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Discussion Starter #1
Lots of talk here about auxiliary batteries. Lots of good ideas for installing and charging too!

Everything I've read says the best way to get long life from your aux battery is to not discharge it too much.

I'm wondering if anyone here uses a device to monitor battery level to help keep from discharging too much...

I have seen a few "shut off the power when the battery gets low" units, but they seem to be $$$.

Ed
 

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Many of the high end brands of inverters sell their own standalone battery monitors. Here is a good one: Victron BMV-700 http://baymarinesupply.com/store/victron-bmv-700-battery-monitor.html

Some sell a separate monitor screen like the one I got for my Magnum inverter: Magnum ME-RC50 http://www.tacticalwholesalers.com/Magnum-ME-RC50-Remote-Panel-With-50-Cable-ME-RC50_p_93233.html

Most solar charge controllers have a battery monitor function that shows on the controller itself or on a remote panel. I have the Morningstar TriStar TS-MPPT-45 with the TS-RM-2 Remote monitor screen.
 

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2014 Ram Promaster 2500 159" diesel
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Lots of talk here about auxiliary batteries. Lots of good ideas for installing and charging too!

Everything I've read says the best way to get long life from your aux battery is to not discharge it too much.

I'm wondering if anyone here uses a device to monitor battery level to help keep from discharging too much...

I have seen a few "shut off the power when the battery gets low" units, but they seem to be $$$.

Ed
Ed I saw the scrooge shingles so here's my go at this. You do need a volt meter, it is the only way to tell the charge state of a sla battery. Less than $5 on ebay shearch for:
LED Panel Digital Display Voltage Meter
And this should work for a low voltage cut off if your load is less than 30a, less than $20 on ebay also:
12V 30A PWM Solar Panel Charge Controller
This has the option to hookup solar panels of 30a or less, but to use it as a low voltage cut off just hookup the battery and the load. If you can't picture this, the only thing you have to do to your current setup, would be to cut the power leads from your rotating disco ball >:D and hook the ball side to load and battery side to battery and your good to dance the night away.
In another post you were asking about the dual battery isolator, if you don't have one you should get one you can get the old style tin can for about $45 or a new style VSR for $75
 

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Voltage and charge remaining in an AGM or flooded cell lead acid battery is not a linear relationship, that is, voltage will not drop proportional to electricity used. A fully charged lead acid battery with no load on it will display something like 14 Volts and with about 1/100th of the charge used up it is apt to drop to 12.8 or so but will remain close to 12 volts until perhaps 50 percent of the power is gone. When it drops to about 11.5 volts it is at 40 percent or so. That is too much discharge to occur regularly and keep the battery healthy. 60 percent is a better low level and batteries I have used read 12+ volts there. So here is my take.... if your battery reads 12 volts you should turn off the disco ball or begin charging. If it reads over 14 volts you have a topped up battery. Outside this range is not good. Kept in this range and used regularly they last for many years 7 to 10 is not unusual for a coach battery my current one is 8 years old and going strong.
 

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Hi,
Some may disagree with this, but I think for that if you are doing something like an RV where usage might be 30 days a year that figuring on a discharge of 80% is OK because you are just not putting very many cycles on the battery, and the lower cycle life for 80% discharge won't end up being a factor in your battery life.

The Trojan Battery website has a plot that shows number of cycles you will get vs depth of discharge. I can't find it right now, but my conclusion after seeing it is that using my PM as an RV something like 30 cycles a year, I will never get to the number of cycles they show -- the battery will die of something else long before then.

Designing for 80% discharge allows you to use smaller, lighter weight, less expensive batteries, and for RV type service there does not appear to be any down side.

Gary

PS: the Trojan Battery site has ton of good design info on batteries, and you can phone them with a question and talk to a tech person who actually knows batteries.
 

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I just wired in a digital $5 Amazon voltmeter directly to my aux AGM battery. It's always on and gives me immediate voltage info. The thingy next to it was a "gift" from the company I bought the dedicated AGM battery charger from. I connected it up because I had it but it's pretty useless and I' glad it was free.

 

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Discussion Starter #9 (Edited)
KWB,

While you were sending the reply, I was researching and stumbled upon a solar controller as you suggest - good idea, and affordable! I was thinking that if I hooked up a basic charger instead of solar panels, I could also use it to manage the charging when hooked up to AC. Only problem seems to be getting a manual for one of the $20 units. Some say adjustable parameters, but don't define what's adjustable. Need to know for AGM charging/discharging.

I found a 95AH AGM H8 battery at Advanced Auto for about $139. Always seems to be an online discount available there. That's going to be the one for me!

I plan to build a box bolted to the holes in the back of the uprights on the driver's seat. Should be pretty solid, and not prone to aerodynamics.

KOV, nice, and the price is right! Now if it could also turn off a relay at a certain voltage, that would be IT!

Thanks!
Ed
 

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Ed, I bought a dedicated AGM charger for about $75 and hard wired it to my AC in receptical so whenever I was plugged into the grid it would charge the house battery. I added a shut off switch in the cable from the house battery to the starting battery so I could keep them seperate if I wanted to, for example so as to only charge the AGM from the battery charger and not the starting battery. It works fine and will actually charge them both if I have them combined but the starting battery is flooded and not a AGM so preferable they shouldn't be charged together. When I get my solar up and running I don't expect to have to combine them again under normal conditions as the PV should keep the house battery charged. Time will tell of course if it will be enough.

If you want a link to the AGM charger I used I can dig it out for you.
 

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Ed try this search on ebay for about $30 volt meter onboard.
LCD 10A 20A 30A MPPT Solar Panel Battery Regulator Charge Controller

You can't power a charger with a charger it won't work. You would need a 18 to 20 volt power supply with at least 10amp.
 

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Ed, I missunderstood what you wanted to do, sorry. I was thinking you just wanted to be able to charge it from the grid with a regular AGM battery charger.

Your alternator is perfectly capable of charging both batteries at once but the AGM should be charged at a different rate than the flooded or it will overcharge. I only charge them both from the alternator while I'm running the inverter as it eats up so much power neither battery will ever get fully charged correctly. This is one reason I'm putting the solar in just to keep the AGM fully charged (hopefully) and seperate from the alternator charging. It sounds as if the idea of using a cheap solar controller to charge the AMG battery from the alternator is a good, inexpensive way to protect the AGM.

The great thing about all this is the fact that there are many ways to accomplish the same goal and everyone has their own pet ideas and solutions and there is nothing that time and money can't cure!
 
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