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Old 05-06-2014, 06:55 AM   #51
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Originally Posted by boowho View Post
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.

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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.

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Originally Posted by boowho View Post
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.

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Old 05-06-2014, 09:09 PM   #52
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Originally Posted by unyalli View Post
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??
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Old 05-06-2014, 10:01 PM   #53
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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.
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Old 05-07-2014, 08:12 AM   #54
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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.
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Old 05-07-2014, 10:03 AM   #55
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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
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Old 05-07-2014, 09:52 PM   #56
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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.
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Old 05-07-2014, 10:17 PM   #57
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Originally Posted by chesterhull View Post
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!
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Old 05-08-2014, 12:49 PM   #58
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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.

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Old 05-08-2014, 12:50 PM   #59
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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.

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Old 05-10-2014, 08:53 PM   #60
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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
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