Tip 2 - Battery Sentry for boondocking

[I-RV]

When boondocking and just using the cabin batteries without the generator, we must be concerned about not discharging the batteries too much.

Well, what is too much; too-much is when you run the batteries really down and your appliances like your furnaces grind to a crawl. It is generally recognized that the batteries should not be discharged beyond 50% so that their useful life will be extended.

Unfortunately, the motorhome's status panel cannot give a good idea as to the discharge state. One convenient method is to measure the battery's voltage with a quality digital voltmeter (DVM) and compare against a chart such as below. If you can get a chart from your battery's manufacturer, that would be best. See chart for Trojan...........
Trojan Battery Company

To measure the cabin's battery voltage, it can be measured only at the battery terminals with your DVM or accessorize your Magnum Inverter with a $190 ME-RC Remote Control, plus a $180 ME-BMK Battery Monitor Kit. These are great additions if you want to go that route and they add a lot of programmability to the Magnum's charging sequences.

However, a low cost alternative (which I used) is the Volt Minder which costs between $25 and $45 (see photo). I found it to be within 0.07 volts of my quality DVM which is within 0.5%. It also has a settable alarm level, which will beep when the batteries go under the set voltage.

A word of caution; when using the Volt Minder or a separate DVM, the measurements must be taken at the battery terminals. I cut the cigarette lighter plug off and ran two wires directly from the battery terminals. The positive side must have a fuse right at the battery. The wires can be 18 or 20 gauge speaker wire. Since there is very little current drawn over these wires, there is practically not voltage drops.

They changed the Volt Minder a bit and can be found at:
Digital Voltmeter | VoltMinder.com

Battery's seem to be low-tech, but they are somewhat complex and are affected by temperature and a long list of items. My tip isn't meant to go into this deep dark cave, but only to offer you a simple, economical and somewhat precise way of monitoring your cabin batteries discharge state; especially when you are boondocking.

[boowho]

Originally Posted by I-RV

When boondocking and just using the cabin batteries without the generator, we must be concerned about not discharging the batteries too much.

Well, what is too much; too-much is when you run the batteries really down and your appliances like your furnaces grind to a crawl. It is generally recognized that the batteries should not be discharged beyond 50% so that their useful life will be extended.

Unfortunately, the motorhome's status panel cannot give a good idea as to the discharge state. One convenient method is to measure the battery's voltage with a quality digital voltmeter (DVM) and compare against a chart such as below. If you can get a chart from your battery's manufacturer, that would be best. See chart for Trojan...........
Trojan Battery Company

To measure the cabin's battery voltage, it can be measured only at the battery terminals with your DVM or accessorize your Magnum Inverter with a $190 ME-RC Remote Control, plus a $180 ME-BMK Battery Monitor Kit. These are great additions if you want to go that route and they add a lot of programmability to the Magnum's charging sequences.

However, a low cost alternative (which I used) is the Volt Minder which costs between $25 and $45 (see photo). I found it to be within 0.07 volts of my quality DVM which is within 0.5%. It also has a settable alarm level, which will beep when the batteries go under the set voltage.

A word of caution; when using the Volt Minder or a separate DVM, the measurements must be taken at the battery terminals. I cut the cigarette lighter plug off and ran two wires directly from the battery terminals. The positive side must have a fuse right at the battery. The wires can be 18 or 20 gauge speaker wire. Since there is very little current drawn over these wires, there is practically not voltage drops.

They changed the Volt Minder a bit and can be found at:
Digital Voltmeter | VoltMinder.com

Battery's seem to be low-tech, but they are somewhat complex and are affected by temperature and a long list of items. My tip isn't meant to go into this deep dark cave, but only to offer you a simple, economical and somewhat precise way of monitoring your cabin batteries discharge state; especially when you are boondocking.

I (for one) appreciate you tips. Keep 'em coming!!

Boowho??

[frankatp]

I just posted a question on boondocking and appliances run by the inverter. You guys may know the answers. Thanks Frank

[I-RV]

Originally Posted by frankatp

I just posted a question on boondocking and appliances run by the inverter. You guys may know the answers. Thanks Frank

I am not sure what outlets are powered by the inverter. In my 2012 390BH, I believe only the main TV and the outlet for the optional outdoor TV. For sure, the microwave is not powered by the inverter.

I have a propane/ electric refrigerator. Newer Berkshires with residential refrigerators are powered by the inverter and I do not know what else.

I hope this helps or someone else chimes in.

[acadianbob]

Originally Posted by I-RV

A word of caution; when using the Volt Minder or a separate DVM, the measurements must be taken at the battery terminals. .

Can you expand on why this is true. I just hooked my Volt Minder right into the buss on the converter. It seems to work fine there.

[Herk7769]

Originally Posted by acadianbob

Can you expand on why this is true. I just hooked my Volt Minder right into the buss on the converter. It seems to work fine there.

My guess is that you really have no idea what the voltage drop is across the intervening wiring. Since you are measuring battery health in fractions of a volt, your battery may be "healthier" than your minder is indicating.

[I-RV]

Originally Posted by acadianbob

Can you expand on why this is true. I just hooked my Volt Minder right into the buss on the converter. It seems to work fine there.

Hi Bob & Herk
The Volt Minder will read a DC voltage no matter where you plug it in. However, to get an accurate reading of the cabin batteries, it must be wired directly to the batteries. At any other place where there is 12 volts, there is voltage drops, caused by the current being drawn by your motor home. The Volt Minder draws very little current and is why thin gauge wire can be used and the length of wire is of no great concern. Since if for example there was a 0.5 volt drop between the battery terminal and if the Volt Minder was connected other than at the batteries, that would give you a false indication of almost a 50% depletion of cabin battery capacity.

Granted, there is huge wires between the Inverter and the battery bank and the voltage drop may be small. But Even Magnum offers the $180 ME-BMK Battery Monitor Kit which has separate voltage monitor wires going directly to the cabin battery terminals.

Magnum and I are therefore in agreement as to where to attach voltage monitor sense wire.