Power Inverter Install help!

[Dirty Dawg]

Hello all, I am thinking of installing a power inverter on my 2000 21 ft Sea Ray bowrider with dual batteries. I figure it would be nice to run an appliance, blender, a small TV and add some versatility to my boat.

Location for install my be tricky in that it needs to be as close to the battery as possible but away from gasoline source due to explosion potential and dry. So that rules out putting it back by the transom. I have my steering console /storage are were the controls are that would be ideal. There is a fuse box there to tap into, but I am not sure if those wires are heavy enough to supply the amount of voltage required. They suggest 2-4 AWG( not sure what the boat is wired with, and no access to the boat until next week) due to voltage drop as you move away from the battery. Any thoughts on these gauges?
There is a small compartment next to the battery but not completely isolated from the motor and not very water proof so I don't think its a good place.

What size inverter should I consider?

Any thoughts or comments would be appreciated!! Ike

 

[joed]

Re: Power Inverter Install help!

The DC power wires need to supply 10 times the amps of the AC wires.
Example. If you want 5 amp AC then you need 50 amps DC. That is likely the reason for the close to battery requirement.

 

[Boatin Bob]

Re: Power Inverter Install help!

You will have to run heavy gauge wire to it no matter where you put it, the existing wiring on your boiat is no where near heavy enough. You need to calculate everything you might be running on it and how many of those at the same time to figure out how big you will need, you may even need another or bigger battery to run it and how were you going to charge the battery?

 

[Dirty Dawg]

Re: Power Inverter Install help!

Thanks for the replies. This may be more complicated then I thought. I do not plan to run anything continuously on it. Perhaps a blender for ten minutes, a air inflater to inflatables. run a cell phone down on power or maybe an MP3 payer. No long term heavy draining items. I was assuming that my alternator would recharge the batteries. The inverters have low volt alarms/shutoffs to approx. 10 volts, will that avoid draining the battery below a point that the boat would start? I also have dual batteries, so I could dedicate one specifically to it. Trying to keep it simple if possible, am I missunderstanding something?

Any suggestions on a company? Thanks Ike

 

[jlinder]

Re: Power Inverter Install help!

There are 2 concerns - wires overheating and voltage drop.
4 GA is good for around 80 amps, 2 ga is good for around 120 amps That is to prevent overheating.

For voltage drop you need to be concerned with amperage (12 volt side) and the length of the wire. Consider this - if you have a 1.2 volt drop you are losing 10% of your power in the wires. To make up for this your inverter needs to draw even more power making it worse.

Do a search for voltage drop on this forum. There are a lot of good articles and explanations and even links to some calculators that will tell you how big a wire you need for a certain amperage and wire length.

 

[ezeke]

Re: Power Inverter Install help!

You can use the voltage drop calculator at this site: http://genuinedealz.com/voltage-drop.html

 

[Moody Blue]

Re: Power Inverter Install help!

Basic thing to consider is power out of the inverter equals power in to the inverter. Can't get something for nothing.

If you are powering say a 10A 120Vac load from the inverter, then 1200 watts of power is being used. That means that the 12Vdc battery(s) must supply 100A to the inverter. That is alot of current, enough to arc weld two pieces of steel together. That is the reason you require large gauge low voltage cables. You will quickly run the battery down drawing that kind of current.

You mentioned loads that are typically low power, but you must design for the maximum potential of the inverter or you will create a fire hazard.

 

[Dirty Dawg]

Re: Power Inverter Install help!

Thanks all, I never realized what type of power we were discussing here. Sadly I simply thought that the plug of the appliance that am using is approx 12 gauge and thus the inverter would need the same. Simple, but not so. Will rethink this thru and see if I can stay close to the batteries. I want to say that the use would be a more emergency type of situation and an occasional blender.
My batteries are series 27 with 750 watts and a reserve of 160. Probably a dumb question but, what does that exactly mean? Can it produce 750 watts for 160 minutes? So if a appliance was draining 500 watts would it last for 240 minutes in the perfect world per battery? I know that the batteries age and the inverter and cables are inefficient in their energy transformation but in theory? Also if my motor is running and the alternator working properly, how much energy is it recharging the battery with.
Sorry but my last electrical physics lessons were in high school and that was a while ago and my mind well it aint what it used to be!!
Thanks Ike

 

[dan t.]

Re: Power Inverter Install help!

can you put a dedicated battery under the seat and put the inverter in the console? run #0 cable to the inverter?.thru a 75 or 100 amp switchable circuit breaker . blue seas makes these ,not cheap but safe and convient

 

[Dirty Dawg]

Re: Power Inverter Install help!

Dan the boats design will not allow it. Its a sun deck with to captains seats at the split console , a "bench' over the engine compartment /transom area and the open bow seating up front. The existing batteries sit at the transom area. Room for a battery back there but the others are there already. Up by the console there are two dry areas but did not want a battery up in those areas, also how would I recharge it from the engine? It actually not too difficult to run cables from the engine compartment under the ski locker up to the steering console compartment and place the inverter there. The rest of the electronics are there, but its about 10 feet away and the size of hate cable needed some what surprised me.
It is not something we would use often, but I like the versatility if needed.
I am just curious how much draining on my batteries would exit and how fast my alternator would recharge it on say a 500 watt item. I have Dual batteries, and always float with just one to allow the engine to start from the other if I have played to many songs and drained the one battery to far down. Thanks all Happy Thanksgiving Ike
Ike

 

[SKEETR]

Re: Power Inverter Install help!

Seems kindof overkill to run anything heavier than say 6-8awg on a 10' run. Most of the inverters in the 500w range come with relatively small 3' pigtails maybe 12awg. and often just have battery clips that attach to the posts.
I think if you fired up your motor, blended a few stiff drinks and shut 'er down you would notice very little loss from your battery. Inverters do drain energy when left on however so you will have to turn it off after use.

BTW like the picture, got a varmint like that of my own.

 

[Dirty Dawg]

Re: Power Inverter Install help!

Thanks for the info Skeetr and the compliment. That's the original Dirty Dawg that the boat is named after!! Ike

 

[pvanv]

Re: Power Inverter Install help!

For your intermittent needs, you might consider a setup like what we have on our sailboat. We installed a few high-quality 12v cigar lighter type outlets.

1- We use a GOOD 12v blender for the wife's dockside refreshments. The cheapies are just too wimpy. It plugs into a 20-amp cigar lighter socket (fed by 12-ga. wire on a fairly short run (less than 10 feet) from the battery bank. Works great.

2- For light-duty AC power, we use a "pocket inverter" of about 75-100 watts. It also plugs into a 20-amp cigar lighter socket. Plenty of AC for a cell phone charge, or a small CD/MP3 unit, etc. Also works great.

We can also use our 12v cooler (peltier-effect type, not very efficient, draws 4 amps DC) if we have the motor running (otherwise it would kill the battery after a couple of hours). But we don't do that very often, as it's supposed to be a sailboat, not a power boat.

The cigar lighter outlets need to be the GOOD variety. Not the cheap plastic ones. Ours are stainless, and come with a combo cigar lighter/map light cartridge. Also, the wiring needs to be done well. We had considered a built-in 400w or bigger inverter, but decided that we just don't need that much AC very often.

 

[jlinder]

Re: Power Inverter Install help!

My batteries are series 27 with 750 watts and a reserve of 160. Probably a dumb question but, what does that exactly mean? Can it produce 750 watts for 160 minutes?

I think you have things confused. Your battery probably is rated at 750 CCA, which is Cold Cranking Amps. This is how much amperage your battery can supply max when it is cold. Under normal conditions you may be able to get an extra 160 amps.

What you are looking for is amp-hour rating on the battery. This will tell you how long you can run the inverter. Unfortunatly this is a very hard number to get. Assume you are around 75 to 100 amp-hours on your battery.

If you are running a 100 watt bulb you are probably drawing about 9 amps. The formula is Watts = Volts x Amps then allow some loss for the inverter inefficiency. If you have a 90 amp hour battery a fully charged batter would be dead in 10 hours under ideal conditions (of course you don't want a dead battery.)

Hope that helps.

 

[Dirty Dawg]

Re: Power Inverter Install help!

Jlinder, Thanks for the info, just what I was looking for. I just wanted to understand the basic function and output of a battery.
Pvanv thanks for the advice , something similar is what we plan on doing, but may install the inverter just so it is there.
Thanks again Ike

 

[V8BoatBuilder]

Re: Power Inverter Install help!

My batteries are series 27 with 750 watts and a reserve of 160. Probably a dumb question but, what does that exactly mean? Can it produce 750 watts for 160 minutes?

The important number here (for the inverter, with the engine off) is 160.

"160" is your reserve capacity, which is in minutes at 20amps. When your batteries were brand new, they could power a load of 20 amps for 160 minutes, 2.5 hours before being "dead."

The average Group 27 deep cycle, wet cell battery will provide around 90Ah. Remember, batteries discharge faster with a higher load applied.

 

[SKEETR]

Re: Power Inverter Install help!

So if he was running a std household blender of 400w on an inverter he would be running 36A and could blend continuous drinks for 2.5 hrs on a 90Ah battery right? Man that is alot of drinks. Even at 2 hrs and 5min a pitcher that is 24 pitchers. Sounds like a party to me.

 

[V8BoatBuilder]

Re: Power Inverter Install help!

So if he was running a std household blender of 400w on an inverter he would be running 36A and could blend continuous drinks for 2.5 hrs on a 90Ah battery right? Man that is alot of drinks. Even at 2 hrs and 5min a pitcher that is 24 pitchers. Sounds like a party to me.

Pretty much, but inverters are only about 80% efficient. It doesn't change the calculations too much on this load.

400w load x 1.2 efficiency = 480w Usage / 12.25 volts = 39.2 Amp DC draw, so 90 amp-hours / 39 Amps = 2.3 hours of blend time.

If the engine was running however, and the alternator was outputting at least 39.2 Amps, then the usage would not be limited by the battery!

 

[SKEETR]

Re: Power Inverter Install help!

Boats and booze, "great math motivation."

 

[Dirty Dawg]

Re: Power Inverter Install help!

Hey what happened to my auto "subscribe to post"?
Thanks for the addtional info. Great to know, but may have to unplug the blender to play the Ipod, but that should not draw to much voltage.

The draw will most likely happen will the engine is running reducing the draw> Thanks again all Ike