Can I use the alternator to charge batteries?

[KeyWestPirate]

As someone who teaches electrical theory, circuitry, and such, I don't buy this. With no load there is no draw.

Do you have a definitive source for your claim?
There IS an amount of power pulled just to run the inverter and that is pulled at any time it's on but it's a SMALL amount. The Victron 24/3000 MultiPlus all in one that we're going with is a 15 watt draw when there is no load.

My 5KW pure sine wave inverter draws only 25 watts of "housekeeping". Fans immediately come on if the load increases.


I believe that you should separate vehicle battery from house battery. The vehicle batteries are simply not constructed for this service. They are designed to put out extreme cranking amps for a few seconds, and be immediately recharged when the engine runs. The plates are super thin and easily damaged.



A house battery is designed to be discharged deeply, but any more than 80% consistently will shorten their life. It's a trade off. You can go to 50% but the batteries will not last as many years.


I personally don't see much difference between golf cart batteries and more expensive stationary batteries like Trojan. Sure, when you step up to Rolls Royce, but initial cost becomes more than a replacement in five years.


Golf cart service is what you will doing with your house battery, Hopefully,, not as deeply discharged as the battery in your golf cart.



And eventually,, you will wake up with a truck battery that won't crank your engine.


GC batteries at Costco were $85 the last time I made a buy. Start accumulating old cores. They don't care what it is or what it looks like, but if you don't have a core you are on the hook for another $15 per. That is Arizona, California might be more.

I buy 8 at a time (6 x 8 = 48) The other problem I see for bus use is,,other than being heavy,, access to check and add water, and keep the tops clean.



I've had good luck with LA, hard to kill GC batteries as long as they have enough water, and you religiously keep them charged after use.


Yes, you can charge your house battery inline with your vehicle battery. A switch is best, but a big silicone diode mounted to a metal wall for heat dissipation will work (but not as well because of the .7 volt drop across the diode. Cabling has to be rated for the charging load anticipated, and will have to be bolted or securely crimped to the diode.


I would avoid AGM and go with the same tried and true LA that you have in your Group 31 vehicle battery.

 

[TheHubbardBus]

I would avoid AGM and go with the same tried and true LA that you have in your Group 31 vehicle battery.

I would not want flooded LA house batteries in the interior of a moving vehicle for a multitude of reasons. There's nothing not tried & true about AGM, and if you're going the lead acid route, especially inside the vehicle, they offer numerous advantages (ie. resistance to leaks, spills, venting). Even outside, the increased charge/discharge rate is enough of an advantage to me. That's assuming you're stuck with LA. At this point (availability / price) LFP is hard to beat.

 

[KeyWestPirate]

I would not want flooded LA house batteries in the interior of a moving vehicle for a multitude of reasons. There's nothing not tried & true about AGM, and if you're going the lead acid route, especially inside the vehicle, they offer numerous advantages (ie. resistance to leaks, spills, venting). Even outside, the increased charge/discharge rate is enough of an advantage to me. That's assuming you're stuck with LA. At this point (availability / price) LFP is hard to beat.

All you say is true,, but they are NOT going to be in the interior,, rather in the basement. I had a large bank of AGM in a 45 Ft Beneteau that I owned years ago,, so yes the technology is tested. I had a Trace 4024 that both provided power from the batteries,, and managed their charging. Everything worked perfectly. I also had a Splendide washer dryer that worked very well too,, although the load capacity was small. We had a 50 GPM watermaker and a 7.5KW northern lights marine generator.


Getting back on topic: There is more and more lithium ion surplus coming available. Mostly from wrecked electric cars. That is what I will use in the bus. I dread inventing the wheel again after I have become so comfortable with LA. My wife and I were just talking this morning about how the farm system works so transparently and flawlessly.



But,, the world moves on. This is one source:


They have a lot of photos of Li Ion installations

https://batteryhookup.com/


Sorry about the bogus url posted earlier








There is nothing wrong with AGM. I just don't see the price advantage. They are more money.



They are more prone to damage from overcharging since the mat is a gel and not a liquid electrolyte,, and the mat is thinner.

 

[TheHubbardBus]

All you say is true,, but they are NOT going to be in the interior,, rather in the basement.

I thought we were discussing the OP's system/questions. Are his batteries going to be in the basement as well?

 

[KeyWestPirate]

I thought we were discussing the OP's system/questions. Are his batteries going to be in the basement as well?

I don't know. I assume as much infrastructure as possible will go into the basement. Electrical, Heating/Cooling, Tankage.


https://batteryhookup.com/products/25-9v-24ah-621-6ah-spim08hp-24v-power-module


The above could go under your bed. No smell, no gassing, no attention, just someplace where it won't get too hot. But why not in the basement next to inverter and solar controller?? Shorter cables.
Did I mention no need to add water ??



Pricing: A GC2 is 215 amps at 6V. Let's use Costco price of $85, and if you don't have a core,, it's $100. This Li Ion unit is 32 amp at 24V so,, the equivalent of a 128 GC2 for double the price (depending on that core).


That's not bad as it goes. These are touted as almost new. Li Ion if it's properly treated has a 20 year life. Plus you can discharge it to 20% or lower , consistently without damage,, much lower than LA. If you consistently discharge the battery to 20% and your LA to 80%, you have 4 X the working capacity in your Li Ion.


So, if you accept these numbers, and equivalencies,, used Li Ion can be had at the same price point as LA GC2 batteries.



At this point the numbers start to make sense. You need a BMS to manage and balance the individual cell voltages, not expensive. There are different charging requirements, but your controller manages that.


If you are starting from new,, buying new controllers anyway, it makes even more sense to go Li Ion



If you are close to Arizona,, and looking for solar panels,, this guy has good deals,, is very honest. His inventory changes as he gets left overs, surplus,, non UL, but the prices cannot be beat.



https://www.ebay.com/str/santansolar

 

[TheHubbardBus]

No, lithium ion doesn't make much sense at all as a bus house bank unless you really, really know what you're doing, and have a compelling reason to choose it over LFP, which combined apply to an extreme minority. And this thread is supposed to be about alternator charging of batteries, not everything solar.

Let's please try to keep this thread at least somewhat on topic. We're getting into the weeds here and it's not to the benefit of the gent who started this thread asking questions.

 

[RGFlinn]

Lots of internet experts have chipped in to confuse the OP and try to show their 'knowledge.' Many buses have larger alternators to operate their multiple lights and heaters. Check what your bus has installed. I suggest the OP look for things that operate on the 12v stored in your batteries. Converting from 12v DC to 120v AC inherently means a loss of energy in the inverter. 12v CPAP machines are available and certainly don't use 90w to operate! A little research also will find TVs and laptops that can operate on 12v, saving the losses inverting.

 

[HamSkoolie]

Lots of internet experts have chipped in to confuse the OP and try to show their 'knowledge.' Many buses have larger alternators to operate their multiple lights and heaters. Check what your bus has installed. I suggest the OP look for things that operate on the 12v stored in your batteries. Converting from 12v DC to 120v AC inherently means a loss of energy in the inverter. 12v CPAP machines are available and certainly don't use 90w to operate! A little research also will find TVs and laptops that can operate on 12v, saving the losses inverting.

HER CPAP running through a cheap inverter for the entire night wouldn't drain our batteries out of the green even on a three night trip with just 210AH (12 volts) with the genset running just long enough to make coffee in the morning and 5 or 10 minutes for the microwave.
The CPAP cord inverted the 110AC to DC so there's a double whammy there but it worked for us.
Long term, you wire a DC to DC cord for the CPAP and if needed include a transformer for the voltage your CPAP requires.

 

[flattracker]

Large capacity inverters draw more idle current than small capacity inverters. I agree that when little or no current draw occurs from an inverter then that idle current is low.



Since I will be working on the bus now, I will performing some idle current testing on both my inverters and will post the test results.



You can always use the large capacity inverter even with small loads, but I am using a small capacity inverter for my CPAP and fridge as it is more efficient. When power is applied from outside, generator, or large capacity inverter, the CPAP and fridge get their power from those sources instead.


Some buses have big alternators from the factory. I still advise keeping the bus electrics separate from RV electrics. Manufacturers size their electrical systems to support the intended use of vehicles. Their will be a certain amount of reserve in electrical capacity so that failures don't happen too often, but using that reserve could increase the chance of failure.

 

[HamSkoolie]

Yep separate chassis and house electrical systems though we will have a block heater (chassis system by my thought processes) fed off the house battery bank and inverter as well as the ability to charge the chassis batteries off the house via (the inverter and) a manually connected if needed battery charger.
When the factory AC compressors come off we're contemplating a second alternator, dedicated to charging but that won't happen until we've done some shake down time and see justification for the expense. It's an option we don't think we'll incorporate but it's an option.

 

[john61ct-SKO]

Minimize use of inverters, high efficiency DC native loads are better.

Buy multiple lower power, high quality inverters, better value and can turn each off when the device(s) being fed are not in use.

Redundancy, lower cost and less wasted power.

 

[Nawbdy]

Minimize use of inverters, high efficiency DC native loads are better.

Buy multiple lower power, high quality inverters, better value and can turn each off when the device(s) being fed are not in use.

Redundancy, lower cost and less wasted power.

So 3-1000 watt inverters instead of 1-3000 watt inverter. Would each be dedicated to a circuit or circuits or could they feed a common box and be turned on or off at need? Is this approach documented in one of the web based resources?

Assuming I move forward with my build this approach would work for me as I see myself adding loads across time as I make more decisions about what I want in my bus.

 

[HamSkoolie]

While redundancy is good, using multiple small inverters will use more power than a single larger inverter unless you buy a far larger inverter than needed. Duplication of basic circuitry will waste power compared to a single larger inverter. Smaller and cheaper inverters are less efficient and generally of lower quality as well.
The goal should be to properly size your inverter to your well researched and calculated load (including losses from efficiency, voltage drop, etc.).
Now the case can be made for more than one inverter if say you have nothing 110 running during winter months and run two air conditioners in the summer. That could be a case for an inverter capable of running the fridge and then switching on the big boy with you need those two air conditioners.
HOWEVER, this doesn't give redundancy as you'd have two wholly different inverters powering different circuits.


Far better to have a QUALITY (i.e. spend some money) inverter with sufficient size to handle your normal loads as well as PEAK loads. The Victron multiplus we will be installing has a 3000W continuous and 6000W peak (for 30 mins) rating. That will cover all of our 110 loads and even in a "worst case" scenario of the microwave and induction cooktop both on (2600W) AND both air conditioners (1600W) start, we'll be fine because that's only 4200W and the microwave won't be running for 30 minutes.
With the electrical system designed to allow a smaller inverter to be swapped in (at the loss of all the other capabilities of the multiplus), a cheap 3000W inverter can be carried (or acquired locally) should an issue occur with the nearly bullet proof Victron/GrowWatt/etc.
Redundancy is nice, simplicity and working autonomously in the background is probably far more important because.....we're humans, we forget, and those multiple wasteful inverters will often be left on, they create multiple failure points, and increase system complexity..... You should have a breaker panel for every inverter unless you're going to use 110 outlets physically on the inverter.


People attack problems differently. Having been in the mechanical trades for decades, I much prefer a robust but simple and easily repaired system unless I'm under the water, up in the air, or it's a life critical system.

 

[john61ct-SKO]

I did start off advocating eliminating AC devices as much as possible.

And turning off inverters whenever possible.

Selecting a small and cheap inverter to match a given (necessary) appliance that is only run intermittently, makes that work very well.

If one is a bit larger and services more devices that are left on for longer periods, that's OK too, but it takes more discipline to remember to power it down.

IMO off grid refrigeration should be DC native.

And aircon (if you must) should run off the genset, ideally recharging the House bank same time.

 

[HamSkoolie]

IMO off grid refrigeration should be DC native.

And aircon (if you must) should run off the genset, ideally recharging the House bank same time.

You OBVIOUSLY have never been within 1000 feet of my other half. LOL


THERE WILL BE 24/7 AIR CON.... PERIOD..... or forget about a bus, RV, motorhome.

That was the number one criteria and the reason for the size and expense of our electrical system.
$$4,000 Batteries
$1,300 Multiplus inverter/charger
$650 Solar charge controllers
$700 Solar panels (We found them used for an awesome price)

$1,000 Solar panel/roof covering rack


Plus all the wire, fuse and circuit breaker panels, main fuses, cut off switches, shunts, etc. Probably about $10,000 of our build will be JUST the electrical system


The fridge being a 110 unit is my call due to their efficiency, ease of replacement, speed of replacement, and refusal to submit to insane prices for an "RV" fridge. It's not the voltage, it's the other stuff.

 

[KeyWestPirate]

You OBVIOUSLY have never been within 1000 feet of my other half. LOL


THERE WILL BE 24/7 AIR CON.... PERIOD..... or forget about a bus, RV, motorhome.

That was the number one criteria and the reason for the size and expense of our electrical system.
$$4,000 Batteries
$1,300 Multiplus inverter/charger
$650 Solar charge controllers
$700 Solar panels (We found them used for an awesome price)

$1,000 Solar panel/roof covering rack


Plus all the wire, fuse and circuit breaker panels, main fuses, cut off switches, shunts, etc. Probably about $10,000 of our build will be JUST the electrical system


The fridge being a 110 unit is my call due to their efficiency, ease of replacement, speed of replacement, and refusal to submit to insane prices for an "RV" fridge. It's not the voltage, it's the other stuff.

I hear you. You are on the right track. If you do it half assed you will never be satisfied and a rework is always more expensive then doing it right the first time.


That given,, there are often budget constraints, and you can go overboard. My first inverter for my Nicaragua was a "big iron" unit, strong as an ox at 6000/12000. Nothing stops it. However, it sucks 240 watts/hour just turned on. We used it mostly for welding, the planer, then turn it off.



We experimented with 2500, 3500, and finally settled on a 5000 pure sine wave from a Chinese vendor. They all took the same 25 watts/hour on standby. That is about as good as it gets. We leave it on 24/7



I'm also struggling with the fridge issue. I've had a couple of gas refrigerators, both Dometic, and they work. There is nothing moving the air in the inside, so it stratifies. You can buy a small battery fan that moves it around.



We will have a cooktop, so propane. We will have an on demand water, we use that in Nicaragua,, works great as long as you size it correctly and have adequate water pressure. So propane.



The obvious choice is then a propane fridge, but I don't like them. They are silent, they do work, we had one that kept ice cream frozen hard in Mexico when it was 120 outside. They are designed to be built in. A plus, but also a minus. They have to be vented, and the flame has to be protected.



Other propane considerations: If you go with a fixed tank, like a forklift, you have to bring the bus to your refill point. Price and access becomes a bit of a problem, but RV outlets often sell propane and you can dump your holding tank at the same time.


I briefly considered CNG, it's commonly available in metro areas. It's selling for $3.75 /Gal in Tucson, but that includes road taxes. At the 3600 PSI we use on the buses, a tank would last a long time. But you'd have to buy a bus just to scrap it for the necessary parts -- and re-invent the wheel to get it all to work.



A small inverter generator from Harbor Freight to take up the slack ? Very quiet, run at load necessity, rather than at a fixed speed. A 2000/1600 and a 3500/3000 unit are available. The smaller one would easily run one mini split and put a bit of charge into the batteries. And it's quiet.



Your solar will provide most of your power, if not all, and shade the top of the bus. But, as someone pointed out,, if you are parked in the pines on some idyllic mountain,, you won't get from the solar what you are hoping for.


Could a mini split condensor be mounted horizontally on the top of the bus ? ? they are tall, but not very wide. Two condensors, two evaporators, one in the front, one in the back. That is what our new BlueBird buses do. The Thomas buses have evaporators running the length of the bus, above the windows, both sides. I'm talking evaporator location here. Before someone mentions, I could go with one condenser and multiple evaporators, the 12K BTU mini split is a commodity unit available in a complete kit for less than $600. Once you start to move in different directions,, the prices go up dramatically. Plus,, you have the redundancy of two independent units.




The post rambles, but the point: Go as big on the solar as you have roof and budget for. Sure,, some alternator tie in would be nice, since you are running the engine anyway. But,, going down the road, your solar panels will have full sunlight.


Size your inverter a bit bigger. To go from 3500 to 5000 watts is not that much more money.


Batteries: If you can afford lithium,, go for it. With depth of discharge, life, weight, maintenance requirements, they can't be beat.

Bargains are available in used batteries,, but you have to choose wisely.


https://batteryhookup.com/products/super-beast-module-with-48-headway-38120-hp-3-2v-8ah-24v






Thanks for sharing your ideas and designs. A bus is clearly a different beast than a stationary solar installation, and presents its own opportunities and challenges.