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Old 03-06-2013, 02:48 AM   #51
Graphite Dave
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Default Re: Best way to charge house batteries: Solar or Alternator

I never thought that I would be in the "new fangled" group and not in the "old school" group. I hate most of the new fangled electronic wizard stuff. In this case with a little bit of reading it is obvious that a 3 stage charger is a no brainer. Thanks for the two linkys. They simply explain why a 3 stage charger is better. If you are going to spend big dollars on a AGM battery it makes sense to charge it correctly. Either a second inverter or a DC to DC 3 stage charger is the correct system design. Whatever hardware is used it is logical to charge the house battery with a 3 stage charger with temperature compensation. Unfortunately it is difficult to prove the value of 3 stage charging. I will never know how much longer my battery will live with proper charging vs. alternator charging. I know it is longer but how do I prove it.
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Last edited by Graphite Dave; 03-06-2013 at 03:45 AM.
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Old 03-06-2013, 03:17 AM   #52
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Default Re: Best way to charge house batteries: Solar or Alternator

Batteries have specs. So do the chargers. I think it's a good idea to read them and also understand the 101 on the Sprinter's charging system before blindly spending large amounts of time and money based on assumptions and myths.

The vast majority of installations, including the factory aux option, use a simple isolator relay.

Some of these chargers cost as much as a high end AGM battery bank. None of them will double the life of your battery over alternator charging - of this I am certain.
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Old 03-06-2013, 03:29 AM   #53
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Default Re: Best way to charge house batteries: Solar or Alternator

Quote:
Originally Posted by NBB View Post
Batteries have specs. So do the chargers. I think it's a good idea to read them and also understand the 101 on the Sprinter's charging system before blindly spending large amounts of time and money based on assumptions and myths.

The vast majority of installations, including the factory aux option, use a simple isolator relay.

Some of these chargers cost as much as a high end AGM battery bank. None of them will double the life of your battery over alternator charging - of this I am certain.
...neither of them will give current until the key is turned either...

...and there is no guarantee that one's normal driving durations will meet the time required to fully charge or maintenance charging... which, from my experience from living full-time on batteries for 7 years... requires periodic 6-12 hrs charges.



ladies... you're on your own now... I'm moving on...








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Last edited by OrioN; 03-06-2013 at 03:32 AM.
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Old 03-06-2013, 03:40 AM   #54
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Default Re: Best way to charge house batteries: Solar or Alternator

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Originally Posted by Graphite Dave View Post
I never thought that I would be in the "new fangled" group and not in the "old school" group. I hate most of the new fangled electronic wisard stuff. In this case with a little bit of reading it is obvious that a 3 stage charger is a no brainer. Thanks for the two linkys. They simply explain why a 3 stage charger is better. If you are going to spend big dollars on a AGM battery it makes sense to charge it correctly. Either a second inverter or a DC to DC 3 stage charger is the correct system design. Whatever hardware is used it is logical to charge the house battery with a 3 stage charger with temperature compensation. Unfortunately it is difficult to prove the value of 3 stage charging. I will never know how much longer my battery will live with proper charging vs. alternator charging. I know it is longer but how do I prove it.
An additional important factor to be considered in the decision process is to forecast charge timing allocation by alternator, PV, generator, or shore power, like a pie chart. My driving distances to campgrounds are about 75-150 miles, making the charge by alternator pie slice small enough to large degree nulling staged charging advantages. A simple separation relay, I already have one installed by MB, will be cheaper and less complex than additional inverter or DC>DC charger.

If I recall correctly you also mentioned that your inverter>inverter charger is rarely used.

George.
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Old 03-06-2013, 04:06 AM   #55
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Default Re: Best way to charge house batteries: Solar or Alternator

The 135 watt solar panel with its 3 stage Morningstar MPPT controller is the primary source of charging. I only need to use the "vehicle" inverter when the sun does not shine. I only use shore power just prior to a trip to cool the refrigerator before I leave. That way I start with the house battery at 100% SOC. The second "vehicle" inverter is a backup system used only for gray days. I have used it about 6 times in two years. The "vehicle" inverter is useful to heat water and to charge phones/computers. If I do start it on gray days to send 120 volt power to the house Magnum MSS1012, the refrigerator runs on 120 volt AC instead of 12 volt DC. The additional $200 dollars to have 120 volt power while driving is definitly worth the expense. As a bonus I always charge the house battery with 3 stage charging which gives longer battery life. I will never know if the battery life is enough longer to justify the additional $200.00 cost. I like the flexability the system provides.
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Old 03-06-2013, 04:24 AM   #56
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Default Re: Best way to charge house batteries: Solar or Alternator

As another thing to throw into the mix, I'm hoping the EFOY methanol-based fuel cells get cheaper, and get a better dealer network, so one can buy the methanol cartridges without having to hit a mail-order shop. The fuel cells are expensive now, but if the price falls to a fairly reasonable level, it will become a very useful subsystem to have on hand to keep battery banks topped off.
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Old 03-06-2013, 05:03 AM   #57
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Default Re: Best way to charge house batteries: Solar or Alternator

And if you're considering LFP batteries... Don't even think of using an alternator to charge the thing (nor three stage chargers).


And the prices are dropping (now less than $0.50 per VAh)... I've never seen published prices like this for LFP batteries:
http://www.electricmotorsport.com/st..._win_400ah.php
A set of these is lighter, and triple the available power of an 8D AGM battery, with little voltage sag. These 400Ah batteries are 13.5 lbs each.

Information here..
http://www.electricmotorsport.com/st...n%20Manual.pdf

Last edited by brbarian; 03-06-2013 at 07:31 AM.
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Old 03-06-2013, 03:07 PM   #58
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Default Re: Best way to charge house batteries: Solar or Alternator

Quote:
Originally Posted by brbarian View Post
And if you're considering LFP batteries... Don't even think of using an alternator to charge the thing (nor three stage chargers).


And the prices are dropping (now less than $0.50 per VAh)... I've never seen published prices like this for LFP batteries:
http://www.electricmotorsport.com/st..._win_400ah.php
A set of these is lighter, and triple the available power of an 8D AGM battery, with little voltage sag. These 400Ah batteries are 13.5 lbs each.

Information here..
http://www.electricmotorsport.com/st...n%20Manual.pdf
Those batteries are 3.2v. Cost of $2400 for 400ah @ 12.8v is still 3x what I paid for Concorde Lifeline agms. Maybe 2x as expensive for usable SOC comparison. Maybe $100 fuel savings over 100k miles of use?

The lithium battery market is still immature but promising. Lots of technical tweaks and improvements still occurring. Don't think battery warranties will be worth much until the market shakes out to either big-cap firms or long-reputation ones.

Rule of thumb is that for every doubling of market size the mfr cost comes down 20%. Should be pretty cost competitive for most of us within five years.

Hoping my almost 8 y.o. (still going strong) agm bank lasts until a mass market develops for Li-ions (or their successors!)

Dan
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Old 03-06-2013, 03:18 PM   #59
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Default Re: Best way to charge house batteries: Solar or Alternator

The isolation relay is industry standard. Millions of motor homes use them. It's simple and it works.

What's the alternative? An inverter/converter configuration is mentioned to charge house battery. This sounds rather wacky to me. The efficiency is awful. Say we got a converter that outputs 50A, has a power factor of PF= 0.7 and is 80% efficient. The inverter is 90% efficient.

How big does the inverter have to be?

Converter output power = Pout = Vmax * Imax = 14.7V * 50A = 735W
Converter input power = Pin = Pout / (efficiency * PF) = 735W / (0.8 * 0.7) = 1312 W

To be safe, you need a 1500W inverter.

How much battery current do you need to drive inverter?

Inverter input power = Pinv = Pin / efficiency = 1312 / 0.9 = 1458 W

Battery current = Pinv / Vbat = 1458W / 13V = 112 A

This is crazy! You're asking the alternator to supply 112 A so that the battery is charged with 50 A. This is not a well thought out plan. At those type of loads, how long will the alternator last?

Cal

Quote:
Originally Posted by NBB View Post
The vast majority of installations, including the factory aux option, use a simple isolator relay.

Some of these chargers cost as much as a high end AGM battery bank. None of them will double the life of your battery over alternator charging - of this I am certain.
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Old 03-06-2013, 04:12 PM   #60
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Default Re: Best way to charge house batteries: Solar or Alternator

Not wacky or crazy if you do not need to use the system very often. Please note how infrequently I need to use the "vehicle" inverter. Maybe you know how to calculate how much out of pocket cost per 2 hour use 6 times a year? I think you will find the cost is negligible. You are absolute correct that the system is not efficient. Why is that a concern if it does not cost enough to worry about.
The current 600 watt inverter works fine because I have programed the house inverter to a maximum 30 amps charging current. If I build another van I would use a 1000 watt "vehicle" inverter to increase the charging rate, reduce the shower water heating time from 60 minutes to 40 minutes and be able to use a cheap 750 watt electric heater in the back while driving. Each of the 3 uses can only be used alone. A selector switch will be installed so I can only enable one choice.
Alternator on my 08 is 220 amps. 1000 watt inverter will require less than half the alternator output. I do not know what the maximum amperage the Sprinter uses by itself but doubt the combined load is anything close to 220 amps. I do know the Sprinter has an automatic electric air heater that draws high amperage on a cold morning when you ask for cabin heat with a cold engine. My Scan Gage shows a voltage drop of .5 when electric heater is running. Obviously I would not operate the "vehicle" inverter at the same time.
The primary reason I chose this design approach was to always charge the house battery with a 3 stage charger. I do not think it is smart to connect two different size, type and age batteries together for charging. I also think it is better to know the battery temperature to adjust the charging rate. Crazy. Do not agree.
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