Understanding house batts and charging them

[I-RV]

Boowho
You fail to mention how you are measuring the voltage. Since only little more then 0.5 volts drop means 50% depletion! you need to measure directly at the battery terminals with a good digital voltmeter. Within your cabin's 12 volt circuit, there is current draw and minute voltage drops due to resistance of the lines. A DVM is a high input impedance device an does not produce any drop in its probe lines.

I ran two separate lines (voltage & ground) directly from the cabin batteries to a DVM called the "Volt Minder", which a settable alarm. There needs to be a fuse in the positive line right at the battery. Yes, the fuse has resistance, but if you draw no current, there is no voltage drop. The wires to the meter can be 16 or 18 gauge, since there is virtually no current draw. From my experience, the battery capacity drop from fully charged is non-linear. After getting down to around 12.27 volts, the drop slows down.

Also, when charging the batteries, the batteries acquire a surface charge. So for example, if your batteries were at 50% and then charged up to 75% when you removed shore power with no engine or generator, you would see a reading over 12 volts. This is miss-leading and does not tell you what the battery true voltage is. This surface charge will bleed off slowly and quite fast if some cabin item was on.

What voltage represents 50% is controversial. I have seen charts that go from 12.06 to 12.27 volts. You need to get the specifics from the the battery manufacturer if you can.

These batteries are deep cycle, which means that you can draw them down a lot and they can be recovered. Drawing down not more then 50% is a good idea, since you will then get more life out of the batteries. I follow this rule.

As mentioned by others, the inverter consumes current even if nothing is using it. I frequently forget and leave it on ( old age, II guess).

[Superchief]

Boohoo, before you equalize the batteries, you will want to take a gravity test to see if one or more. cells within a battery are way off from the others. Interstate Battery puts out a really nice instruction pamphlet on this topic. Craig

[Superchief]

Boohoo, is this the remote that you currently have? . Craig

[I-RV]

Specific Gravity testing of the battery cells is indeed a great test. Voltage testing is good if done right at the battery with a DVM. I do not have a ME-RC, but no matter how sophisticated it is, the readings will be incorrect unless a separate voltage monitor wire was run from it to the Inverter and then to the controller.

Since I do not have a ME-RC, I admit that I might be speculating. I would suggest taking the ME-RC reading with shore power disconnected and the Inverter off. I am very curious what you get then and also curious what you get with a separate DVM.

Hank

[Superchief]

Boohoo, the reason I asked if that was the remote that you had, because there is a low cutoff setting you can program in so you house batteries don't drop below a certain level. Craig

[boowho]

Originally Posted by Superchief

Boohoo, the reason I asked if that was the remote that you had, because there is a low cutoff setting you can program in so you house batteries don't drop below a certain level. CraigAttachment 51703

Yep, I have mine set to cut out at 12.2 volts.

I'm really gratified at how many of you have jumped into this thread with info/help/suggestions. Somethings I already knew but a LOT was/is new to me. The amazing thing to me is that in less than a week, there are five pages to this thread!!

I'm beginning to think that I was expecting a lot more capacity at 220 AH; thinking (mistakenly) that things like the furnace, lights, etc (all 12 V devices) would not consume all that much current.

I do have a DVM so I'm going to take some readings under the conditions that some of you have suggested. BTW, to the person that asked, yes I was running the furnace at the time I had the problem.

I don't have a SG type tester, but I do have a load tester which I'm going check out (after allowing to batts to "settle" awhile; without charging going on).

Herk, your info on current draw for various 12 V devices is great to have. I'm going to review the entire thread to make sure that I've responded to every "potential idea" that each of you has thrown out.

Boowho??

[boowho]

Originally Posted by Superchief

Boohoo, is this the remote that you currently have? Attachment 51689. Craig

That's it, Craig.

Boowho??

[boowho]

Originally Posted by Herk7769

So you have 220AH 6 volt batteries, right?
What model Trojans do you have?

Could you give me an idea of the Magnum model number?
The Magnum may not be "seeing" all the amperage being drawn from the battery bank.

There is no doubt in my mind (now) that the Magnum is only "seeing" the amperage that the Magnum itself is using (or inverting to 120V). The Magnum is "oblivious" to any other 12V devices and the current they draw.

Boowho??

[boowho]

Originally Posted by I-RV

Boowho
You fail to mention how you are measuring the voltage. Since only little more then 0.5 volts drop means 50% depletion! you need to measure directly at the battery terminals with a good digital voltmeter. Within your cabin's 12 volt circuit, there is current draw and minute voltage drops due to resistance of the lines. A DVM is a high input impedance device an does not produce any drop in its probe lines.

I ran two separate lines (voltage & ground) directly from the cabin batteries to a DVM called the "Volt Minder", which a settable alarm. There needs to be a fuse in the positive line right at the battery. Yes, the fuse has resistance, but if you draw no current, there is no voltage drop. The wires to the meter can be 16 or 18 gauge, since there is virtually no current draw. From my experience, the battery capacity drop from fully charged is non-linear. After getting down to around 12.27 volts, the drop slows down.

Also, when charging the batteries, the batteries acquire a surface charge. So for example, if your batteries were at 50% and then charged up to 75% when you removed shore power with no engine or generator, you would see a reading over 12 volts. This is miss-leading and does not tell you what the battery true voltage is. This surface charge will bleed off slowly and quite fast if some cabin item was on.

What voltage represents 50% is controversial. I have seen charts that go from 12.06 to 12.27 volts. You need to get the specifics from the the battery manufacturer if you can.

These batteries are deep cycle, which means that you can draw them down a lot and they can be recovered. Drawing down not more then 50% is a good idea, since you will then get more life out of the batteries. I follow this rule.

As mentioned by others, the inverter consumes current even if nothing is using it. I frequently forget and leave it on ( old age, II guess).

You make some good points for me to ponder.

Boowho??

[Herk7769]

This thread might also be helpful.

http://www.forestriverforums.com/for...itor-5436.html

[unyalli]

Originally Posted by boowho

There is no doubt in my mind (now) that the Magnum is only "seeing" the amperage that the Magnum itself is using (or inverting to 120V). The Magnum is "oblivious" to any other 12V devices and the current they draw.

Boowho??

As previously stated, if you want to know for absolutely sure where you are with your batteries you need one of these in the negative line just before the battery bank.


You wire it like this with JUST the battery bank on one side and everything else on the other so ALL current draw is measured.

Then you get a deice that connects to this shunt to do the monitoring.

Originally Posted by boowho

My "battery computer" is part of the Magnum 1200 watt inverter

Magnum has the Battery Monitor Kit that includes the shunt. If you don't have this shunt somewhere near the batteries in the negative line you have a "Inverter/charger computer" not a battery computer.

-Jeff

[boowho]

Originally Posted by unyalli

As previously stated, if you want to know for absolutely sure where you are with your batteries you need one of these in the negative line just before the battery bank.


You wire it like this with JUST the battery bank on one side and everything else on the other so ALL current draw is measured.

Then you get a deice that connects to this shunt to do the monitoring.


Magnum has the Battery Monitor Kit that includes the shunt. If you don't have this shunt somewhere near the batteries in the negative line you have a "Inverter/charger computer" not a battery computer.

-Jeff

Thanks, I just ordered the Magnum ME-BMK today, since it will be plug-and-play with my existing Magnum equipment.

Boowho??

[camaraderie]

Boowho...let us know how that works out. Looks like it is a great way to go if you have a Magnum inverter/charger which many do.

[I-RV]

In looking at the connection diagram at the Magnum site, there are sense wires going to the shunt but also to the batteries. To me this means that you will not only get actual battery current draw, but also a more accurate voltage reading (which is used for measuring battery discharge level). I for one will be most interested in the results that you get. Please keep us posted and flipping those pizzas.

[camaraderie]

Full system hookup and manual may be found here...see figure 2.1 on page 4.
http://magnumenergy.com/wp-content/u...v-A-ME-BMK.pdf

[chesterhull]

I know this probably isn't a super technical way if measuring, but I found this interesting:

When I am plugged in to shore power, I measure 13.46 volts at the battery bank. (Probably the Charger in Bulk mode)
When I unplug from shore, and run the generator, I measure 13.36.
When I turn off the generator, and run the engine, I measure 13.0 volts at the battery bank.

Now, I know the charger changes from Absorb (something like 14.4) to Bulk (13.46?) to Float (13.2?), but should the charge voltage at the battery bank fluctuate so much between sources? It was especially curious that the engine was the lowest. That could be due to the fact that the alternator was charging the chassis batteries first, and wasn't giving much voltage to the house batteries.

The reason I was checking all this was because even after being plugged into shore power for more than 48 hours, my battery bank was still only showing 12.8 volts. I got a specific gravity tester and found that some calls were bad. These we batteries I had just purchased! But after looking more closely, 2 of them were already more than a year old! So I took those back and bought new ones.

Anyway, it got me to looking into this, and I was following this thread. Thought I'd post my experience so far.

[camaraderie]

Originally Posted by chesterhull

I know this probably isn't a super technical way if measuring, but I found this interesting:

When I am plugged in to shore power, I measure 13.46 volts at the battery bank. (Probably the Charger in Bulk mode)
When I unplug from shore, and run the generator, I measure 13.36.
When I turn off the generator, and run the engine, I measure 13.0 volts at the battery bank.

Now, I know the charger changes from Absorb (something like 14.4) to Bulk (13.46?) to Float (13.2?), but should the charge voltage at the battery bank fluctuate so much between sources? It was especially curious that the engine was the lowest. That could be due to the fact that the alternator was charging the chassis batteries first, and wasn't giving much voltage to the house batteries.

The reason I was checking all this was because even after being plugged into shore power for more than 48 hours, my battery bank was still only showing 12.8 volts. I got a specific gravity tester and found that some calls were bad. These we batteries I had just purchased! But after looking more closely, 2 of them were already more than a year old! So I took those back and bought new ones.

Anyway, it got me to looking into this, and I was following this thread. Thought I'd post my experience so far.

It isn't fluctuating. The Two readings of essentially 13.4 are absorption phase charging of a battery that is probably more than 75% full. Bulk mode at lower state of charge would be in the 14.5 range. Both sources of current go through the same battery charger so the results are similar.
The 13.0 reading you are getting while you engine is running is NOT from your alternator...it is residual surface charge from your battery charger.
If you disconnect your negative terminal for 24 hours you'll get a reading of 12.6 or 12.7 as the surface charge dissipates.
So...the REAL issue is does your alternator charge your house batteries at all. Suggest you run your batteries down to around 12.2 volts and then turn on the engine. Let it run for a while...some systems will first charge the CHASSIS battery and then switch to the house bank. Take a reading of your CHASSIS battery a couple of minutes after you turn on the engine. You should see somewhere in the 14V range at the terminals.
If you run the engine for a while (give it at least an hour if you haven't been on the road and charging the engine batt in a while) and don't see voltage between 13.8 to 14.5 at the house bank terminals THEN you know you have a charging problem assuming your house was designed to be charged via alternator in the first place. With the alternator eliminated as the problem by your earlier test... it is most likely a wiring issue, a fuse issue or the ever popular bad terminal connection. Hope that clears up the issue and lets you track down how the prior set got murdered!

[boowho]

Originally Posted by camaraderie

Boowho...let us know how that works out. Looks like it is a great way to go if you have a Magnum inverter/charger which many do.

Will Do..... Again, I find the interest in this thread amazing.

Thanks to all.

Boowho??

[boowho]

Originally Posted by camaraderie

Full system hookup and manual may be found here...see figure 2.1 on page 4.
http://magnumenergy.com/wp-content/u...v-A-ME-BMK.pdf

Yep, already had downloaded it. Thanks.

Boowho??

[Superchief]

camaraderie and boohoo,

To find out if my alternator was charging my house batteries, I did as you suggested and ran the house batteries down to 10. I then tried to start the generator and it would not start. I then started the coach, which turned over right away, and drove home - 4 hour trip from where I was. I then checked the house batteries and they were fully charged, so with this limited test, I would say my alternator charges my house batteries. Yea!!!! Craig