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Old 07-02-2014, 17:55   #1
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solar newbie inverter question on draw

I'm getting my solar/wind systems back on line after lightning damage. It's all up and running, thanks largely to advice I got on this forum.

I've got a new battery monitor and shunt yet to install, along with a big fuse between the bank and the boat, etc. etc. yada yada. Just found out the lightning fried the controller on the CU-200 fridge too. I'm really getting a lot of hands on troubleshooting experience here. Oh boy.

I have a question about the inverters. How using them affects the battery.

The boat has two inverters. A nominal 4000 watt and a 750 watt. I know the 4000 watt is really only good for something like half that.

But my question is does an inverter put a constant load on the battery bank, or does that load fluctuate with the inverter's output?

in other words, does plugging in an ac appliance cause an increase in battery drain? Or do inverters pull their steady maximum as long as they're switched on regardless of their output load?
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Old 07-02-2014, 18:04   #2
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It fluctuates as the load changes. I watch mine do it with my Link 20 system monitoring the amp flow into-out of my battery bank attached my inverter and solar array. As my computers spin up or are crunching code while powered by the inverter, there is a higher amp draw on the battery bank than when they sit idle.
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Old 07-02-2014, 19:33   #3
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Re: solar newbie inverter question on draw

Inverters usually have a very small fixed DC current draw (overhead) plus a draw that is proportional to the AC current produced. In round numbers it takes 10 amps of 12 V DC to produce 1 amp of 120V AC.

So a toaster or coffee maker that draws about 10 amps AC should draw 100 amps DC from the inverter while on.

David
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Old 07-02-2014, 19:43   #4
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+1 to Davids reply. I used that same formula to size the solar panel and battery array for my worst case draw and the system has worked like a dream for the past year. From May thru Oct it produces enough power to run the designed load and more. During Nov - April it can pull the designed load.
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Old 07-02-2014, 21:19   #5
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Re: solar newbie inverter question on draw

if they pulled constant full power. every boat with an inverter would have dead batteries in about 2 hours.

they draw normally around 3 amps in standby

some have a sleep mode (like magnum) that will search for things pluged in. and turn on. still use a bit of power in sleep but not as much as standby. maybe like an amp? best to turn the inverter off when not being used to save all power.

when you use something off the inverter. they will use whatever power that device takes for the time it is being used.
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Old 08-02-2014, 06:45   #6
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Re: solar newbie inverter question on draw

Thanks for the info, that was exactly what I was looking for. Makes sense. Since I have to repair this system anyway, I'm trying to look at each component and plan ahead for possible future options. I bought a bigger MPPT than I need, for example. I put a cheap PWM on the panels likely to be replaced or changed first. I'm planning a new hard top and if I can fit that in with a nice flexible array I can stand on I want to junk all the glass.

I've been looking at what we're typically plugging in to the ac, and find that a lot of it is ac to dc converters to power computers, charge portable batteries in hand helds, phones, etc. Does anyone know of a good marine variable output dc to dc converter that would let me dial in whatever output and polarity I wanted direct from the boat's 12 volt supply?

Then all I'd need to charge things and run the tablets would be the right connectors. No inverter required. Am I correct in that this would be much more efficient?
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Old 08-02-2014, 09:09   #7
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Re: solar newbie inverter question on draw

Canibul:

Your approach of using a DC to DC converter will work, but I doubt that it will be that much more efficient.

A couple of years ago I bought a cheap Chinese converter and it let me adjust the output voltage from 15 to 20 or so volts. Since most laptops need 18-19 volts DC that worked fine. But it wasn't any more efficient than powering the laptop through a small 150 watt cigarette lighter inverter which has little overhead. The DC amps were essentially the same either way.

David
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Old 08-02-2014, 09:33   #8
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Quote:
Originally Posted by Canibul
Thanks for the info, that was exactly what I was looking for. Makes sense. Since I have to repair this system anyway, I'm trying to look at each component and plan ahead for possible future options. I bought a bigger MPPT than I need, for example. I put a cheap PWM on the panels likely to be replaced or changed first. I'm planning a new hard top and if I can fit that in with a nice flexible array I can stand on I want to junk all the glass.

I've been looking at what we're typically plugging in to the ac, and find that a lot of it is ac to dc converters to power computers, charge portable batteries in hand helds, phones, etc. Does anyone know of a good marine variable output dc to dc converter that would let me dial in whatever output and polarity I wanted direct from the boat's 12 volt supply?

Then all I'd need to charge things and run the tablets would be the right connectors. No inverter required. Am I correct in that this would be much more efficient?
Canibul, the easiest way to deal with DC-DC charging of small electronic devices is to buy cigarette lighter chargers for all of them, and install several cigarette lighter sockets. Done.

A large proportion of modern devices use 5v through a USB outlet - Blue Seas and others make fixed installed USB type outlets for this purpose. One could theoretically buy a 5v power supply and wire up the boat with USB outlets in every cabin. But that would be gilding the lily a bit, wouldn't it?

But I don't bother - I have a fantastic high power dual outlet USB charger which fits inside a cigarette lighter outlet and will charge two such devices simultaneously.

And when I am cruising with a lot of people on board, its hopeless to figure out hownto efficiently charge the myriad devices on board - I just leave the inverter on 24/7 and let people use their regular chargers.
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Old 08-02-2014, 09:35   #9
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Quote:
Originally Posted by djmarchand
Canibul:

Your approach of using a DC to DC converter will work, but I doubt that it will be that much more efficient.

A couple of years ago I bought a cheap Chinese converter and it let me adjust the output voltage from 15 to 20 or so volts. Since most laptops need 18-19 volts DC that worked fine. But it wasn't any more efficient than powering the laptop through a small 150 watt cigarette lighter inverter which has little overhead. The DC amps were essentially the same either way.

David
P.S. My laptop doubles as the ship computer and is used a lot. I found a 24v (!) power supply for it, cut off the cigarette plug, and hardwired it in behind the nav table, leaving just the DC cord sticking out. Works a treat!
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Old 08-02-2014, 10:19   #10
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Re: solar newbie inverter question on draw

They also sell 110v wall outlets now that have a 5v power supply built in and 2 USB sockets in addition to the 2 110v sockets. It's the same form factor as a regular wall outlet.
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Old 08-02-2014, 10:34   #11
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Re: solar newbie inverter question on draw

I leave my inverter off except when I need AC for something. I found that even in standby it uses almost as much power as my refrigeration system
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Old 08-02-2014, 12:28   #12
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I leave my inverter off except when I need AC for something. I found that even in standby it uses almost as much power as my refrigeration system
Ooh, I have done a lot of slagging off of Victron gear, with which I've had a heap of problems, but this isn't one of them. Victron inverters have "search mode", where they use mere milliamps "searching" when there are no AC loads, so you can leave them on with no worries.
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Old 08-02-2014, 13:53   #13
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Re: solar newbie inverter question on draw

Quote:
Originally Posted by Dockhead View Post
Ooh, I have done a lot of slagging off of Victron gear, with which I've had a heap of problems, but this isn't one of them. Victron inverters have "search mode", where they use mere milliamps "searching" when there are no AC loads, so you can leave them on with no worries.
It would be a consideration if I need to replace my current one someday. But currently it isn't a big deal to turn it off and on when needed, which I can do with my big toe on the remote panel.
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Old 08-02-2014, 15:38   #14
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Re: solar newbie inverter question on draw

I have to open a hatch reach in and flip a switch to turn either inverter off or on. The little 750 watt one is wired to one outlet in the boat, a standard dual ac house current style. I believe this is where previous owner charged his phones, etc. without using the 4kw.

We no longer have cigar lighter style outlets. I took them all out. I replaced them with a different connector with two heavy copper pins and a splash cap. I can't for the life of me understand why manufacturers chose to standardize on a socket designed in the 1940's for automobile cigar lighters. Too many moving parts, too much depth required, they collect dirt, etc. I bought enough of these new connectors to replace every cigar lighter on board, with a dozen spares. I cut the plugs off all the appliances, lights, etc. that had cigar lighters and put these two pin connectors on. They work great. No springy bits or cheap chrome contacts. Solid copper contacts. IN a pinch, I could strip two wires and just stick them into the female bulkhead connectors and they would work. I did make up a couple of adapters so that I could use a cigar lighter adapter with my new connectors if needed.

Thanks for the info on the inverters. It's all starting to fall in place now. I use the 750 watt for most day to day stuff, and have the 4kw in case I need to run a drill or something. Turn them off when not in use.
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