Alternatives to APU
06-21-2021, (Subject: Alternatives to APU ) 
Post: #1
Alternatives to APU
Reading the thread about diesel generators got me thinking about alternatives. I know there are at least one, maybe more, battery based APU's out there. Recently I've been thinking about going this route but building my own system to meet my needs. Figured I'd share and see what others have for feedback...


The newest plan is looking like a 2nd battery bank, a maxwell ultra cap, some solar (eventually) like Waterloo has and the smallest A/C I can find that fits my needs. My inverter can take AC shore power to pass through and charge the batteries too. Also need to replace my alternator so I'll be upgrading to something appropriate. I don't spend much time in the truck, 4-5 nights a week at most and home weekends, so I don't need that much power or cooling. Unfortunately the over night load is currently bringing the batteries down into the 12.3-12.6v range and the truck doesn't start as smoothly when it drops below 12.4v Been looking at those LiFePO4 (Lithium Iron Phosphate) batteries recently for the bunk, various different brands. Seems a bit pricey up front but should make sense over the lifetime, especially for my setup. I've only been getting about 1.5-2 years out of a set of "deep cycle" AGM's with my usage habits and the LiFePO4 should last significantly longer.

Right now I have 4 deep cycle/starting AGM batteries, about 15 months old. I think one is going bad and I plan to swap it for the maxwell cap. I'll keep the 3 good AGM's to run the truck and act as a backup to the ultra cap and add a second bank with the LiFePO4 batteries just for the bunk, Inverter and AC. Probably wire in a manual switch to connect the AGM's to the bunk for emergencies. Eventually I'll add the solar, more as a failsafe to keep the batteries charged if the truck sits for an extended vacation or something. Keep the fridge cold.

Only real downside to the LiFePO4 batteries is the charging/discharging temperature ranges. Typically discharge -4F-140F with charging between 32F and 140F. I've seen some with built-in heaters, but with 3ish months of 32F and below temps where I am it's something to carefully consider.

I like to take my time thinking about things and get feedback from others before I put a plan like this into motion. And yes, I realize this solution wouldn't be much savings over other options, but it would be lighter, more compact, quieter, and more fuel efficient (?) than a generator. It would also be tailored to my own needs and fully serviceable by myself.


User's Signature: "The sky above the port was the color of television, tuned to a dead channel." – William Gibson, Neuromancer
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06-21-2021, (Subject: Alternatives to APU ) 
Post: #2
RE: Alternatives to APU
How those LiFePo batteries will survive vibration?
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06-21-2021, (Subject: Alternatives to APU ) 
Post: #3
RE: Alternatives to APU
Just make sure you're using a BMS to keep it maintained.
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06-23-2021, (Subject: Alternatives to APU ) 
Post: #4
RE: Alternatives to APU
So take this with a large grain of salt {garbage product removed} I get an email from these people about once a month. I have had no contact and know nothing about them. That said it appears they are using the driveshaft to belt drive an alternator to charge up a battery bank. Poke around on your own.

They seem to make some efficiency claims. I would be skeptical because there is no free lunch. The benefit with this system MIGHT be simplicity

I wonder if you could put some magnets on the drive shaft and put an armature around it. And generate electric power that way. Sort of like this.

https://youtu.be/LYQ2PiX_Z9o Good project for Rawze.
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06-23-2021, (Subject: Alternatives to APU ) 
Post: #5
RE: Alternatives to APU
My truck came with an electric powered a/c. I took the cheapest route, with 4 starting batteries, and 4 deep cycle. Just plain old flooded lead batteries. I have a blue sea systems automatic charging relay that connects the deep cycles to charge when the truck is running. I'm not sure what I was thinking, but I ran my inverter cable to the starting battery bank, so I get nervous if I'm on a 34 and have made a few cups of coffee and ran the fridge and tv for a day and end up idling for a few hours to make sure they're topped off.

I've thought about switching to AGM's every summer when I test and replace the underperforming ones. This year I replaced 5, but it was still cheaper than buying 2 quality AGM's.
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06-23-2021, (Subject: Alternatives to APU ) 
Post: #6
RE: Alternatives to APU
(06-23-2021 )Nostalgic Wrote:  My truck came with an electric powered a/c. I took the cheapest route, with 4 starting batteries, and 4 deep cycle. Just plain old flooded lead batteries. I have a blue sea systems automatic charging relay that connects the deep cycles to charge when the truck is running. I'm not sure what I was thinking, but I ran my inverter cable to the starting battery bank, so I get nervous if I'm on a 34 and have made a few cups of coffee and ran the fridge and tv for a day and end up idling for a few hours to make sure they're topped off.

I've thought about switching to AGM's every summer when I test and replace the underperforming ones. This year I replaced 5, but it was still cheaper than buying 2 quality AGM's.

did you make a another battery well on the other side of the truck?


User's Signature: We're a full grid off.
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06-23-2021, (Subject: Alternatives to APU ) 
Post: #7
RE: Alternatives to APU
Haven't looked at it yet, but right off the bat I can say that anything attached to existing mechanical systems will put an additional load on them. Even the magnets/armature idea. Ultimately the magnets are "pushing" the electrons around and just like anything else there is some resistance. So I don't see where the efficiency would come in, unless it's just the fact that you are repurposing existing components instead of adding even more parts? Ultimately either solution would be like attaching an additional alternator to the output of the engine.


User's Signature: "The sky above the port was the color of television, tuned to a dead channel." – William Gibson, Neuromancer
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06-23-2021, (Subject: Alternatives to APU ) 
Post: #8
RE: Alternatives to APU
(06-23-2021 )Nostalgic Wrote:  My truck came with an electric powered a/c. I took the cheapest route, with 4 starting batteries, and 4 deep cycle. Just plain old flooded lead batteries. I have a blue sea systems automatic charging relay that connects the deep cycles to charge when the truck is running. I'm not sure what I was thinking, but I ran my inverter cable to the starting battery bank, so I get nervous if I'm on a 34 and have made a few cups of coffee and ran the fridge and tv for a day and end up idling for a few hours to make sure they're topped off.

I've thought about switching to AGM's every summer when I test and replace the underperforming ones. This year I replaced 5, but it was still cheaper than buying 2 quality AGM's.

That was pretty much where my idea started. As I researched things, discovered and learned more it evolved into it's current form. Probably still has a fair amount of evolution yet to come too. That's mainly why I posted here, to get feedback, input and ideas which I can factor into my overall plan. Of course I make a lot of plans, but very few ever get put into motion. So we'll see where this goes. I'm also contemplating buying a trailer or 2 (currently renting one) and maybe buy another tractor. Partly as a spare, partly to expand. But that's a topic for a future thread, if I ever get serious about it.


User's Signature: "The sky above the port was the color of television, tuned to a dead channel." – William Gibson, Neuromancer
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06-23-2021, (Subject: Alternatives to APU ) 
Post: #9
RE: Alternatives to APU
(06-21-2021 )Nilao Wrote:  Just make sure you're using a BMS to keep it maintained.

Absolutely. Will need to draw up some diagrams and plan out all the components that I'll need.

Many (most?) of the non-chinese knock-offs have a BMS built into the battery, however I might need something else between the alternator and batteries or the inverter/charger and the batteries. Haven't gotten to that level of planning yet.

(06-21-2021 )snailexpress Wrote:  How those LiFePo batteries will survive vibration?

I don't think vibration is a large concern. They are currently in use in RV, Boat and PIV (Powered Industrial Vehicle) applications. I'd probably insulate them, mainly for thermal efficiency as they don't like freezing temps, which should also provide some level of vibration dampening.


User's Signature: "The sky above the port was the color of television, tuned to a dead channel." – William Gibson, Neuromancer
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