alternator to charge house battery

[highdesertranger]

sitting and running your engine at 1200rpm to charge your batteries is far less than ideal by a long shot. much better would be a small generator and a battery charger. highdesertranger

 

[John61CT]

Yes, very expensive wear and tear on the engine, best to only use while driving.

LFP bank less so, in fact nothing else needed but 30-40 minutes a day with a good HO alt setup.

 

[Van Go]

Thanks again for your input.

 

[DLTooley]

As I understand it AGM's accept charge faster and therefore have advantages in non-solar, alternator setups.

"The leading advantages of AGM are a charge that is up to five times faster than the flooded version, and the ability to deep cycle. AGM offers a depth-of-discharge of 80 percent; the flooded, on the other hand, is specified at 50 percent DoD to attain the same cycle life."
http://batteryuniversity.com/learn/article/absorbent_glass_mat_agm

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I'd double check that with the specific manufacturer.  Wiring is also important, but just disconnecting the battery before you connect it to the CPAP is all the 'isolator' you need.

My 3 year old cpap has an optional 12v cable, the Phillips Respironics.  In my testing it used less than ten watts - less than half your specs.  That is without the humidifier.  Part of the savings come from current 'flex' settings which do not put out full pressure continuously.  Your actual pressure setting will matter.  My flex range is 12-18 and my 90% number is around 16.

The best set up is solar on a fla, but for your use I'd give it a try.  A shorter trip would be best.  You do want to make sure it gets up to 100% regularly, but not necessarily daily.  Your manufacturer should have info on that - hopefully the premium price also includes premium customer service.

Personally, I use an AGM starter battery, a red top, and my Walmart marine deep cycle house battery is holding up, but fading.  I am hoping it will hold out long enough for a competitive LiFePo4 option to arrive.

You can use one of these to monitor EITHER power in or power out.  I first monitored my load to get my numbers than switched it to the solar panel.  I have no idea how good of a product this is and there are other options.

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https://www.amazon.com/bayite-6-5-100V-Voltmeter-Multimeter-Amperage/dp/B013PKYAV6

 

[John61CT]

There is lots of incorrect information on that (unfortunately very popular site)

The faster part is only for the early Bulk stage

http://www.pbase.com/mainecruising/effect_of_charge_rate_on_agm_battery

 

[John61CT]

That bayite is limited to 20A and doesn't log AH

 

[DLTooley]

John61CTThere is lots of incorrect information on that (unfortunately very popular site)

The faster part is only for the early Bulk stage

http://www.pbase.com/mainecruising/effect_of_charge_rate_on_agm_battery

I think the author is charging from shore power, Bulk power is not constant current under typical solar conditions.  There is some conflation going on here between different charging phases, but I'm not qualified to parse it.

One would expect AGM's to also have a lower capacity tail as with FLA, it is not clear from the author's test where the rapid absorption ends.  He does get to 85% in one hour with the higher of his two charge rates.  Just speculating here, but getting to 90% on a daily basis instead of 100% isn't horrible. 

I'm having issues with the Bayite, haven't dug into them yet.

 

[John61CT]

> Bulk power is not constant current under typical solar conditions. There is some conflation going on here between different charging phases, but I'm not qualified to parse it.

Yes, Maine Sail is The Master, read and learn, if we disagree with something at our noob stage in the learning process means we need to find out where we've gone wrong.

The term constant current is a misnomer, Bulk just means the source is striving to get to a voltage and low resistance/SoC is allowing maximum available current to be accepted by the bank.

The bank chemistry and SoC determine when the transition to Absorb takes place, not the charge source, which in turn doesn't regulate charge rate, just voltage.

When Vabsorb is being held by the charge source, Amps accepted will rapidly decline over the next 3-5 hours "long tail" until endAmps is reached.

> One would expect AGM's to also have a lower capacity tail as with FLA, it is not clear from the author's test where the rapid absorption ends. 

It scales down on a curve, no sudden transition. Depending on current rate, 75-85% is where you usually would not bother burning dino juice, and even a small solar source can handle the rest, as long as it's still before noon or so.

> He does get to 85% in one hour with the higher of his two charge rates.  Just speculating here, but getting to 90% on a daily basis instead of 100% isn't horrible. 

Yes it absolutely is, deadly to longevity with lead banks, especially AGM. It is critical to do whatever it takes to get to 100% Full as defined by endAmps at least a few times per week, ideally every cycle.

Firefly Oasis is the only exception in lead, their chemistry will stand up to regular PSOC abuse.

And LFP of course, which has no need to get to Full at all.

 

[John61CT]

> my Walmart marine deep cycle house battery is holding up, but fading.  I am hoping it will hold out long enough for a competitive LiFePo4 option to arrive.

$600-800 per 100AH is as competitive as quality LFP is going to get for IMO at least a decade. And that's for bare cells, the way to go for longevity rather that so-called drop-ins.

Does not include shipping or the necessary protective electronics.

The price of a complete professionally put together system may well drop from current 7x per AH quality lead's price, to maybe 3-4x.

But don't hold your breath.

 

[DLTooley]

A Tesla power wall is $420 per 100 AH currently, with a charger, but not an inverter.

I'd pay $175 for a 50AH Lithium with a confidence in its quality. I could skip the inverter.

The cheapest way now is to scavenge the i8650 cells. I'm not spending time on that until a standardized array becomes available. I think I've got ten now from a known good laptop battery (the laptop itself died).

 

[John61CT]

Tesla is not LFP, very dangerous and short-lived NMC high voltage for EV use.

So even if I had found FOSS open-hardware reverse-engineered BMS

not to mention sane 12-24V configuration

I would not consider trying to adapt these for House use.

Until Elon comes out with a packaged system purpose-built for such usage.

And mucking around with even new 18650 style cells is IMO for me personally a waste of time. Second hand cells triply so.

If that's one's idea of a nice hobby science project, go for it but be safe !

 

[DLTooley]

We'll see how the market develops. I would hope that we have some small influence on it.

 

[John61CT]

The Tesla Wall in a house combined with Solar Roof tiling idea is the likely path other than DIY hackers.

The only mobile market of note will be yachts, for prestige value.

Camping is very similar in functionality, just not on the PR radar.

But one day I bet we see all-electric Tesla glamping vans!

 

[wagoneer]

If"n my health was in question I would find the money to get a generator for piece of mind. A decent one will run at least 6 hours on a tank.

 

[mpruet]

I wanted to boondock a lot on my Alaska trip and my wife uses a cpap.  I found a converter which would take 12volt DC and convert it to 24 volt DC.  This was made by ResMed and would plug directly into her cpac. I got four MightyMax 35 AmpHour batteries to act as the source power.  It only depleated the battery by 15% each night.  Since I only boondocked three nights in a row, we were able to get to a campground and recharge them when I had power.

The converter is way more efficient than going through an inverter.

 

[John61CT]

Tesla batts burn, even with all the super high tech protection gear in place

http://www.diyelectriccar.com/forums/showthread.php?p=958082

People playing at putting House banks together for mobile use, from junkyard stripdowns of the power packs,

not just Tesla, from any electric vehicle

or building up their own from 18650 cells

are literally playing with fire. 

IMNSHO

 

[breeze]

I have a 2002 Toyota Tacoma 4-banger that I'm going to camp in for about 3 weeks. I need to charge an Optima house battery (blue top) from my stock alternator. I need the battery to run my CPAP machine (off a pure sine inverter). I need the simplest, cheapest way to do this. Would like to use the stock alternator. So, I think I run #6/8 copper from the alternator + pole to  some kind of switch. Manual switch  preferable since this is a short term hook up and I will probably leave the wiring in place. I would prefer to run copper back to the alternator ground. What brand parts should I get. Please, don't scold me. I have searched and found info but just need a simple, straitforward explanation of how to do this. BTW my machine runs on 24 volts (I guess in converts 120VAC) and lists draw as 1.25 A (FG) and 3.75 A (Sys)----I really don't know what the draw in amp hours will be. I will run it 8 hours a day.
I will have a 120 volt charger with me in case I have 120V at a campground, so I can top off the battery when possible. 
Please advise if this is not feasible. 
I don't have much $ to spend, but don't want to use cheapo parts. TIA.

For maybe the biggest part of the alternator/solar/plug in puzzle, the vehicle alternator(s) is(/are) the main ingredient, and I don't think a '4 banger' has enough umph to pull much more than itself.

Try to start from one of these vehicles to have a fighting chance:
https://www.nationsstarteralternator.com/Dual-Alternator-Kits-s/209.htm

Many member posters are covered in that selection. (Note: I have a bi-pap which is a cpap, but with a stronger input (or biway controlled.))

 

[John61CT]

Alternator is a very minor energy contributor for most people.

Unless you invest in LFP as well, or drive man hours every week, that money's better spent elsewhere.

 

[Charly]

I use a Samlex 160 ACR for charging the house battery when I am driving (I traveled and taught all around the country often) and have a solar panel charging too, through a Victron 75/15.

Found the ACR on Amazon Warehouse, open box for about $67. normal price is ~$90-100, and i still think it is worth it.

I have learned a lot from Maine Sail, and used to live right near them actually.

 

[breeze]

I use a Samlex 160 ACR for charging the house battery when I am driving (I traveled and taught all around the country often) and have a solar panel charging too, through a Victron 75/15.

Found the ACR on Amazon Warehouse, open box for about $67. normal price is  ~$90-100, and i still think it is worth it.

I have learned a lot from Maine Sail, and used to live right near them actually.

Do you have any specific links? TIA.