Charging from alternator

[Bertnids]

This is where I'm getting really confused. There are diode isolators and continuous duty solenoids and VSR and solar charger with dc to dc charger combos. My brain is fried trying to puzzle this all out.

What do you use?
What are the pros and cons of different types?

 

[MikeRuth]

I'll give you one senario
I use 2 Trojan T-105 golf cart batteries in series for a total of 12 volts and about 110 amps usable.
I have two 120Watt panels on the roof going into a Tri Star 45 solar charger that feeds the batteries.
I also have the batteries connected  directly to the alternator through a Continuous duty solenoid that I can switch on and off from the cab.
And lastly I have a portable 20 amp Automotive charger that can be connected to 110VAC power to charge them when stationary if needed or to top off when the sun is not around.

I have currently a 2000 Watt Harbor freight Modified sign wave inverter to provide 110VAC in the van, runs my refrigerator and microwave.
Of course it can be used for other 110VAC appliances and gadgets. I would prefer to have a Pure sign waver inverter and will when I can afford it.
There are some electronics that donot like MSW inverters, for me I haven't found any yet so I'm good, with the exception of the microwave, it is not as efficient on MSW. but works.

OK so with that said, If I'm on the road my fridge is on and I use the MW to cook quick meals usually less than 5 to 10 minutes max. Even then that's a tough draw on those batteries so I usually support the batteries by running the engine at a high idle(1500rpm) and engaging the solenoid, that way the alternator is assisting with that high current draw. I do the same if I run any other high current item off the inverter.

On a normal sunny day I usually do not need assistance from the alternator, the solar does the job of keeping the batteries up.
Now on a cloudy day or rainy day or any other situation where the solar is not getting enough sun and I see my voltage dropping I'll engage the solenoid and let the engine supply charge current. I usually try to make sure as the days sun goes down that the voltage is up before I settle in for the night. Best I can

If I'm stationary and have access to 110VAC then I'll connect the battery charger and let that maintain them. If not then hopefully next days sun is sufficient and if needed I'll switch on the alternator when I hit the road. The alternator is NOT sufficient to charge the batteries completely unless maybe you are on the road for hours and even them most likely not. But it's better than nothing.

being a bit of a cheap skate I use a $89.00 Bar fridge from Wall mart that is 110VAC but it works very well and draws about 3 amps during normal run time. Not sure what the start up current is but I can tell you that both a 1500 watt or larger inverter runs them no problem.

Now you mentioned diode isolators etc. I'll let those who have gone down that road tell you about them, I preferred this route.
Really your going to be asked this question to get better answers, WHAT BATTERIES ARE YOU PLANNING ON USING?

The battery type will influence the best setup. 

Hope this helps a bit.

 

[MikeRuth]

I should also mention that Alternators were not designed for this setup, keep in mind that an alternators rating is for when the unit is at ambient air temp and as the alternator is pumping out juice it's getting hotter, and real fast when it's cranking out the max current. And the max current, say it's rated for 135 amps is going to drop rapidly as it gets hot, I believe many drop as much as 20%, bringing max down to say roughly 105 amps and maybe less, plus some of that current is going into keeping your vehicle running, I have done several test and with lights on, wipers on, blower on etc, see upwards of 60 amps going to just running the vehicle, and the standing voltage at that time may drop to as little as 13 volts or less. So your definitely not going to be charging the house batteries very well under those conditions.

A lot of folks don't realize that the starting battery is basically just that, it's to start the engine, once running the alternator is providing the current to run everything on the vehicle.

Ahh and one last thought, with a solenoid if your starting battery for some reason won't start the engine you can engage the solenoid and start the vehicle off the house batteries. This is a emergency option and of course you need to resolve the reason the starting battery failed.

 

[LoupGarou]

Different battery types require different charging profiles. If you’re going to mix battery types use a DC-to-DC battery charger.

 

[bullfrog]

In my first small set up where I drove at least 4 hours a day just hooking up a spare battery with a cable after I started the truck and disconnecting it when I stopped for the night worked fine. I also charged Ryobi batteries for lights and a fan while driving. As my power needs increased I went with solar and only used my alternator after several cloudy days. To prevent wear and tear on my alternator I eventually picked up a small generator that I seldom use but when I do I run out all fuel before storing. I now have enough solar I seldom need the extra charging but when I do I just stay someplace where I can charge batteries with a small grid powered charger and don't have to mess with a generator and maintenance or the noise. I imagine most people here end up with a solar system but you can get by with simple cheap cables, a manual switch, an extra battery and a reminder to turn the switch on and off in my opinion you are better off to save your money for solar.

 

[CC58]

The best way is a DC to DC charger such as Renogy 20A,40A,or 60A models for two reasons. First, if you have big bank of AGM that are highly discharged and directly tied to your alternator they can pull more current than alternator is rated for and burn it up. Second, a DC to DC charger has three stage charging which will actually charge batteries faster than a direct connection because it can boost voltage to 14.6V during the absorption stage while maintaining safe current levels.

 

[Trebor English]

Opinions are like orifices, we all have several. 

What I have is the best way.  I wanted cheapness.  My mini-van needed a new starter battery.  The best price I found was $100.  I got an $80 deep cycle trolling motor battery.  It was the biggest battery that would fit in the original location.  I have one battery so there is no isolator, no solenoid, no DC to DC charger.  My solar panel also keeps my starter battery charged even though cabin lights and AM FM radio sometimes get used. 

I have been warned that if I discharge the battery too much the engine won't start.  On the other hand, it is bad for a house battery to discharge it too much.  Does it make it good to deeply discharge one battery because you have another?  If it is bad for battery life, don't do that if you want cheapness.  In any case, I only have one battery life expiring at a time.  If reasonably treated batteries last 4 to 5 years i need one new one every 4 to 5 years.  With two batteries running it will be necessary to replace two every 4 to 5 years. 

Last month I had a problem.  A month prior I almost finished my gallon of distilled water and didn't  get another.  So last month I needed another gallon and the stores were out of distilled.  I used what I had and it was back in stock soon enough.  I'm not sure but I think I used two gallons since 2016.  Lead / antimony alloy deep cycle batteries really do need water.  It's 10 minutes per month. 

With the cheapitude of my setup I have no bragging rights. 

It depends on how much electricity you want to use.  This plan is good for small and cheap.  There will be no microwave, no electric heat or cooking, no air conditioner, no high power game computer.