery Cable Tinned Copper Marine Wire. I got mine at http://www.genuinedealz.com/. They have good prices and will cut the cable to length, crimp on the connectors and provide shrink wrap insulators, with a fast turn around.

 

[Pearl]

I purchased the boat used and the inverter was already installed. The inverter is tied to the AC batteries, the inverter is a Cobra 1500 watts and is located above the refrigerator. I installed new 12v type 24 deep cycle batteries and changed the cable from #4 AWG to #2 AWG last year. It helped some, but still the low voltage alarm occurs when making coffee. Can I install 2 6v batteries in a series and still use the AC? Sounds like I also need to increase the wiring size again. Thank you

 

[RProffer]

I assume the batteries are installed under the aft bench on the port side, same as mine. Installing golf cart batteries will increase your output amperage significantly. I used the Interstate GC2-XHD-UT battery https://www.interstatebatteries.com...03,Nr~AND(P_unique_id:Trojan+T105+GC2-XHD-UT). It is slightly larger that the type 24 battery, which means the battery mount will need to be modified. Remove the batteries then remove the battery mount. Cut off the outboard piece of the mount. If you try to put the GC2 batteries in the mount you will see what I am talking about. With the rest of the mount and the hold down straps in place, the batteries will be secure.

 

[SGIDAVE]

I purchased the boat used and the inverter was already installed. The inverter is tied to the AC batteries, the inverter is a Cobra 1500 watts and is located above the refrigerator. I installed new 12v type 24 deep cycle batteries and changed the cable from #4 AWG to #2 AWG last year. It helped some, but still the low voltage alarm occurs when making coffee. Can I install 2 6v batteries in a series and still use the AC? Sounds like I also need to increase the wiring size again. Thank you

Hello Pearl,

Some basic calculations will help determine proper wire size.

1500Watts Inverter at 120 VAC results in 12.5 Amps current. BUT, that's 12.5A at 120VAC; the inverter makes that from 12VDC which will require 10X the amps (120/12 = 10); thus the wires connecting the batteries to the inverter will need to comfortably carry 120 AMPs. The next critical calc is dependent upon the LENGTH of the wires between the batteries and the inverter. You said 20 feet in your first post; does that include the length of BOTH (hot AND ground) conductors? That's important at 120Amps because you will go UP wire sizes between 25, 30, 40 feet.

Check bluesea.com. They have TONS of support info including a "Circuit Wizard" wherein you enter pertinent info then it calculates the appropriate wire sizes based upon the level of voltage drop you select as acceptable. For this application you should plan on 3% voltage drop (NOT 10%).

Anyway, I'd go with 2/0 wire. Bigger if more than 20' TOTAL run length.

So you can see why putting the batteries and inverter CLOSE together is a good thing. Carrying AC current is easy from a wire size standpoint but carrying HIGH AMPERAGE DC is much more costly from a wire-size standpoint.

One other thing. Those wires connecting the batteries to the inverter MUST be Fused. Place the fuse CLOSE to the batteries; do not rely on the "circuit protection" built into the inverter. When there is a malfunction or, God-forbid, a dead short, those wires will get HOT and cause a nasty fire which would be prevented by proper fuse protection.

Something like the Blue Sea MRBF which incorporates a fuze into the battery terminal connection. Very slick.

Fair Winds,

/david