Design Advice: Van Electrical System

[WanderingCanuck]

I've been spending a lot of time reading articles on batteries, charge controllers, load calculations, and all of the things in between and beyond.  To put it mildly, it's a little daunting - even with electrical engineering education.

Initially I was eyeing AGM batteries, as this seemed to be the most commonly discussed battery.  Then I came across LFP.  Though definitely more expensive and perhaps less forgiving, there seem to be some real advantages for the system I'm considering.  I can post my load calculations later if anyone is interested or if my numbers seem unlikely.

Here are some facts and figures (all values rounded up):

• 100 Ah @ 12V daily use, includes 20% buffer above calculated loads (35% discharge AGM = 285Ah, 70% discharge LFP = 150Ah)
• Vehicle alternator charging only, ideally with less than 2h of driving per day.  Some of this could be parked with higher idle if it makes sense.
• From my reading so far, it seems programmable DC-DC charge controller is the way to go and I'm not looking to start a debate on that, but welcome opinions that are helpful.
• 1500W - 2000W inverter for occasional use of hand blender (700W), Microwave (1000W), Kettle (1200W) - These are figured into the initial 100Ah figure
• I'm still deciding between an induction cooktop and propane, induction bringing my power requirements to 140Ah daily (AGM = 400Ah, LFP = 200Ah)
• Induction simplifies cooking - maybe?, but I'd have propane anyway for a furnace.  I'm beginning to talk myself out of induction.
• I'd be happy to add a second (or third?) high output alternator if that makes the most sense.  Where does the law of diminishing returns kick in here?
• I shy away from solar due to being at 44.5° N and in an area with plenty of clouds and snow fall in the winter.  Not to mention not wanting to draw attention to the vehicle.
• Products easily available in Canada or shipped to Canada are preferred. (This rules out much from Amazon.com)
• Cost is a factor, but reliability and very low maintenance are paramount.
• If possible, I'd like to keep batteries inside the always-heated living space without venting.  Is this acceptable (and safe) with LFP?  With AGM it seems they need to be vented, which means it is harder to keep them warm in the winter.  How is over-temperature in the summer dealt with?  Are ceiling vents enough if outside temperature reaches 40°C (104°F)?

Wow, that seems like a lot of information to start out a thread!  I'm looking for help putting all of this together into a comprehensive solution, including all of the "glue" between components.  I don't need my hand held forever, as I'm a smart guy.  I just need to start tying together some of the information I've gathered so far.

I understand everyone has opinions, and most are biased to what they use.  If you have something that works, or components that would fit into what I've described so far I'd appreciate an accurate account of your setup and experience.  But please don't use this thread to start a debate over what's the "best".

Thanks in advance for your time and knowledge.

 

[highdesertranger]

first off it's a good idea to hook the alternator to the system to charge while driving. but to run the engine when you have nowhere to go is just plain wasteful, doesn't matter how many alternators you mount on it. second, heating anything with electricity is very inefficient. third lithium batteries should not be discharged or charged below 32f. sounds to me like you need to heads south or rely on a generator. highdesertranger

 

[Trebor English]

Lead acid batteries are hard to charge.  They get real slow towards the end.  They really don't like partial state of charge cycling.  LiFePo take charge much more easily and don't seem affected by partial charging.  Flooded lead acid are cheaper, AGM and LiFePo are similar in price when equivalent systems are compared.  

All can be used inside.  Flooded lead acid will generate hydrogen but the non explosive non flammable concentration is not hard to maintain.  Big holes for venting aren't necessary.  

A big problem with LiFePo is that the protection circuitry will disconnect the charging source when it is full.  If you use it as a car battery that doesn't work.  The car alternator requires a battery in the circuit.  For an rv house battery that doesn't matter unless your solar charge controller is the kind that self destructs if it has panel voltage with no battery.  That really is a thing.

My bias, what I use, is one flooded lead acid "deep cycle" battery for everything including engine starting, fridge, and cell phone.  I use propane to cook.  If you want an induction cook top or an electric programmable pressure cooker those are reasonable choices.  They will be more expensive to install but free to use.  It sounds like you are on your way to making an informed decision.  I think that is the "best" way.

 

[RVTravel]

Trebor, what brand and size battery in AH do you use as your one battery? There was a guy on the old yahoo group that did that and even stored the battery inside the van (not in engine compartment).

 

[WanderingCanuck]

first off it's a good idea to hook the alternator to the system to charge while driving. but to run the engine when you have nowhere to go is just plain wasteful, doesn't matter how many alternators you mount on it.

I agree in spirit, but what if you are doing some other things at the same time when idling, like storing some of the engine's waste heat for later release? This offsets some of the propane used for heating. I haven't found much discussion related to this, so it might be uncharted territory or just plain impractical.

Though I did mention the possibility of idling to charge, my intention would be while actually driving somewhere. I just don't know how much driving it would actually take to recharge fully, and maybe I wouldn't want to just drive in circles to do it.

second, heating anything with electricity is very inefficient.

Are you referring to the induction cooktop? I admit I know very little about these, but it seemed more efficient than a resistive heating element. You're probably right though that anything that can be done with a combustible gas should be.

third lithium batteries should not be discharged or charged below 32f. sounds to me like you need to heads south or rely on a generator.

Heading south and/or using a generator is not in the equation at this point, unless there's a "whisper-quiet" generator I'm not aware of. I would sacrifice other things before I consider it.

As for the battery temperature, my intention would be to keep the interior well within the safe charge/discharge temperature for the LFP battery. I want to keep the interior temperature above the dew point for sure, and more likely a minimum of 50°F - 60°F to keep the interior moisture under control and avoid having things freeze. Should anything fail and cause this temperature to drop below the safe point, I'd have controls that would cut either the charging or discharging as necessary. The vehicle's starting/charging system would be completely isolated from the house system and simply running the vehicle heat would bring the temperature back up (eventually) to where the house battery could once more be charged. Since I'd like only to charge when the vehicle is running, there should be plenty of heat available to keep the battery at the optimal charge temperature even with temperatures well below freezing.

 

[user 423]

... when idling, like storing some of the engine's waste heat for later release? This offsets some of the propane used for heating. I haven't found much discussion related to this, so it might be uncharted territory or just plain impractical.

You would need a good sized heat 'battery' for this to work. Fluid circulated thru a heat exchanger attached to the engine that would then be stored in a tank. Not practical because all that would be too heavy to haul around. Or hot air could be circulated through a pile of bricks that would retain heat for 'a while', meaning you would need quite a lot of mass for it to last thru an entire frigid night. Not practical either because of weight.

 

[highdesertranger]

it takes hours to recharge a depleted battery off an alternator. like 6-8 hours and this is with the engine at 2k rpm or higher. in other words, highway speeds. I am not tying to discourage you only pointing out some facts. highdesertranger

 

[WanderingCanuck]

it takes hours to recharge a depleted battery off an alternator. like 6-8 hours and this is with the engine at 2k rpm or higher. in other words, highway speeds. I am not tying to discourage you only pointing out some facts. highdesertranger

Facts are good. That's what I'm after, even if they are initially discouraging. The challenge is to work within physical limitations and/or adjust the plan to suit.

Is it due to the limited maximum current that can be accepted by the battery under charge, or the output of the alternator? The current available to charge can be increased by having multiple high output alternators, can it not?

 

[highdesertranger]

no, the battery can only take so much so fast. the first leg can go pretty fast but after that it's slow going. highdesertranger

 

[WanderingCanuck]

You would need a good sized heat 'battery' for this to work. Fluid circulated thru a heat exchanger attached to the engine that would then be stored in a tank. Not practical because all that would be too heavy to haul around. Or hot air could be circulated through a pile of bricks that would retain heat for 'a while', meaning you would need quite a lot of mass for it to last thru an entire frigid night. Not practical either because of weight.

I understand that it would be a lot of space and weight. The question, which I was actually going to ask in another thread but since you brought it up, is "how much?". I wouldn't be trying to store heat for an entire night in below freezing temperatures, only to offset the propane heating. But hey, if I add enough insulation and start warm, maybe it would still be tolerable by morning. I'd like to find some research or experiments on this, or I might just have to try something out myself before I decide what all to implement.

 

[Weight]

If you don't know "what is happening around here", you should start with flooded batteries, the best value is a pair of golf cart batteries in series for 12 volts. Then you will learn about batteries and charging, and power management.

 

[user 423]

I wouldn't be trying to store heat for an entire night in below freezing temperatures, only to offset the propane heating.

What kind of vehicle and what type of propane heat? Forced air furnace with a thermostat in a motorhome or a Mr.Buddy in a van?

 

[musicman]

I've been spending a lot of time reading articles on batteries, charge controllers, load calculations, and all of the things in between and beyond.  To put it mildly, it's a little daunting - even with electrical engineering education.

Initially I was eyeing AGM batteries, as this seemed to be the most commonly discussed battery.  Then I came across LFP.  Though definitely more expensive and perhaps less forgiving, there seem to be some real advantages for the system I'm considering.  I can post my load calculations later if anyone is interested or if my numbers seem unlikely.

Here are some facts and figures (all values rounded up):

• 100 Ah @ 12V daily use, includes 20% buffer above calculated loads (35% discharge AGM = 285Ah, 70% discharge LFP = 150Ah)
• Vehicle alternator charging only, ideally with less than 2h of driving per day.  Some of this could be parked with higher idle if it makes sense.
• From my reading so far, it seems programmable DC-DC charge controller is the way to go and I'm not looking to start a debate on that, but welcome opinions that are helpful.
• 1500W - 2000W inverter for occasional use of hand blender (700W), Microwave (1000W), Kettle (1200W) - These are figured into the initial 100Ah figure
• I'm still deciding between an induction cooktop and propane, induction bringing my power requirements to 140Ah daily (AGM = 400Ah, LFP = 200Ah)
• Induction simplifies cooking - maybe?, but I'd have propane anyway for a furnace.  I'm beginning to talk myself out of induction.
• I'd be happy to add a second (or third?) high output alternator if that makes the most sense.  Where does the law of diminishing returns kick in here?
• I shy away from solar due to being at 44.5° N and in an area with plenty of clouds and snow fall in the winter.  Not to mention not wanting to draw attention to the vehicle.
• Products easily available in Canada or shipped to Canada are preferred. (This rules out much from Amazon.com)
• Cost is a factor, but reliability and very low maintenance are paramount.
• If possible, I'd like to keep batteries inside the always-heated living space without venting.  Is this acceptable (and safe) with LFP?  With AGM it seems they need to be vented, which means it is harder to keep them warm in the winter.  How is over-temperature in the summer dealt with?  Are ceiling vents enough if outside temperature reaches 40°C (104°F)?

Wow, that seems like a lot of information to start out a thread!  I'm looking for help putting all of this together into a comprehensive solution, including all of the "glue" between components.  I don't need my hand held forever, as I'm a smart guy.  I just need to start tying together some of the information I've gathered so far.

I understand everyone has opinions, and most are biased to what they use.  If you have something that works, or components that would fit into what I've described so far I'd appreciate an accurate account of your setup and experience.  But please don't use this thread to start a debate over what's the "best".

Thanks in advance for your time and knowledge.

A few things speaking from one engineer to another.  For using AGM , they like a higher voltage than fluid cells. They also will not last as long if used below their 50% level. You would probally need a dual alternator where you can make another regulator for it, the solar panels read about 19 volts. You could use an older altenator that uses an external regulator. The good batteries are rated to last 10 years but I've only checked the U.S. companies.

With a car style battery, they are meant for a lot of current for a short time instead of a constant smaller current. Your inverter will have a current drain that will be constant. 

With all that said, a much simpler approach would be using a generator. The inverter generators made by Honda are extremely affordable and really quiet.

Hope this helps. All should be available in Canada


Bill

 

[WanderingCanuck]

What kind of vehicle and what type of propane heat?  Forced air furnace with a thermostat in a motorhome or a Mr.Buddy in a van?

I'm thinking forced air propane.  Something like Propex HS2000.  This would be in a large van such as Ford Transit, Ram Promaster, Nissan NV2500.  I'm still evaluating those options, but you get the idea.  A "standard" panel van is also on my list, but I don't like the idea of never being able to stand up inside and I'm somewhere around 6'2".

I'd be going overkill on the insulation, but would likely be limited by roof height in all of the options.  I've considered having only a section down the middle with less insulation to facilitate headroom, but LOTS everywhere else on the ceiling/roof where I'd not be standing, and the same (or more) on the walls and floor (again, where I wouldn't be walking).  I'd have a partition sealing off the cab area with at least the same amount of insulation.

In considering extreme insulation, another topic for another thread no doubt, I'm also thinking about a heat exchanger for fresh air rather than directly venting my precious warmed air in the winter.

 

[WanderingCanuck]

If you don't know "what is happening around here", you should start with flooded batteries, the best value is a pair of golf cart batteries in series for 12 volts. Then you will learn about batteries and charging, and power management.

I've seen that advice elsewhere too, and it does sound much better than murdering more than $2k or so of LFP batteries. My hesitation with FLA would be that they need to be vented, and this is in conflict with extreme insulation and keeping the battery warm in temperatures down to -30°C (-22°F). That's an extreme for Southern Ontario, but does happen.

 

[tx2sturgis]

Head south in the winter about 1000 miles and most of those engineering problems you are working with will get a LOT easier and cheaper to solve. But, you said traveling south is not in the equation and neither is a generator.

Winter time up north, boondocking in a vehicle, full time, without solar PV or a generator, is gonna be difficult, and no amount of electrical engineering education applied to expensive, elaborate, high technology solutions will make the basic problems go away, given those limitations. 

You are probably gonna be stuck with doing it old-school: Very warm clothes, an extremely warm sleeping bag, maybe a thermal tent inside the van that you sleep in, and propane or other fuel used for heating and cooking. 

Shore power, if available, and an electric space heater would go a long way toward heating the interior. 

Of, course, you won't need any electricly powered food refrigeration, so there is that.

But, even one modest solar panel would help offset the drain of charging a laptop and phone, and powering LED lights in the evenings. I would say forget about a microwave oven, electric kettle, electric induction cooktop, and what's this about a 700 watt hand blender....really? 

But the guys here will try to help...that's what we do...and good luck.

Or just head south in the winter...hey I hear even some birds do that now!

 

[WanderingCanuck]

A few things speaking from one engineer to another.  For using AGM , they like a higher voltage than fluid cells. They also will not last as long if used below their 50% level.

For my calculations, I'm using 35% DoD (Depth of Discharge, if I'm not mistaken) for AGM. It looks like a lot of people don't consider that they can only use 35Ah of their 100Ah AGM battery. I wouldn't have known either if I hadn't done some initial research - mostly reading posts from here. When doing the math and considering higher discharge depth, LFP starts to look very appealing despite the higher initial cost.

With a car style battery, they are meant for a lot of current for a short time instead of a constant smaller current. Your inverter will have a current drain that will be constant. 

I wouldn't consider a regular car battery unless I was on a seriously "tight" budget, which I'm not. If I have an inverter, it will only be switched on when I'm using a device that requires it. In looking at the A/C devices in my load calculations, I'm wondering how many of them I really need anyway. I could get away without it for a long time and might be just as happy. Without my A/C loads and inverter my daily usage drops to about 70Ah, requiring 105Ah LFP (65% DoD) or 190Ah AGM (35% DoD) - I'm assuming that a cheap FLA would be the same DoD as AGM for longevity?.

With all that said, a much simpler approach would be using a generator. The inverter generators made by Honda are extremely affordable and really quiet.

Since my initial post I've done some preliminary searches for generators and there might be some that are quiet enough. I'll keep it on the list for now. Can someone tell me how/why a separate generator is going to charge the batteries faster/better than a seriously overkill (possibly custom) alternator arrangement and maybe 2 hours of driving per day? How long does the generator have to run for?

 

[WanderingCanuck]

Head south in the winter about 1000 miles and most of those engineering problems you are working with will get a LOT easier and cheaper to solve. But, you said traveling south is not in the equation and neither is a generator.

You are probably gonna be stuck with doing it old-school: Very warm clothes, an extremely warm sleeping bag, maybe a thermal tent inside the van that you sleep in, and propane or other fuel used for heating and cooking. 

But, even one modest solar panel would help offset the drain of charging a laptop and phone, and powering LED lights in the evenings. I would say forget about a microwave oven, electric kettle, electric induction cooktop, and what's this about a 700 watt hand blender....really? 

Ok, the hand blender was just thrown in at the end. It hardly qualifies as a necessity, not to mention that it's in my calculations as being used only 15 min/day (77Wh). My initial calculations were to see where I stand, and I'm alright with paring that down a bit if I can still be comfortable. And "comfortable" for me definitely has a smaller set of requirements than many others. I'd be happy to sleep at 10°C (50°F) in the winter. I'd also be happy to do it in the summer, but I'll have to do without A/C for sure

You really think solar would do much of anything where I am? Certainly more in the summer, but in the winter?

I suppose heading south might be in the equation some day, but I still need to work and I'm not prepared to go through whatever hoops there are to do that in the US as a Canadian citizen (or to become a US citizen, for that matter). Heading WEST _is_ an option, however. The west coast is much more temperate, but I'm not quite ready to do that yet. In the meantime I'm willing to accept a more complex and less comfortable solution for the location I'm in now.

I know I'm asking for a lot, but at least I'm not trying to do it on a $500 budget.

 

[SoulRaven]

Hi Wandering Canuck,

After reading this thread, I have to mention that it would be a good idea to remember that the dominant mind-set of the folks on this forum is to "follow the weather", and to use a LOT of solar.  

Reading the replies that you've received, I'd say you've received advice from knowledgeable people who are trying very hard to keep within your parameters.  You may not realize how restrained they are being!     But I do!  

I haven't helped you very much, but wish you the best in your endeavours.  We can't ALL hang out in the Arizona desert.  It'll start getting crowded, like Quartzsite in January.

Regards,

Pat

 

[John61CT]

Pro Tip to get more / better responses:

Best to ask a small number of questions on just one topic at a time, as specific as possible, relevant background details all in one post, don't assume we remember stuff from past (huge) posts (take too long).

TL;DR make things as easy as possible for helpers to help