some more inverter and battery questions

[Oregonconversion]

Do I have to have a shunt on my batteries for my xantrex RV3000 to read them properly?
right now I just have 2 12V 225AH batteries in parallel.

I am using a coleman powermate 1850 (one 15 amp circuit) right now to charge m batteries, but it looks like Im only getting about 7 amps on the bulk charge. I know I im supposed to get lots more.... whats the deal?

When I do get a better generator, how many watts do I need to take full advantage of my battery charging?



Also, can I put my generator, batteries, and black water tank in the same bay?

[Oregonconversion]

really? noone? 

[bevans6]

OK, I'll take a shot at this.  I hate it when my questions get ignored too.  I don't know much about your specific inverter, so I'll look at this generically.  The inverter will sense the amount of charge the batteries need and supply charge appropriately.  If they don't need charge, they won't get much current.  Try drawing the batteries down to 50% or lower charge, which will be at about 12.1 volts with the inverter disconnected (load the batteries, draw them down, but get an accurate reading of charge level with the load disconnected).  Then re-connect the inverter (which is the charger as well, I presume), connect the AC to a known good supply (a pedestal, your house AC at home) and see what the charge level is.  It should trigger a healthy charge.  Take a reading, disconnect from the AC supply and connect to the generator.  It should let the inverter charge the batteries at the same rate as with the "house" AC supply.  A healthy 45 amp 12 volt charge is about 550 - 600 watts (after losses) which your generator should easily handle.

Drawing two 225 amp-hour batteries to 50% charge will take, you guessed it, 225 amp hours of use.  You have to figure out how to draw that much current out of them.  It would take me about a week of camping, but I don't have an inverter to draw big currents.  Just turn stuff on, be reasonable, and monitor your battery voltage.  Try not to take them below 12.0 volts for this test.

If you know how many amps your inverter can charge at, you can calculate the 120 volt AC current needed to let it do that.  The easy way to get a close estimate is divide the 12 volt charge amps by 10 to get 120 volt AC amps.  50 amp charge is 5 amps at 120 volts, near enough.  Multiply volts times amps to get watts. 5 amps at 120 volts is 600 watts.  I figure any device that changes something takes 10% for overhead, so you could factor that in too.  In this case, your inverter would take 10% to change 120 volts to 12 volts to charge the batteries.

You can put the gennie and the batteries in the same bay if you vent the bay.  The batteries need to be positively vented to handle off-gassing during charging.  The generator needs venting for all sorts of obvious reasons (intake air, exhaust, heat, etc).  The black tank can need bay venting in case sewer gas is released at some point, which can itself be dangerous and flammable.  You need to vent the bay at the top and at the bottom, some bad gasses go up and some go down...

That's my take on things anyway.  Hope these ideas help.  I have no idea about the shunt thing, but I don't know why you would need it if you do things the way I suggested (disconneting the inverter for measurements)

Brian

[Sean]

Do I have to have a shunt on my batteries for my xantrex RV3000 to read them properly?

AFAIK, there has never been a Xantrex product with this number, so it is hard to answer your question.

Is it possible you have either the RV-3012GS or the RS3000?  I have manuals for both of those and can give you a more detailed answer if that's what you have.

Generally, a shunt is used to calculate "state of charge" (SOC), also known as battery capacity remaining.  In order to do this, the monitor (such as a Link-10, or Link-1000 or -2000 which also have inverter-control functions) must be programmed in detail with the specifics of your battery bank, then "initialized" to a known state.

The battery charger on the inverter does not utilize the SOC information -- it works strictly based on system voltage.  When the voltage drops below a certain point, the batteries are considered to be in a discharge cycle, and the charger will initiate a 3-stage charge cycle when it next has access to 120VAC.

I am using a coleman powermate 1850 (one 15 amp circuit) right now to charge m batteries, but it looks like Im only getting about 7 amps on the bulk charge. I know I im supposed to get lots more.... whats the deal?

How are you measuring the 7 amps?  Your PowerMate should provide roughly 1500 watts, which, if the charger is set up to use it, would produce roughly 100 amps DC at bulk charge, IF the batteries are discharged to the point where they can accept that much current.

HOWEVER, and this is a big one:  If your 450 amp-hours of batteries are the flooded cell type, the highest safe charge rate is 90 amps IF the batteries are below about 85% SOC, and only 45 amps above that figure.

When you configured the inverter, you should have set a maximum charge rate or a battery bank size to handle this.  Perhaps this is what is keeping the rate low.

Also note that 7 amps at 120VAC is closer to 70 amps at 12VDC, so if you are measuring on the AC side, this would account for the difference.

Lastly, remember that on many inverters, the charger will only use whatever power is "left over" after powering the loads.  If the inverter is set for a 15-amp circuit, but then you have 12 amps of load on it (such as an A/C or a DHWH), you'll have only a couple amps left over for the charger, which would also easily account for the low charge rate.

When I do get a better generator, how many watts do I need to take full advantage of my battery charging?

Again, I would need to know which inverter model you have.  Many inverters can charge at 150 amps DC, which requires a 20-amp circuit.

Also, can I put my generator, batteries, and black water tank in the same bay?

Flooded batteries can not share a compartment with anything that can produce a spark, and that would include any type of generator.

I would not put any kind of batteries in a compartment with a generator, because heat ruins batteries and generators produce heat.

As for the black tank, I would check with the manufacturer to know the maximum safe temperature if it is a plastic tank.  Remember also that anything vibrating against a tank can eventually wear a hole in it.

HTH,

-Sean
http://ourodyssey.blogspot.com

[Oregonconversion]

It is the RV-3012 and I have the remote RC-GS I think that's the one.

Ok I have has it set at 15amps so that may have been my problem as far as charging. Should I set it to 30 amps then?

Also, it will not bring the batteries down past 12V ever it will shut off the inverter. No matter what setting I have it on.  What's the deal with that?

Thanks

[Sean]

... I have has it set at 15amps so that may have been my problem as far as charging. Should I set it to 30 amps then?

Depends... on how much shore power is available, and whether or not all of it flows through the inverter, or if you have other loads also connected.

Generally you are best served by running all your loads through the inverter if you want the inverter to be able to make the most use of whatever power is left over for charging.  However, if you have items such as an electric water heater or an air conditioner, you might not want to wire those to the inverter, to reduce the chance that they might accidentally run off the batteries when no input power is available.

So what you set the inverter's shore input to would be the total power available minus an allowance for any load(s) not connected to the inverter.  Does that make sense?

It is a certainty, however, that if you have set the inverter's input power to 15 amps, that is the most it can use for battery charging AND whatever loads happen to be connected to it at the time.

Also, it will not bring the batteries down past 12V ever it will shut off the inverter. No matter what setting I have it on.  What's the deal with that?

The low battery cut-out (LBCO) on a 3012 is 10.5 volts for three seconds.  If it is truly cutting out at 12 volts, the unit has a problem.

BUT... you need to be careful where and when you are measuring the voltage.  The batteries may well be sitting at 12 volts with no load on them, and then as soon as something starts up, such as a fridge, the voltage will drop considerably -- quite possibly down to 10.5 or even less for the requisite 3 seconds.

Also, note that the voltage at the inverter can be quite a bit lower than the voltage at the batteries themselves, depending on the distance and gauge of wire used to connect the two.  So you need to measure the voltage at the inverter itself, and right before it cuts out -- after it cuts out, the measured voltage will immediately rise.

12.0 volts, BTW, is extremely low for a lead-acid battery bank -- when the voltage hits 12.0 (resting) you should be looking to charge them ASAP.

-Sean
http://ourodyssey.blogspot.com

[Oregonconversion]

OK so if I have a 30 amp input from shore power, and all I am running is a 15A AC and thats it, then I set the inverter cut off to 15A? or would I set it to 30A?

What is the lowest voltage I should generally start charging at?

I found these two charts....   They are the same accept the yellow /orange starts at 30% in one and 60% in the other.

[Sean]

OK so if I have a 30 amp input from shore power, and all I am running is a 15A AC and thats it, then I set the inverter cut off to 15A? or would I set it to 30A?

If you have a 15-amp A/C running separate from the inverter, then all you have left for the inverter (including the battery charger and any inverter-driven loads) is 15 amps, so that's what I would set it to.  However, if the A/C is not being used, you could then safely set the inverter up to 30 amps, so it will have more power available for battery charging.

All of this load management applies, of course, if you are connected to a 30-amp pedestal.  When you have a 50-amp service available, you should have plenty of headroom even on just one leg to run the A/C as well as having a full 30 amps available for the inverter.

Most bus conversions will need to be wired for 50-amp shore power -- a requirement if you have either more than five total circuits on board, or more than two thermostatically controlled appliances (e.g. an electric fridge and an A/C).  In this case, the simplest wiring scheme is to supply the inverter from one leg, and all non-inverter loads from the other.

What is the lowest voltage I should generally start charging at?

I found these two charts....   They are the same accept the yellow /orange starts at 30% in one and 60% in the other.

You should charge any time you have A/C power available.  If you are in a position of having to, say, start a generator to charge, you will probably get the most bang for the buck by starting your generator when the battery SOC drops to 50%.

Note that you need an SOC meter for this.  The voltage tables you listed are only useful if you can completely disconnect the batteries from everything for a period of at least two hours, and preferably overnight, then measure their voltage with a high-quality volt meter.  In practice, this is impossible (well, it would be for me, and most RVers, although I suppose it could be done by someone not actually staying in the rig).

The charts that you supplied are correct, but, again, they are not useful unless the batteries are disconnected.  The first chart is, as stated, for flooded batteries, and the second chart appears to be for AGM batteries.

-Sean
http://ourodyssey.blogspot.com

[Oregonconversion]

OK Im kind of confused.... So if I DO have a 15amp AC running on the inverter and I am plugged into shore power ( I just found out its only a 20 amp circuit) What should I set my cutoff at?


SO AGM "sealed batteries" are better at going to lower voltages?

Sounds like I will be making a 50amp connection and getting a battery monitor.

[Sean]

OK Im kind of confused.... So if I DO have a 15amp AC running on the inverter and I am plugged into shore power ( I just found out its only a 20 amp circuit) What should I set my cutoff at?

If all your loads (including the A/C) go through the inverter, and you are plugged in to a 20-amp circuit, you should set the inverter input to 16 amps.  You could try going to 17 or 18, watch for a few hours, and see if it trips.  (Conventional breakers are designed to support 80% of their handle rating indefinitely, and 100% for shorter periods.  80% of 20 amps is 16 amps.)

SO AGM "sealed batteries" are better at going to lower voltages?

It's not that simple.  Let's just say that "typical" flooded deep-cycle batteries should not be drawn down below 50%, whereas "typical" AGM deep-cycle batteries can be drawn down to just 10-20%.  However, the number of "cycles" you will get out of a set of batteries diminishes the further you draw them down.   A set that might give you 1,000 cycles at 50% DoD might only give you 200 cycles at 80% DoD.

-Sean
http://ourodyssey.blogspot.com