Inverter Battery Useage Questions

[Juliet 15]

Greeting, all. I trust everyone is finding some way to get their boating fix in these days of COVID.

I was thinking of increasing my inverter size to accommodate more items. However, I could not determine the answer to a couple things. Anyone know the answers?

1. Does an inverter suck down battery power at a constant rate, regardless of the AC draw on that inverter? IOW, does a 2000w Magnum draw a constant number of amps, regardless of whether I'm actually using those 2000w?

2. If not, then if I'm running nothing off the inverter, but the inverter is on, what does it draw? I looked at several variations of Magnum inverters, and they listed various amperage draws, but the listed draw was not in line with inverter wattage. Example: a 4000w Magnum one claimed 25 amps (no explanation if that was max or constant draw), awhile a 2800w Magnum claimed 82 amps.

3. What is a "hybrid" inverter? There are 3000 and 4000w magnum inverters that look like they might be a drop-in replacement. Some are labeled "hybrid" inverters. No explanation as to what that means.

If a larger inverter uses more amps just by being connected (no AC items in use) I may rethink the project. Which would be sad because I'm running out of things to do on my boat after all this waiting...

 

[DDW]

1) inverters are about 90% efficient, so a 1000W draw from an AC appliance draws 1100 watts from the batteries. 1100/12V = 92A. The efficiency drops some at low draws, but that is a good rule of thumb.

2) The inverter current consumption is proportional to the equation above, except that at zero output they have what is called "idle current", the amount of current it takes to keep it on looking for a load to serve. This varies from small (<200 mA) in the best designs (Victron or Mastervolt for example) to 4 or 5 amps in the worst. Magnum is among the worst in this regard. Most of them have some power saving features which either drop the output voltage or stop all together and sample the line load to see if they should power up. I usually do not enable those as they cause more problems than the solve.

3) No idea what they mean.

With high idle current designs, you usually must turn the inverter off if you aren't using it, as the daily consumption can be quite high - if 4A then nearly 100AH/day. On the low idle current designs you can just leave them on all the time and plug in when you want power.

 

[Bacchus]

I think I have some partial answers for you. I have a Magnum inverter in our motorhome but not on our boat.
1 inverter DC amp draw will increase & decrease based on the AC loads you are powering
So shutting off hi power AC draws will save a large part of the A draw

2 you can significantly reduce draw as outlined above but if the inverter is left On it will use some reduced level of power "searching" for an AC load. I believe the lower the threshold you set the more power will be used but you can control that to some extent.
If you turn the inverter off there wi.ll be some parasitic draw but that will be very low 1/2 A or less I believe.

3 Hybrid is above my pay grade but I think these are dealing with multiple power sources. I believe these are often used where solar power & charging are part of the system. I dont have solar so that's about all I can offer. Others will likely have more info here as many have significant solar.

Just be aware that with Magnum inverters they always recommend disconnecting Pos batty leads first and attaching last to avoid potential damage to the inverter.

 

[Cigatoo]

My Master Volt 2500 watt inverter with 100 amp battery charger draws about 2 amps at idle.

 

[O C Diver]

Most inverters are more than 90% efficient in much of their range. There not at the extreme low and high end.

A hybrid inverter allows you to supplement power to a generator under full load. Let's say the generator is running at 75% capacity and an air conditioner compressor starts, exceeding the generators capacity. The inverter switches from charging the battery to inverting and supplements the generator's capacity to handle the air conditioning. When the air conditioner compressor switches off, the inverter reverts to battery charger, putting the energy it just used, back into the battery. That's how I understand it anyway.

I use an inverter on my boat 24/7. It has allowed me to use a far more efficient appartment refrigerator than the RV and marine refrigerators standard on most boats. After a night on the hook my bank has lost less energy with the refrigerator through the inverter than my old marine RV refrigerator.

Ted

 

[tiltrider1]

Most inverters are more than 90% efficient in much of their range. There not at the extreme low and high end.

A hybrid inverter allows you to supplement power to a generator under full load. Let's say the generator is running at 75% capacity and an air conditioner compressor starts, exceeding the generators capacity. The inverter switches from charging the battery to inverting and supplements the generator's capacity to handle the air conditioning. When the air conditioner compressor switches off, the inverter reverts to battery charger, putting the energy it just used, back into the battery. That's how I understand it anyway.

I use an inverter on my boat 24/7. It has allowed me to use a far more efficient appartment refrigerator than the RV and marine refrigerators standard on most boats. After a night on the hook my bank has lost less energy with the refrigerator through the inverter than my old marine RV refrigerator.

Ted

Hybrid will do the same with shore power. Let’s say you have a 30 amp shore power. You are using 30 amps and then some one plugs in a hair dryer. The hybrid will pull the extra amps from the battery.

 

[Juliet 15]

Thanks, everyone. That's helpful. A Magnum Drawing 2-4 amps at idle is a lot. That explains the considerable depletion I've experienced after 3 or 4 days on the hook.

And understanding the meaning of hybrid regarding inverters makes sense now. Great idea , tho maybe somewhat niche.

Last thought - does a 4000w inverter by nature draw significantly greater idle current than a 2000w inverter, or is it simply CAPABLE of drawing more?

 

[twistedtree]

Thanks, everyone. That's helpful. A Magnum Drawing 2-4 amps at idle is a lot. That explains the considerable depletion I've experienced after 3 or 4 days on the hook.

And understanding the meaning of hybrid regarding inverters makes sense now. Great idea , tho maybe somewhat niche.

Last thought - does a 4000w inverter by nature draw significantly greater idle current than a 2000w inverter, or is it simply CAPABLE of drawing more?

Just one caution.... the term "hybrid" for an inverter more commonly means that it can run off batteries or it can connect to incoming AC. This distinguishes them from inverters used in grid tied homes that only convert high voltage solar to grid power, and can't operate off batteries. I think Magnum stands alone using "hybrid" to describe what is more commonly called "power assist" or "load boost" or something like that. So just check carefully for whatever manufacturer you are considering to be sure you understand their terminology.


As for idle load, it may or may not be greater for larger inverters. The actual values can be found in the inverter spec sheets. Magnums appear the have an idle power consumption of about 25-30W across the board, so doesn't make much difference which size unit you get. The rest of the consumption is of course based on what you use at around a 90% conversion rate

 

[Cigatoo]

My Master Volt 2500 watt inverter with 100 amp battery charger draws about 2 amps at idle.

2.5 amps as measured today

 

[FF]

"I use an inverter on my boat 24/7. It has allowed me to use a far more efficient appartment refrigerator than the RV and marine refrigerators standard on most boats. After a night on the hook my bank has lost less energy with the refrigerator through the inverter than my old marine RV refrigerator. "

I have a hard time comprehending how this can be.

An sitting inverter eats 2 or 2.5 per hour amps just thinking which would be about 50 Amps per day .

A house hold fridge maximizes interior volume , so is frequently shy of insulation.

A quality DC fridge uses a computer to adjust the compressor speed to run as slow as possible , and maintain the interior temps.

Depending on brand and location most will eat 50-100AH per day .

Where do the savings (except initial cost) come from??

 

[High Wire]

The idle or standby current (listed as watts in the spec page) will be greater with a larger wattage inverter. It takes power to keep the electronic workings going even when not supplying any load. The bigger the inverter, the more stuff to keep awake. Magnum has a "Search mode" which sends out pulses (about 2 per second) to detect if any loads are turned on. By doing so the idle power drops from about 25 watts down to about 8-10. The search mode is an option that can be turned on or off from the remote control panel.
If you buy the Magnum, buy the remote control panel. There are so many more options available that are not available without the remote. Otherwise the inverter/charger is programmed for default values. For example, the shore power draw can be limited down to 5, 10, 15, 20, or 25 amps. Very useful for when you are plugged into a sketchy shore power outlet where the default value of 30 amps will trip the shore power every time.

 

[Art]

"I use an inverter on my boat 24/7. It has allowed me to use a far more efficient appartment refrigerator than the RV and marine refrigerators standard on most boats. After a night on the hook my bank has lost less energy with the refrigerator through the inverter than my old marine RV refrigerator. "

I have a hard time comprehending how this can be.

An sitting inverter eats 2 or 2.5 per hour amps just thinking which would be about 50 Amps per day .

A house hold fridge maximizes interior volume , so is frequently shy of insulation.

A quality DC fridge uses a computer to adjust the compressor speed to run as slow as possible , and maintain the interior temps.

Depending on brand and location most will eat 50-100AH per day .

Where do the savings (except initial cost) come from??

My question; regarding an inverter draining pre charged battery energy - as compared to amount of energy required to keep battery charged:

Seeing as inverter has some 10% efficiency loss during the drain of battery DC change to create AC input; and, it uses a bit of DC power while continuously "hunting" for the next AC requirement... doesn't that automatically mean there is considerable fossil fuel energy loss for keeping batts charged?

In other words... regarding reduced overall energy efficiency loss: Wouldn't it be more efficient to have a gen set's auto-on/off feature kick in when items such as a freezer's cooling,, washing machine or dryer's energy need becomes present? And, then, rather than having items such as TV's being AC wired... have DC wired TV's that can receive energy right off the batt bank, rather than through a 10% +/- energy wasting inverter/converter?

Of course that means the gen set may "want" to run at inopportune times while in some locations [such as being anchored in harbors near to other boats]. So, in situations such as that, the gen set auto-on/off feature would need to be shut off with inverter use turned on.

Therefore; it seems logical for making inverters truly efficient: That solar power is the energy source primarily used for keeping batts charged. With auto-on/off gen set aboard for supplying supplemental power to AC appliances and for batt-charging power during overcast days.

 

[Juliet 15]

The idle or standby current (listed as watts in the spec page) will be greater with a larger wattage inverter. It takes power to keep the electronic workings going even when not supplying any load. The bigger the inverter, the more stuff to keep awake. Magnum has a "Search mode" which sends out pulses (about 2 per second) to detect if any loads are turned on. By doing so the idle power drops from about 25 watts down to about 8-10. The search mode is an option that can be turned on or off from the remote control panel.
If you buy the Magnum, buy the remote control panel. There are so many more options available that are not available without the remote. Otherwise the inverter/charger is programmed for default values. For example, the shore power draw can be limited down to 5, 10, 15, 20, or 25 amps. Very useful for when you are plugged into a sketchy shore power outlet where the default value of 30 amps will trip the shore power every time.

Thanks, High Wire. I have the remote installed for my existing 2000w - I'm hoping it will suffice for a larger newer one. In fact I'm hoping for a drop in replacement. Magnum might not be the best, but it's worked. Has anyone tried using and older (2012-ish) remote pane with a newer inverter? I plan to call the company before doing it. You'll know when I do - there'll be a Magnum 2000w inverter for sale here. &#55357;&#56833;

Once I install a new inverter I have to run some wiring to add things to the inverted circuit. The PO has almost nothing in the inverter, which is a strategy I understand. I just feel differently. I have 2 large house banks (12v and 32v) each with their own inverter, and a "throw" switch preventing concurrent use of both.
I think having a few more items on there will be nice for the admiral.

 

[DDW]

The standby or idle power used by inverters is a pet peeve of mine. I'd rather leave the inverter on all the time so I don't have to reset the microwave clock, don't have to remember to switch it off when I'm done, etc. And though the efficiency at high power is 90%, the efficiency only to charge your cell phone is about 10%. The "hunt" mode that many of them have is at best a compromise - you don't have to find the switch but your clock will not stay set, at some load it may switch on and off continuously, small loads will not trigger it reliably.

In general, line frequency inverters like the Magnum or Freedom have higher idle power than high frequency, though not always. Small inverters have less idle power than large inverters. Pure inverters have lower idle power than inverter/chargers. This is one reason to consider separate units for these functions, and also not oversize your inverter. My Mastervolt 2500W inverter (separate charger) on the sailboat uses 250 mA max per the spec at full idle (a bit less in practice). It can be left on all the time. The Victron 2000W inverter/charger in my trawler uses 700 mA at idle which is more significant, however it has a power saving mode that reduces the voltage of the output to about 90V, and reduces input to 550 mA, and it keeps the clocks running. Higher than I'd like but no where near the Magnum.

Another strategy is to install a small (like 400W) inverter for charging phones or computers or radios, and turn on the big one only for high power loads.

I've already converted the things that I can to DC - laptop chargers, USB chargers, etc. The efficiency of this is only slightly better than the AC inverter when actually charging, but the idle current much lower.

 

[sunchaser]

Like many, we have a 120/12volt fridge. At night when at anchor w turn off all 120 loads and inverter off as well. Why? Because at idle the inverter draws about 3 amps with TV, microwave and other incipient loads raising that to about 6 to 7 amps.

With our Magnum controller and two BMKs power management is facilitated. However, if we boated in hot weather and ran AC well into evening via genset, then we'd have different appliances, bigger alternators and new think strategies.

Point being, where you boat, what vessel you have and your cruising style impacts your inverter, solar, power management and strategies.

 

[twistedtree]

I'm one who has decided that it's worth the extra power consumption to have 24x7 AC power for the convenience, and so I can freely used AC appliances where desired. It's a price I'm willing to pay.


But within that context, I still pay attention to wasted power. So idle power consumption was a big factor in my inverter selection. Not the only factor, but it weighed heavily. And I look for efficient AC appliances, seek and destroy phantom loads, etc.


Also, you need to walk away from the old notion that an AC fridge is wasteful and a DC fridge it not. My last boat has a sub-zero which makes most people cringe when they think of the power. And I'm sure at one point in history this was well founded., But that fridge consumed right around the 100Ah (@12V) that FF cited as the range (granted the upper range) for a DC fridge. And it had an ice maker, auto defrost, and probably more capacity than a typical DC fridge. Yes, you need to add in the inverter loss, but it's a much closer match/race than history and dock talk would lead you to believe.

 

[syjos]

I'm not sure I understand the concern about power consumption of an idle inverter.

The amount of power consumed by the idle inverter is replenished in less than 10 minutes of generator running.

And if the concern is the noise or vibration of the running generator, install a GenSep, better muffler, quieter sound shield or a new generator.

We run the generator 2 to 3 hours a day at anchor and sometimes forget it is running because it is so quiet.

 

[Juliet 15]

Syjos,


Good question. I could just run the genny. You're right. My underlying focus is that very few things are connected to my inverted AC leg. So I began looking at how to connect more thngs to it. Then I realized it might be too small. So I looked at bigger inverters. Which led me to wonder whether getting a bigger inverter (in and of itself) reduce my time running on the batteries. Now would I need to get a bigger battery bank...


And on it went. Hence my questions.

 

[Simi 60]

I'm one who has decided that it's worth the extra power consumption to have 24x7 AC power for the convenience, and so I can freely used AC appliances where desired. It's a price I'm willing to pay.


But within that context, I still pay attention to wasted power. So idle power consumption was a big factor in my inverter selection. Not the only factor, but it weighed heavily. And I look for efficient AC appliances, seek and destroy phantom loads, etc.


Also, you need to walk away from the old notion that an AC fridge is wasteful and a DC fridge it not. My last boat has a sub-zero which makes most people cringe when they think of the power. And I'm sure at one point in history this was well founded., But that fridge consumed right around the 100Ah (@12V) that FF cited as the range (granted the upper range) for a DC fridge. And it had an ice maker, auto defrost, and probably more capacity than a typical DC fridge. Yes, you need to add in the inverter loss, but it's a much closer match/race than history and dock talk would lead you to believe.

We have all 240v onboard apart from lights and pumps.

On 24/7 are a
550 litre/20cubic ft two door fridge freezer (Samsung)
100 litre/3.5cubic ft freezer (Kmart)
125 litre /4.5cubic ft fridge (Samsung)
All front opening all around 14 years old

Several 240v TV screens,monitors and other appliances are on standby

Running that is 8x 220ah agm batts linked up to give 880ah @ 24v
Powering a victron 5000va/120 inverter charger which has been running non stop for 4 years while living aboard on anchor.

Batteries have never been below 80%, usually around 83%

 

[DDW]

I'm not sure I understand the concern about power consumption of an idle inverter.

The amount of power consumed by the idle inverter is replenished in less than 10 minutes of generator running.

And if the concern is the noise or vibration of the running generator, install a GenSep, better muffler, quieter sound shield or a new generator.

We run the generator 2 to 3 hours a day at anchor and sometimes forget it is running because it is so quiet.

I don't like to run my genset for 10 minutes. Last summer (about 4 months and 2000 miles on the boat) I ran the genset for a total of about 2 hours. It is a Northern Lights in a sound enclosure, inside a sound insulated engine room with a water separating muffler. But for resale value I'd probably remove it for the storage space. With a well designed DC system, the genset is superfluous most of the time. If your inverter draws 4 amps idle as some do, you've got 100AH to replace - there's your 2 hours of genset run right there.

I've run into people who have forgotten their genset is running because they think it is quiet. But I can hear it. If you are in a noisy anchorage with 20 other boats then the noise might be lost in the general din. In a truly quiet anchorage almost any genset will be audible.

 

[JDCAVE]

Therefore; it seems logical for making inverters truly efficient...

“Logical” for me is to turn the inverter “off” unless you need it, or if running on engine, or the batteries are topped up whilst on solar. The parasitic load can be significant when on the hook.

Juliette: Why do you have an inverter bank that is separate from a house bank? Why not have one big house bank?

Jim

 

[Jimintheair3]

If you want the facts and nothing but the facts, contact Dan Rowe!
https://www.donrowe.com
He will give you the information you want and has great prices.

As for as projects go, I was on a boat recently that had a water use counter. Very helpful you could see how much water a shower used and how much was left. Not an expensive item to install, but very cool!
Jim

 

[catalinajack]

A generator is not anywhere close to superfluous most of the time if one boats in truly hot weather high humidity areas for any length of time. A generator in the South is a must for most boaters. Our DeFever 44 came with TWO generators, a 12.5kw (2,525 hours) and a 7.7 kw (3,750 hours). For most of its life before we bought her, this was a Southern boat (Florida, Louisiana) which explains the high generator hours. We have added maybe 100 hours to each, probably less. We live aboard in Maryland. Early in our ownership, I posed a question on this forum about perhaps removing one of the generators. The broad consensus was no. But, there are times when having that extra space would have been nice. For resale value, I would think removing the only on-board generator would be a negative in any market but that is just my opinion.

I don't like to run my genset for 10 minutes. Last summer (about 4 months and 2000 miles on the boat) I ran the genset for a total of about 2 hours. It is a Northern Lights in a sound enclosure, inside a sound insulated engine room with a water separating muffler. But for resale value I'd probably remove it for the storage space. With a well designed DC system, the genset is superfluous most of the time. If your inverter draws 4 amps idle as some do, you've got 100AH to replace - there's your 2 hours of genset run right there.

I've run into people who have forgotten their genset is running because they think it is quiet. But I can hear it. If you are in a noisy anchorage with 20 other boats then the noise might be lost in the general din. In a truly quiet anchorage almost any genset will be audible.

 

[HiDHo]

with Catalinajack.
When we bought our boat 12 years ago it had two 8D batteries and no generator or inverter. We had a NL 5kw generator installed along with two 16,000 btu heat pumps. We changed out the two 8d batteries for 4 golf cart type 6 vdc batteries. We also changed out the worn out Norcold for an apartment type 120 vac refrigerator freezer.
We run the generator almost 100% of the time when cruising. Only one time in 12 years has the generator been inoperable causing us to head into a marina for shore power.
I’m in the process of installing an inverter capable of running the refrigerator in case we had another inoperable generator incident.
Just an alternative to having a very expensive inverter charger setup that has seemed to work for us.

 

[OldDan1943]

I know a guy who put a large capacity inverter on board and claimed he never had to worry.
I said nothing.
Folks have to realize and accept, if you have a large capacity inverter, you better have the batteries to power that inverter and charger and/or solar panels to keep the batteries charged.
Some might say, “I run my gen a couple hours a day.”, well that sounds all well and good but, if your battery charger is small, it might take more than an hour or two to keep the batteries charged if anchored out.
There ain’t no such thing as a free lunch. The closest is solar panels assuming you do not figure in the cost of the panels and circuitry and life expectancy of the panels.
One nice thing about solar panels is, IMO, the replacement panels will, I hope, be more efficient.

 

[Juliet 15]

JDCave, good question. The boat came with 2 banks, one 32vdc and one 12vdc. It's an old Hat that hasn't been converted from the original 32v electrical system. The PO installed the 2nd 12v system I believe to increase time on the hook. I can use up one bank then the next bank if needed I guess.

 

[FF]

, “I run my gen a couple hours a day.”, well that sounds all well and good but, if your battery charger is small, it might take more than an hour or two to keep the batteries charged if anchored out."

With normal Lead Acid batts (LA) a few hours a day works , but since the batts are never at 100% the bat capacity is slowly lowered .

Some folks will oversize the house batts 20-40% to make up for this eventual loss.

Solar is a great help as it has the long charge time needed to get to 100%.

A night at the power pole once a week is also a help for folks without solar.

 

[DDW]

A generator is not anywhere close to superfluous most of the time if one boats in truly hot weather high humidity areas for any length of time. A generator in the South is a must for most boaters. Our DeFever 44 came with TWO generators, a 12.5kw (2,525 hours) and a 7.7 kw (3,750 hours). For most of its life before we bought her, this was a Southern boat (Florida, Louisiana) which explains the high generator hours. We have added maybe 100 hours to each, probably less. We live aboard in Maryland. Early in our ownership, I posed a question on this forum about perhaps removing one of the generators. The broad consensus was no. But, there are times when having that extra space would have been nice. For resale value, I would think removing the only on-board generator would be a negative in any market but that is just my opinion.

Yes, the exception requiring a genset is AC which takes a lot of power. And having bought my trawler in Tennessee during a heat wave, I completely agree that AC is necessary to sustain life in such a climate. That boat is now in the PNW, I've run the AC perhaps six hours in two years.

 

[Lepke]

My Magnum MS-PAE inverter is on 100% of the time. All AC passes thru. If shore power fails, it switches to battery and back to charging when power is restored. When the mains are running a dedicated alternator keeps the inverter banks up. If the banks get low, the inverter starts a generator. Hot water is made only on shore power or when a generator runs. The inverter has stopped my generator use by about 90%. I rarely use air conditioning and never when cruising because I avoid hot weather.

 

[O C Diver]

"I use an inverter on my boat 24/7. It has allowed me to use a far more efficient appartment refrigerator than the RV and marine refrigerators standard on most boats. After a night on the hook my bank has lost less energy with the refrigerator through the inverter than my old marine RV refrigerator. "

I have a hard time comprehending how this can be.

An sitting inverter eats 2 or 2.5 per hour amps just thinking which would be about 50 Amps per day .

A house hold fridge maximizes interior volume , so is frequently shy of insulation.

A quality DC fridge uses a computer to adjust the compressor speed to run as slow as possible , and maintain the interior temps.

Depending on brand and location most will eat 50-100AH per day .

Where do the savings (except initial cost) come from??

Sorry I missed this when it was originally posted.

As you must have forgotten from my refrigerator install thread, I bought the most energy efficient apartment refrigerator for model year 2017. It consumes .8 KW of electricity per day. Unlike RV refrigerators masquerading as marine units, apartment refrigerator have to submit to government standardized testing for real power consumption. So I knew my new refrigerator was very efficient. While RV units may have efficient variable speed compressors, they often have crap for insulation and aren't required to post their energy consumption numbers for everyone to see.

To answer your question on savings:

I replaced a 7 cuft. Norcold refrigerator with a 10 cuft. FROST FREE Summit refrigerator. It is 50% larger, FROST FREE, and uses half the energy. While the unit I replaced had an older style compressor, their new unit still has the same garage insulation. It doesn't matter how efficient the compressor is if it rarely shuts off because of crappy insulation.

A 12 hour night on the hook without microwave use, rarely pulls my 900 AH battery bank down to 90%. Maybe someone should ask the RV refrigerator manufacturers why they don't post energy consumption numbers.

Ted