High output alternator?

[blueridge]

Hello,

This seems like a good idea but I don't see anyone else writing about it in the archives.

Could you use a high output alternator to recharge your house batteries instead of using solar panels?

Link is to a HP Alternator replacement for an Express Van.  200amps 12v at idle.

I use 80-100 amps a day and generally drive some, most days.  

Looks like 30 minutes parked at idle (1/2 gallon), or some driving would keep me charged.

If I used a Genie smart charge controller to optimize my vehicle and house battery charging, would this work or am I missing something?

Why isn't this a more popular choice?

Thanks

 

[bullfrog]

Idling an engine is never good and anything that puts a load on it while at idle increases wear and decreases economy. A small inverter generator is much cheaper to use and replace than your vehicle's engine and it is engineered for the job. Most alternators do not start charging until they reach a higher engine speed. If you drive at higher speeds 4 hours a day normally and don't mind slightly lower fuel economy it probably works fine even though nothing is free it would be close.

 

[rokguy]

Add to that, the alternator while being run off an engine will always charge the engine vehicle battery first before it will start charging aux batteries as bullfrog states a long drive would usually be the only answer.

 

[highdesertranger]

"Could you use a high output alternator to recharge your house batteries instead of using solar panels?"

short answer, No

"200amps 12v at idle."

don't believe it, it's marketing hype. it might hold 200 amps for a very short time but not for more than a minute or 2. it's going to get very hot if you try to make it put out the max for a long period of time, you will burn it up. also your factory wire in no way can handle 200 amps.

driving some doesn't cut it. to recharge a deeply discharge battery takes 6-8 hours of driving at highway speeds. you will need to do this everyday. leaving a battery in a discharged state will severely shorten it's life.

now I am not saying don't use alternator charging but I am saying don't rely on it as your only charge source. I would use the largest OEM alternator that came with your vehicle and do the solar.

highdesertranger

 

[Oneleggedcowboy]

Interesting concepts.

 

[tx2sturgis]

The short answer is no...that wont work well. 

But here is the long version:

Your math and electronic terms are not quite on the mark....you dont use 80-100 amps a day. You probably mean you use 80-100 amp-hours per day.

Your alternator will help replace the energy used, but it takes a few hours to replace the energy that took you all day to use, because lead-acid batteries have a charge profile... you cant just dump in massive amounts of amperage in 20 or 30 minutes and magically replace the 50% SoC (state of charge)  you pulled. And as pointed out above, a high output alternator is a bit of a hype. There are reasons for this, the short version is: limitations at idle, limitations of your other components, and limitations of the chemical charge process in a typical lead-acid battery after being drained for many hours. 

If your house battery is rated at, lets say, 200 ah, and you pulled 100 ah, then that is about 50% SoC and it will take a few hours to replace that. Lead acid batteries rely on a slow chemical process to charge and discharge. No getting around that. So, with lead acid it cant be done in 20-30 minutes.

If you wish to invest in lifepo4 batteries (and the infrastructure they need to be able to do this) you CAN replace that amount of energy in a half hour...easily.

As mentioned above, solar panels and a generator, are a practical, affordable, effective way to do this.

 

[Zephyr]

I've considered building a poor boy battery charger using an 1988 Chevy alternator and a small 3 to 4 horsepower gas motor. GM alternators have the voltage regulator built in and charge at around 14 volts. That would charge and eventually top off a lead acid battery as solar does. But I'm now understanding that there's no amp regulator, so the alternator could be overloaded and toast it's wiring. Is there a way to limit the amp load?
Maybe spin it slow, maybe 1200 rpm?

 

[bullfrog]

A small motor has a hard time turning an alternator under full load. You would much better off just buying a used generator off craigslist. There are plenty out there.

 

[highdesertranger]

do homebuilt alternator generators work?

kinda but do you want to listen to that thing for 6+ hours.

highdesertranger

 

[tx2sturgis]

I like the idea of directly recharging batteries with a small portable engine powered alternator. You can DIY these or buy them already built. 

But as HDR points out, they are noisy, and until Honda or Yamaha makes one that's quiet, we are kinda stuck with normal inverter generators.

 

[Zephyr]

Do inverter generators charge batteries at 14 volts? If so, I'm trying to reinvent the wheel.

My reason for a DIY alternator battery charger is the 14 volt input to the battery. Seems like 12 volt input would take a lot longer to get the last 20% of recharging done. I have a fairly new, high output GM alternator in a parts 1988 Suburban. That's the reason I am considering this build. Found plans for a DIY rig. He put a fairly large industrial muffler on it and could hear the tappets click.

 

[highdesertranger]

with the inverter generator you run a battery charger. a Honda 2200i can handle a 60A smart charger. that's going to charge better and faster then any alternator based homebuilt system.

you are not comprehending how long it takes to fully charge a depleted battery back to 100%. no matter what source you use and how much it puts out it takes 6+ hours. do you want to listen to a generator for 6+ hours every single day? especially one using a lawn mower engine? plus all the gas. those are the reasons solar is so popular, no gas to buy, charges all day as long as it's sunny, it is silent.

one more thing most people who try to quite a loud generator down have no idea what they are doing. you cannot just add longer exhaust pipes and bigger mufflers. both of those is increasing the backpressure. any increase in backpressure has a detrimental effect on the engine power and HP output. to much backpressure will result in a short engine life.

unless you are rich and like to tinker, spend your money on solar you will be much happier. so will everyone camped anywhere close to you.

my 2 cents

highdesertranger

 

[Zephyr]

Thanks HDR, I appreciate your perseverance explaining why an car alternator is a bad solution. Yes, solar is outstanding, especially since it's getting more affordable. I will save my extra alternator for my '87 Chevy pickup.

 

[highdesertranger]

you have an 87 Chevy PU, now you are talking my language. the last year of the square body(1/2 and 3/4 ton). need any parts I have lots of parts? is it a 4x4? 1/2, 3/4, or 1 ton. highdesertranger

 

[rokguy]

I think the only fast charge alternator (besides Wind power) I know of is a tow behind the stern one, a lot of offshore yachts use.
On land the only way you could use one, would be if you were camped beside a fast flowing river/stream and use it like a Pelton wheel.
Even then it would take hours to complete a lead acid battery charge.

 

[Zephyr]

"you have an 87 Chevy PU, now you are talking my language. the last year of the square body(1/2 and 3/4 ton). need any parts I have lots of parts? is it a 4x4? 1/2, 3/4, or 1 ton." highdesertranger

It's half ton, four wheel drive, auto with a 305. It's in decent condition, a little rust but overall the body is in good condition. It comes from an era when pickups were work trucks. If I need anything, I'll PM you.

 

[Ticklebellly]

Could you use a high output alternator to recharge your house batteries instead of using solar panels?

200amps 12v at idle.

Looks like 30 minutes parked at idle (1/2 gallon), or some driving would keep me charged.

Why isn't this a more popular choice?

Answer to the first question is Yes.   Lots of people do it but usually have a combination of Alternator and solar, for efficiency.   One or the other is possible but Alternator while moving and Solar while stationary is more flexible.   Alternator and Solar to a dual input DC to DC charger is the most successful combination.

200 Amps at idle is about capability not what you get as output at idle.   Alternators supply to demand, they are not constant current devices.

30 minutes at idle is just fantasy.   That's why it is not a popular choice.   Alternators supply current as a function of demand.   An alternator putting out 14.1 volts to a battery with a terminal voltage of 12 volts might supply quite a few amps, but as soon as a surface charge is established, the current will drop to not much.   Alternator charging only of a well depleted battery might need more than 12-14 hours to charge that battery.   That's why is is not a popular choice.

 

[LoupGarou]

Yes, but it’s more like 50 to 60 amps at idle. Some vehicles have a PTO off the transmission and are designed to idle at length.

Goal Zero has nailed it.

 

[Gr8ful]

I have a deisel ambulance with a 250 amp alt that charges the 2 engine batteries 1st the a switch charges the house batteries. If you set the parking brake while running it increases the rpm to about double the idle but I seldom do that but better on the engine than idling. I also have a very quiet small genset & charger. It all depends on if there's sun where you are & if you mount solar to rge vehicle do you want to park in the sun? Also how much power you use, how much you drive, etc. Lots of variables & no perfect answer without knowing these things. Good luck!

 

[blueridge]

Thanks for your insights,

So first the disclaimer, I don't know much about energy production and control, so I was asking here because there are people on this forum who have a lot of knowledge and experience to draw on.

I have read some interesting (and different) ideas about charging house batteries.

High Cost (leading the way?):   

The higher end RVs (like Advanced RV conversions) have stopped using solar panels all together and are using high powered alternators to re-charge their house batteries.  

The Advanced RV  installations use a smart controller that first recharges the van's starter battery in a few minutes, then diverts the alternator output to your house batteries and ramps up the output of your (upgraded high capacity) alternator to quickly recharge your house batteries to 80%, then gradually reduces the alternator output to prevent overheating your house batteries as they approach the final charge to 95%+

Low cost version:

I've read of other people who are doing this in a low cost way.  They are using low cost used AGM batteries (400-500Ah bank) and are recharging them with a high capacity alternator, and a separate (traditional) voltage regulator attached to their house batteries.

They switch between recharging their starter battery and their house batteries, manually  - and have decided not to add any solar because this was working without them.  But, this doesn't seem to be a common practice, and I wondered why.

I do a fair amount of driving each week, and rarely boon-dock in one spot for an extended period of time.   I wondered if this would work for me, so I asked here.

I fair number of people here have suggested this isn't a good idea ... and I posted to get the opinions of people who have more knowledge in this area.