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Old 10-14-2017, 05:28 PM   #1
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I Need an Education on Inverters, Please

First off, thank you all for the mountains of information you have provided to us in the past. I almost feel like I am earning my PHD in MH Sciences. But, here's a new one that we have an extreme interest in. Maybe others can benefit from your answers as well.

Some background: DW and I are actively researching our next MH purchase. Several of the candidates we are exploring have inverters installed. Inverters seem to come in many sizes, shapes, options and capacities. We can skip on all that for now, I just need a basic understanding of what I should and shouldn't be on the lookout for, and what my expectations should be.

I know that inverters consume 12VDC (battery) power and provide 120VAC power to various appliances, accessories, heaters and anything else that uses household electric power in the MH. I know that the inverter input is attached to the batteries and the output is connected to the appliances, and so forth.

Here are some questions I have due to my lack of understanding of the specifics. These are all based on a rig we are looking at with a 2,000W inverter and 2 X 6V batteries installed.

1) Watts an appliance consumes are all expressed in Watts per hour, right? If a microwave is a "1300W" device, that means if it ran for an hour, it would use 1300W (108A at 12V). So, if I wanted to run a microwave for an hour, I would need enough batteries to produce 108A, and still leave something in reserve so as to not damage the batteries. Did I get that right?

2) I will need to replenish the batteries at some point. I can charge them using a generator, solar panels, or line current from the pedestal. Can I use power from the inverter to run appliances while recharging the batteries? Do I have to disconnect the inverter to use other AC accessories from an alternative AC source? Is there some circuitry in the inverter that detects the source of power before passing it on the the 120V house circuits?

3) Is there a practical limit to the number of batteries I can connect the inverter to? For instance, I currently have 2 X 6V golf cart batteries. In the replacement rig, I'd like to have a minimum of 4, but would 6 or even 8 be better? Are there hazards to that many batteries?

4) IF we had a 2000W inverter, and 4 X 6V golf cart batteries and used 12v lights, TV, DVD player, coffee maker, etc sparingly (as when we would be boondocking) how long will our battery power last, based on YOUR experience?

We are getting excited about our next purchase and your input will be valuable to us in helping us make the right decisions. Thanks!
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Old 10-14-2017, 06:01 PM   #2
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I am interested in the position and as well. I will say that the most we have been able to run on our inverter has been a coffee maker. I am learning a great deal from this forum.
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Old 10-14-2017, 06:40 PM   #3
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You are on the right track. A watt includes the time division so if you want the amount of energy used in an hour, it would be watt-hour. Let’s not not go there as as long as you understand v x a = Watts, you have it.
Yes, you can join many batteries together to make more of a battery bank, but MAKE SURE you hook them up correctly. If yours are now 6v batteries, they are in series, but additional 6v batteries would be hooked in parallel to the two you already have. Find someone who absolutely knows how to do this if you attempt it. You can cause expensive damage or even an explosion if you do it wrong.
All the batteries should be the same age as older batteries might draw newer batteries down if they are put in parallel. The number in your battery bank can be big, but without knowing what you need to power, it is hard to guess. Big class As usually have about 400 amp-hrs as a minimum (that would be four 6v batteries wired correctly)
I would guess if you have a 2000W inverter, it is also a charger. If it is a modern 3 stage charger, it is all automatic.
Your RV is already set up that you are using 12v while you are plugged in and charging. Most of your lights and other things are 12v.
Boondocking is a balancing act of using your batteries, charging with a generator or from the pedestal, solar when needed. Watch your battery voltage carefully. If the voltage goes below 12.0v, you're below 50% of battery left and will hurt their longevity.
Hope this helps.
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Old 10-14-2017, 07:11 PM   #4
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Quote:
Originally Posted by Lindan n Jim View Post
First off, thank you all for the mountains of information you have provided to us in the past. I almost feel like I am earning my PHD in MH Sciences. But, here's a new one that we have an extreme interest in. Maybe others can benefit from your answers as well.

Some background: DW and I are actively researching our next MH purchase. Several of the candidates we are exploring have inverters installed. Inverters seem to come in many sizes, shapes, options and capacities. We can skip on all that for now, I just need a basic understanding of what I should and shouldn't be on the lookout for, and what my expectations should be.

I know that inverters consume 12VDC (battery) power and provide 120VAC power to various appliances, accessories, heaters and anything else that uses household electric power in the MH. I know that the inverter input is attached to the batteries and the output is connected to the appliances, and so forth.

Here are some questions I have due to my lack of understanding of the specifics. These are all based on a rig we are looking at with a 2,000W inverter and 2 X 6V batteries installed.

1) Watts an appliance consumes are all expressed in Watts per hour, right? NO. If a microwave is a "1300W" device, that means if it ran for an hour, it would use 1300W (108A at 12V). So, if I wanted to run a microwave for an hour, I would need enough batteries to produce 108A, and still leave something in reserve so as to not damage the batteries. Did I get that right? NO

2) I will need to replenish the batteries at some point. I can charge them using a generator, solar panels, or line current from the pedestal. Can I use power from the inverter to run appliances while recharging the batteries? Yes, but if the inverter has an automatic transfer switch this is not necessary when the generator is running or you are connected to shore power. Do I have to disconnect the inverter to use other AC accessories from an alternative AC source? Is there some circuitry in the inverter that detects the source of power before passing it on the the 120V house circuits? This is true in inverters that have automatic switches.

3) Is there a practical limit to the number of batteries I can connect the inverter to? For instance, I currently have 2 X 6V golf cart batteries. In the replacement rig, I'd like to have a minimum of 4, but would 6 or even 8 be better? Are there hazards to that many batteries? If you have space for them can carry the weight and have them properly connected you are good.

4) IF we had a 2000W inverter, and 4 X 6V golf cart batteries and used 12v lights, TV, DVD player, coffee maker, etc sparingly (as when we would be boondocking) how long will our battery power last, based on YOUR experience? You will have other loads that make this an unsolvable problem.

We are getting excited about our next purchase and your input will be valuable to us in helping us make the right decisions. Thanks!


Your units are out of wack.

A watt is a measure of Power, not energy: Power is the speed of use of energy.

Amps are a measure of current flow. Current flow by itself gives you no information on power or energy.

As you know, a watt is 1 volt times 1 amp so if you have a 12 volt system running 10 amps you are consuming 120 watts. If you run this 120 watts for 1 hour you have consumed 120 watt-hours of energy.

Battery energy storage is often expressed in amp-hours, but realize that it is not a true expression of energy unless you also know the voltage. A 6 volt battery with 220 amp-hours does not store the same amount of energy as a 12 volt battery with 220 amp-hours.
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Old 10-14-2017, 07:11 PM   #5
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Here are two Web pages to which I refer on these matters. I list Part 2 first, as it deals with inverters, but Part 1 is worth reading, too.

The 12volt Side of Life Part 2
The 12volt Side of Life (Part 1)

If you want your expensive batteries to live a long life, you need a battery monitor and to know how to use it. They act as a "fuel gauge" for your batteries. With an inverter, you'll be pumping a lot of juice out of and into the batteries. Common battery monitors are the Magnum ME-BMK (popular with coaches that have Magnum inverters installed) and the Trimetric TM-2030; there are other manufacturers and models.
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Old 10-15-2017, 06:28 AM   #6
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1) Watts an appliance consumes are all expressed in Watts per hour, right? If a microwave is a "1300W" device, that means if it ran for an hour, it would use 1300W (108A at 12V). So, if I wanted to run a microwave for an hour, I would need enough batteries to produce 108A, and still leave something in reserve so as to not damage the batteries. Did I get that right?

=> You would have consumed 108 amp-hrs, and your batteries would be dead. Your two 6 volt batteries will have a capacity about 220 amp-hrs in brand new condition, and you can use about half of that before they are dead.

-----------------------------------------------

2) I will need to replenish the batteries at some point. I can charge them using a generator, solar panels, or line current from the pedestal. Can I use power from the inverter to run appliances while recharging the batteries? Do I have to disconnect the inverter to use other AC accessories from an alternative AC source? Is there some circuitry in the inverter that detects the source of power before passing it on the the 120V house circuits?

=> First, the house batteries are also charged up the engine alternator when travelling. The engine alternator charges the chassis battery, and there is a device called a charge solenoid (or a similar function name), which connects the two battery banks together, thereby recharging your house batteries.
=> While driving down the road, wife has crockpot cooking dinner. Crockpot is 120vac, getting power from the inverter (inverters take 12v and make 120vac). At the same time, the engine alternator is charging the batteries back up.

=> Secondly, you need to understand that not all so-called inverters, are the same. Inexpensive inverters are just that, an inverter providing one function which is 12vdc to 120vac. Better 'inverters' (I'll just use an inverter from the Magnum line MS2000, there are other brands as well) actually perform three functions. They are an inverter, they are also a charger/converter (takes 120vac and makes 12vdc), and they have an internal transfer switch. The charger function charges the 12v batteries back up, so when on shorepower or generator and your coach has 120vac input, it will recharge your batteries. The transfer switch works this way, with your microwave plugged into the output of the transfer switch. If you don't have shorepower, then your inverter makes 120vac and passes it to the transfer switch, which then powers your microwave. If you do have shorepower, then the transfer switch senses that and passes the shorepower thru to the microwave circuit.
So when you have incoming shorepower the Magnum is doing two things: it is recharging the house battery bank, and it is passing the shorepower thru to whatever is connected to it. The microwave is NOT getting it's power from the 'inverter' section of the Magnum. (That would be inefficient, taking 120vac and converting to 12vdc charging battery, then taking 12vdc to invert and make 120vac).

---------------------------------------------------------

3) Is there a practical limit to the number of batteries I can connect the inverter to? For instance, I currently have 2 X 6V golf cart batteries. In the replacement rig, I'd like to have a minimum of 4, but would 6 or even 8 be better? Are there hazards to that many batteries?

=> The practical limit is weight and space (lead acid batteries need vented cargo space), and money. My coach came with 4 x 6v house batteries, and I added two extra, to have 6 x 6v.

------------------------------------------------------------------

4) IF we had a 2000W inverter, and 4 X 6V golf cart batteries and used 12v lights, TV, DVD player, coffee maker, etc sparingly (as when we would be boondocking) how long will our battery power last, based on YOUR experience.

=> The only high current device you have listed is the coffee maker, so a couple days. We have a residential refrig, mwave, TV's, satellite, and can run about a day. The big draw is the refrigerator. If we are driving thru somewhere and stop for the evening, we have no problem lasting thru the night, getting up, and driving the next day so the batteries are now recharged again.

=> You should note, that not everything in the coach can be run off an inverter. High current devices like A/C's, washer/dryer, fireplace, electric hotwater heater, etc circuits are not even connected to the inverter. They only work when connected to shorepower or generator. My coach has 4 circuits (Convection Mwave, Refrig, all the TV/Sat/DVD entertainment gear, and 'most' of the electrical outlets in the coach). However, my maximum current use (at the same time) is limited to 2000 watts. So if daughter is using 1500 watt hair dryer, better not turn on the mwave or will flip a breaker.

If you want to learn more, I have some charts I can send which explain how all the functionality and circuits work together. Just message me your email address (and put in subject line charts) and I'll be happy to send them (PDF and PNG files). Here's a snipit from one of them, showing how the 4 circuits (bottom right) get their shorepower from the Magnum xfer switch passthru. The second one shows how the 4 circuits get their power from the house batteries/inverter functionality of the Magnum.

(also note: all coaches can be different. This is how MY coach works, but it is pretty generic functionality and if you can understand this, then it will go a long way to helping you figure out exactly how your coach is similar or slightly different)
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Old 10-15-2017, 07:06 AM   #7
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Originally Posted by Kiawah View Post
1)

=> You would have consumed 108 amp-hrs, and your batteries would be dead. Your two 6 volt batteries will have a capacity about 220 amp-hrs in brand new condition, and you can use about half of that before they are dead.

=> )
If you consumed 108 AH, the batteries would be discharged to about 50% capacity, they would not be DEAD.

If you consumed 220 AH, they would be discharged 100%. They still wouldn't be DEAD, just discharged.

In either case you would just recharge them.

Discharging to 50% capacity or less give the longest life of the batteries. Of course you can discharge them deeper but the amount of times you can discharge ( cycle ) them before they are dead is less.

Most deep cycle batteries have 1000 cycles at 50% discharge and 500 cycles at 80% discharge. Going to 100% discharge is not recomended.

If you don't have the room for more batteries, you can discharge them deeper then 50%. You will just get a shorter life from them.
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Old 10-15-2017, 07:14 AM   #8
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You're correct, should have chosen descriptive words more carefully.
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Old 10-17-2017, 03:05 AM   #9
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Monitor

The most important thing when using a inverter is a battery gauge of some sort showing how much you are draining and if you want your batteries last a long time do not go below 50% and your batteries will do fine .
I don't have a inverter or solar on my MH and don't do much boondocking.
I do have inverter/charger on my boat with 4-6 volt batteries and 2 -195 watt solar and been using this system since 2010 with 2 battery monitors and never go below 12 volts.
But when during day with great sun and panels working real good we use microwave and charge our 2 smart phones 2 tablets off inverter.
I use the inverter but watch my battery gauge making sure I don't go below 12 volts on my gauge and use TV and ant booster at night off inverter and if need to at night I will run my Gen and I run 3 ref 24/7 mostly from my 2-195 watt solar.
We anchor out a lot and some times be out for 3 weeks with no shore power,
wes just watch your battery state of charge.
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Old 10-17-2017, 12:32 PM   #10
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Now, you can also have or add a Ags, automatic generator start, if your running on inverter and the batteries get low you can automatically start genny to charge up,
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Old 10-17-2017, 01:21 PM   #11
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The most important thing when using a inverter is a battery gauge of some sort showing how much you are draining....
X2

and this
https://handybobsolar.wordpress.com/

you can close this thread now..... lol
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