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Old 11-15-2012, 11:57 PM   #101
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Default Re: Layout plan.

George,

I think 200ah of batteries is a little on the skimpy side. My 650w micro draws 1100w and you don't want to constrain that choice too much. It is very useful to have 2000w inverter capacity if you ever want to run some other small stuff concurrently or plug in a vacuum, hair dryer, toaster or other high draw. A 400ah bank is mostly to enable that large inverter draw without too big of a voltage drop.

Your solar panels, OTOH, are likely overkill for that 200ah bank. Wasting some money here?

I have a similar electric kitchen draw as yours and lots of pc, stereo, small electronics. I have no solar and do not need a genset as long as I get some alternator hours every four days or so. If I added a single 150w solar panel I could sit still forever.

I did not think it would work this well and I bought an eu2000i in lieu of solar panels when I did my design seven years ago. That genset has proven not to be required for any normal boondocks.

Dan
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Old 11-16-2012, 12:45 AM   #102
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Default Re: Layout plan.

George, nice little S/S to use as a base, but it is likely that you may change some bits and pieces after you start using the facilities.

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Originally Posted by d_bertko View Post
George,

I think 200ah of batteries is a little on the skimpy side. ..................

Your solar panels, OTOH, are likely overkill for that 200ah bank.

Dan
Dan, different strokes for different folks. I prefer to use my solar as the main source of battery recharge and have minimal space to easily add extra battery capacity. So because of that I have deliberately "over-sized" my solar to make sure that the battery gets a good charge when parked for an extended period and considers potential lack of solar charge due to shade, clouds, etc.

I must admit that my power use is rather frugal to what I see planned for on most US vans, (mainly fridge & LED lights) but again, different strokes for different folks.

I also have Honda EU20i, for "emergency" use and it has yet to be used on the van.

Rob P.
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Old 11-16-2012, 01:14 AM   #103
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Default Re: Layout plan.

Quote:
Originally Posted by d_bertko View Post
George,

I think 200ah of batteries is a little on the skimpy side. My 650w micro draws 1100w and you don't want to constrain that choice too much. It is very useful to have 2000w inverter capacity if you ever want to run some other small stuff concurrently or plug in a vacuum, hair dryer, toaster or other high draw. A 400ah bank is mostly to enable that large inverter draw without too big of a voltage drop.

Your solar panels, OTOH, are likely overkill for that 200ah bank. Wasting some money here?

I have a similar electric kitchen draw as yours and lots of pc, stereo, small electronics. I have no solar and do not need a genset as long as I get some alternator hours every four days or so. If I added a single 150w solar panel I could sit still forever.

I did not think it would work this well and I bought an eu2000i in lieu of solar panels when I did my design seven years ago. That genset has proven not to be required for any normal boondocks.

Dan
Thank you for your thoughts. In our previous RV we had the 120W solar panels and wished we have had more. This 120W power was only OK during the perfect weather. I had 300amphours of batteries and never got near the point of 50% discharge, we did use built in generator as necessary. This new Sprinter will have electric fridge which will consume quite more than the previously owned LPG one.

Based on our previous experience I put together the spreadsheet which reflects our usage pattern - plus minus. For example, I don’t anticipate using over 1000W of inverter power and already purchased the Magnum MMS 1000W, the same one which Dave is using in his conversion. I had the 1500W Sine inverter before and never reached its limit. Our plan is to use the Origo alcohol stove and microwave without the shore power, with the shore power we can us the Origo electric coil.

Adding additional 200Amphours of AGM battery will weight 120lbs for $500 plus placement issue under the van. At absolute minimum I would have 200W solar which would save me $430 ($260 on the panel and $180 on the smaller charge controller) and 24lbs in weight against 3 panel 300W system. So, the additional battery will cost $70 more and weight 100lbs more than the additional 100W to get to the total of 300W of solar.

George.
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Old 11-16-2012, 06:47 AM   #104
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Default Re: Layout plan.

George,

Solar was pretty expensive back when I built my DIY---the gennie seemed to make more sense for a northern shade camper like me. So my spreadsheet always figured that even when the cost came down it should still be considered mostly a supplement.

The reasoning here is that I start with 420 ah of charged bank (2520 w-hrs to 50% SOC) and have a usage of 600 w-hrs per day. That gives me about 4 days use to 50% SOC. (Long weekends accounted for!) Then I should plug in to shore power, run a gennie, or drive some miles. The 150a alternator represents something like a kw of charging capacity. The key here is that many B owners like me are mobile enough to negate the need for more ah's.

Assumptions
Your chart showed worse consumption than mine--900 w-hrs vs my 600 w-hrs.
You are starting with 1200 available w-hrs from your bank (to 50% SOC)
If you drive once a week then any w-hr deficit is quickly erased by the alternator time.

So if you drive somewhere just once a week then you can reduce your solar requirement by 170 w-hrs a day (1200/7). If your driving was any more frequent, say once every 4 days, then the solar budget would get reduced by 300 w-hrs/day. (With my bank and usage rate that works out to zero solar requirement)

So your 300w x 4.5hrs = 1350 w-hrs/day is too much to meet a stationary demand of 900 w-hr/day. A more typical demand of 730 w-hrs (drive once a week) or 600 w-hrs (drive twice a week) would suggest you're spec'ing too much panel.

Well, that's the reasoning. I obviously capture twice the alternator w-hrs with a bigger bank. And even with electric fridge, micro, mag induction burner I still average about 2/3 of your projected demand. (My guess is that your estimate is too high.)

So with the price of panels dropping by 20%/year I would still advise starting with less solar and adding it if you found you needed it. Stealthier that way, too. Go ahead and get the bigger controller if it makes you feel better about a future upgrade.

Hard to argue that your system is cheaper than mine since apparently solar would be just a luxury use for me. Maybe in five years when solar panels and controllers cost $.25/watt

Wind resistance at 50 mph ballparks at 1 hp/sq ft of frontal area---maybe $400 of extra fuel over 200k miles for one sq ft of solar frontal area. I figure that is not too much different from the weight penalty of two extra batteries carried for the same miles.

No objection to you spending your money on extra panels---mostly wondered if you factored in the alternator time in your planning. Often much different than how a big rig camps.

Dan
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Old 11-16-2012, 08:45 AM   #105
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Default Re: Layout plan.

If I may.... what kind of fridge is that? 24ah/day seems low...... I also agree with the sentiment that 200ah is a little low. Batteries last a LOT longer if they don't have to work too hard. In your scenario I would go 400. Not sure about your location, but if you're near Eastern PA I can direct you to the scratch and dent sale at one of the local battery factories. Not too long ago I picked up 4 8-D AGM's for $600....(1000 ah)
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Last edited by oscarvan; 11-16-2012 at 08:50 AM.
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Old 11-16-2012, 03:18 PM   #106
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Default Re: Layout plan.

Quote:
Originally Posted by oscarvan View Post
If I may.... what kind of fridge is that? 24ah/day seems low...... I also agree with the sentiment that 200ah is a little low. Batteries last a LOT longer if they don't have to work too hard. In your scenario I would go 400. Not sure about your location, but if you're near Eastern PA I can direct you to the scratch and dent sale at one of the local battery factories. Not too long ago I picked up 4 8-D AGM's for $600....(1000 ah)
I ordered Indel/Webasto CR85 Isotherm http://isotherm-parts.com/PDF/manuals/cruise.pdf This manual claimed 0.8A average draw (43 degree F inside – 72 degree F ambient) so I increased it to 1.0A average assuming higher ambient temperatures. I am sure that with higher ambient temperatures this number will go up.

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Old 11-16-2012, 04:49 PM   #107
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Default Re: Layout plan.

Quote:
Originally Posted by d_bertko View Post
George,

Solar was pretty expensive back when I built my DIY---the gennie seemed to make more sense for a northern shade camper like me. So my spreadsheet always figured that even when the cost came down it should still be considered mostly a supplement.

The reasoning here is that I start with 420 ah of charged bank (2520 w-hrs to 50% SOC) and have a usage of 600 w-hrs per day. That gives me about 4 days use to 50% SOC. (Long weekends accounted for!) Then I should plug in to shore power, run a gennie, or drive some miles. The 150a alternator represents something like a kw of charging capacity. The key here is that many B owners like me are mobile enough to negate the need for more ah's.

Assumptions
Your chart showed worse consumption than mine--900 w-hrs vs my 600 w-hrs.
You are starting with 1200 available w-hrs from your bank (to 50% SOC)
If you drive once a week then any w-hr deficit is quickly erased by the alternator time.

So if you drive somewhere just once a week then you can reduce your solar requirement by 170 w-hrs a day (1200/7). If your driving was any more frequent, say once every 4 days, then the solar budget would get reduced by 300 w-hrs/day. (With my bank and usage rate that works out to zero solar requirement)

So your 300w x 4.5hrs = 1350 w-hrs/day is too much to meet a stationary demand of 900 w-hr/day. A more typical demand of 730 w-hrs (drive once a week) or 600 w-hrs (drive twice a week) would suggest you're spec'ing too much panel.

Well, that's the reasoning. I obviously capture twice the alternator w-hrs with a bigger bank. And even with electric fridge, micro, mag induction burner I still average about 2/3 of your projected demand. (My guess is that your estimate is too high.)

So with the price of panels dropping by 20%/year I would still advise starting with less solar and adding it if you found you needed it. Stealthier that way, too. Go ahead and get the bigger controller if it makes you feel better about a future upgrade.

Hard to argue that your system is cheaper than mine since apparently solar would be just a luxury use for me. Maybe in five years when solar panels and controllers cost $.25/watt

Wind resistance at 50 mph ballparks at 1 hp/sq ft of frontal area---maybe $400 of extra fuel over 200k miles for one sq ft of solar frontal area. I figure that is not too much different from the weight penalty of two extra batteries carried for the same miles.

No objection to you spending your money on extra panels---mostly wondered if you factored in the alternator time in your planning. Often much different than how a big rig camps.

Dan
Dan,

Here is my perspective. Selecting and sizing charging sources versus batteries is the design tradeoff. Regarding charging sources my preference in this priority: solar, shore, generator and alternator. Sizing the batteries is dictated by space availability, serviceability and weight; including moving batteries around with harming my spine. In regards to van space utilization my strong preference is not to have batteries inside the van except the passenger seat compartment.

At 200Amphours my batteries are sized for 1.3 days with possible push to 2 days. With my charging source preference my focus is on the solar system which is sized for one day in the good weather. If the weather is not good I will use my Honda 1000W. If the weather is really bad we go home.

The additional air resistance induced by the solar panels would likely be negligible. Panels are 41” wide and about 64” long (3 x 20.7 +) placed towards the back of the van in the middle of the eddy section of the airflow, it is not the frontal area.

Yesterday I found a good deal on the Morningstar MPPT 45 which will allow me to go to 400W if necessary so with ordered panels I am almost set for solar install. I am hoping that I can run the solar cables without penetrating the roof like through the third brake light or along the rear door side.

George.
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Old 11-16-2012, 09:30 PM   #108
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Default Re: Layout plan.

If you want 255 amp-hr. 8D battery inside, it will fit between back of left rear wheel well and the back of the 144" WB van if you space it up 3". My Magnum inverter/charger is about 18" in front of the battery with disconnect/fuse and shunt between the two.
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Old 11-16-2012, 10:30 PM   #109
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Default Re: Layout plan.

To clarify the wind resistance calculation:

You definitely want to align the panels with the narrow side to the front---I think that was your plan anyway.

The frontal area would be the height of the panel x the width of the front edge. If the panel is 3.5" tall by 41"wide that would yield about 1 sq ft of frontal area.

Thus the 1 hp loss at 50 mph. (The loss at 70 mph goes up by the cube = 2.7 hp)

The frontal area calculation is a stand-in for the too-complex wind tunnel tests to get an accurate answer. But it is real enough. Skinny roof racks on compact cars can account for 5% of their fuel use. The hp loss on a Sprinter solar panel is similar in amount but only accounts for maybe 2% of its larger wind resistance. Still, every 1% adds around $400 in fuel costs over 200k miles. (Guesstimate would be 50 hp needed for Sprinter to cruise level at 50 mph---thus 1 hp is 2% of fuel use)

The good news for your design is that if the panels are aligned the extra length of additional panels adds a negligible amount of air resistance. It's all about the frontal area. Likely worth adding a deflector in front.

To clarify alternator use:

I never run the van in camp to generate amp-hrs. It's just that the van gets driven on errands and between stops and that generates (nearly) free ah's for the bank. My only nod to this is to have a bank big enough to capture that quickly and that suffices for my needs for four days. A side benefit of the 420 ah size is that it gives me the ability to run almost anything that plugs into a house outlet with the 2000w inverter. That 400+ ah bank size is thus a sweet spot for many DIY'rs. (Thanks to the rv forum for that design help back when.)

You've got some of your components already so I think your design is set. Just check to see if the microwave will run on your smaller inverter and from the smaller bank. You'll get a voltage drop from the large draw and if the bank is not 100% SoC the inverter could object to that. I have overkill with a 2000w psw and twice the batteries---it runs the 1100w input micro or the 1200w mag induction cooker without a problem at all levels over 50% SoC. (Don't know about below that SoC level as I haven't ever gone there camping.)

Dan
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Old 11-17-2012, 12:05 AM   #110
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Default Re: Layout plan.

Quote:
Originally Posted by d_bertko View Post
To clarify the wind resistance calculation:

You definitely want to align the panels with the narrow side to the front---I think that was your plan anyway.

The frontal area would be the height of the panel x the width of the front edge. If the panel is 3.5" tall by 41"wide that would yield about 1 sq ft of frontal area.

Thus the 1 hp loss at 50 mph. (The loss at 70 mph goes up by the cube = 2.7 hp)

The frontal area calculation is a stand-in for the too-complex wind tunnel tests to get an accurate answer. But it is real enough. Skinny roof racks on compact cars can account for 5% of their fuel use. The hp loss on a Sprinter solar panel is similar in amount but only accounts for maybe 2% of its larger wind resistance. Still, every 1% adds around $400 in fuel costs over 200k miles. (Guesstimate would be 50 hp needed for Sprinter to cruise level at 50 mph---thus 1 hp is 2% of fuel use)

The good news for your design is that if the panels are aligned the extra length of additional panels adds a negligible amount of air resistance. It's all about the frontal area. Likely worth adding a deflector in front.

To clarify alternator use:

I never run the van in camp to generate amp-hrs. It's just that the van gets driven on errands and between stops and that generates (nearly) free ah's for the bank. My only nod to this is to have a bank big enough to capture that quickly and that suffices for my needs for four days. A side benefit of the 420 ah size is that it gives me the ability to run almost anything that plugs into a house outlet with the 2000w inverter. That 400+ ah bank size is thus a sweet spot for many DIY'rs. (Thanks to the rv forum for that design help back when.)

You've got some of your components already so I think your design is set. Just check to see if the microwave will run on your smaller inverter and from the smaller bank. You'll get a voltage drop from the large draw and if the bank is not 100% SoC the inverter could object to that. I have overkill with a 2000w psw and twice the batteries---it runs the 1100w input micro or the 1200w mag induction cooker without a problem at all levels over 50% SoC. (Don't know about below that SoC level as I haven't ever gone there camping.)

Dan
Dan,

Thank you again for your points and interest in this project. We didn’t decide to install or not the microwave unit yet. In the past we used it rarely. If we do, I will likely select an efficient 600W unit with 850W input. The Magnum is full sine unit so it should not struggle with the low power microwave.

Regarding aerodynamics of my solar cells I believe that higher impact will be from the Maxxair Deluxe fan which will be mounted in the front portion of the van most likely completely disturbing the air flow in the back. The solar panels will start at about 58” from the front beginning of the flat roof.

George.
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