charging batteries with a car alternator.

[tigger24]

Thanks Willy T, that is the easiest way I have heard of working the battery state and how to manage the charge system. Thanks for your help.

[Willy T]

Sealed batteries are really tough to keep up with. If you say these batteries are new and you commission them with a charge that the absorb current drops to say 1 - 2 % of capacity and you make that your foot in the sand and you return to that point each and every time they receive a full charge that's about the best you can do. You do not have to do a full charge every cycle you can go to to 85% for 7 days, + / - a day or two. Your depth of discharge ( dod ) should not be below 50 % or around 12 -12.1V .

There are sealed batteries that can be equalized, they are special batteries and it's just a couple manufacturers.

Most Batteries in the range posted ( 115 amp hr ) are Automotive / Multi Purpose will not have a long life in off grid use when heavily cycled.

[tigger24]

Ok that sounds like Iam on the right train of thought then. I just didnt want to replace the diesel genny if I could find a cheaper way to do charge during the winter, or at least until I have finished building my house and can spare some pennies !! I am new to this off grid living, thou totally loving it, and get confused with battery usage. Iam currently using toy stuff ( 12v) but will be replacing system latter for a more manly system. However by using 12v I can buy inverters (2000w) for £100, which runs prity much all I use, the batteries are 115ah sealed FLA x 10 @ £ 56 each. While using 1500w of pv via a Morning star 60 mppt £339, this during this time of year means that I dont need a top up with any other form ( gen ) But after talking to you guys, I am worried that I might have been using to much from the batteries and will be killing them. The only way of checking the % of battery for me is to look at the LEDs on the mppt. Could I use a standard 1000 amp meter to monitor the state of them so as that they might see next year. The mppt has on 1 or 2 occasions has shown the red LED which means that the battery is less then 30% guessing not good! A bit off track sorry but you have all been kind to me so far Thanks

[Willy T]

Thanks Willy T, looked up the price of this charger, quite high but will do the job. You say about your unit, how do you use yours, is it as a back up to pv or to boost during the winter?

It depends, You can use for either when there is a shortfall or on a as needed basis. It's not any different any other voltage controller. Basically this type charging is used in the rv / marine world for engine alternator output. Balmar also has controllers for their high output alternators.

As long as your in the Bulk stage below gassing ( battery voltage below 13.9v, 85 % soc ) you really are wasting your time with a controller, as they are not necessary. Once above gassing you then are beginning to head to the absorb trigger voltage that needs to be controlled. WWW gave you the most popular advise is to put in Bulk current and then let your solar finish the charge.

[lkruper]

Here is a product that could be used for 3 stage charging from your alternator. They also have bigger models to 400 amps. Do a google search to find a USA retailer.

http://sterling-power.com/collections/alternator-to-battery-chargers/products/alternator-to-battery-chargers-up-to-130a

On the cheap, I use a old Xantrex c-35 controller to give me 3 stage with any fixed DC input >30 amps. They will give you adjustable Bulk and float voltage, but only have 1 hour fixed absorb.

I found it on Amazon: http://www.amazon.com/Pro-Alternator...g+power+AB1280

Great tip.

[tigger24]

Thanks Willy T, looked up the price of this charger, quite high but will do the job. You say about your unit, how do you use yours, is it as a back up to pv or to boost during the winter?

[Willy T]

Here is a product that could be used for 3 stage charging from your alternator. They also have bigger models to 400 amps. Do a google search to find a USA retailer.

http://sterling-power.com/collections/alternator-to-battery-chargers/products/alternator-to-battery-chargers-up-to-130a

On the cheap, I use a old Xantrex c-35 controller to give me 3 stage with any fixed DC input >30 amps. They will give you adjustable Bulk and float voltage, but only have 1 hour fixed absorb.

[tigger24]

Thanks Wy_White_Wolf, I have just checked my Nissan truck and that is putting out 14.32v, but as you say still short of FLA of 14.5v. However as sun is short in the winter here it would help out the mppt by using in the morning as you suggested.

[Wy_White_Wolf]

Car/truck alternators are regulated to 13.6~13.8 volts. Using one to charge you bank will only get it to about 80~85% charged. WQhile that may not sound good it will work. If I did this I'd charge them with this in the morning. That way you could use solar to absorb charge them for the rest of the day to bring them up to 100%.

WWW

[inetdog]

Thanks Inetdog, I could decrease the engine speed by changing the the pulley sizes which should limit the the engine strain ? I think my main problem might be controlling the charge to the battery by not having any stage control. I can use an amp meter for the out put from alternator, but how can I tell how full the battery's are. Is there an easy way to tell how full there are at anytime ie a meter of some kind. At the moment I can only use my Morningstar mppt for a rough guide.

Once you have it calibrated for the increase in terminal voltage with current, you can get a rough idea of SOC from the battery voltage.
Note that running the alternator at a constant regulated voltage, with current limiting to protect the battery during the low SOC part of the charge cycle gives you essentially a Float charge profile, which Sunking often recommends for FLA when three stage chargers are not doing the job for one reason or another.

But the only reliable gauge of SOC are SG of the electrolyte and the resting voltage of the battery (no charge or discharge for at least three hours before reading.)

[tigger24]

Thanks Inetdog, I could decrease the engine speed by changing the the pulley sizes which should limit the the engine strain ? I think my main problem might be controlling the charge to the battery by not having any stage control. I can use an amp meter for the out put from alternator, but how can I tell how full the battery's are. Is there an easy way to tell how full there are at anytime ie a meter of some kind. At the moment I can only use my Morningstar mppt for a rough guide.

[inetdog]

Thats really helpful, thanks for this. I will try to find the info for my batteries and try and work out the out put from the car alternator. But as far as using my diesel engine and a car alternator, it would seam possible but not as good as it could be.

Probably the biggest problem would be the wear and tear on the diesel engine running at very low power but high RPM, along with the relatively poor fuel economy.

[tigger24]

Thats really helpful, thanks for this. I will try to find the info for my batteries and try and work out the out put from the car alternator. But as far as using my diesel engine and a car alternator, it would seam possible but not as good as it could be.

[lkruper]

yes thats correct, I just want to be able to charge the batteries directly from the car alternator. The battery charger I use at the moment is 100amps with 3 stage charging. Dose the car alternator not have 3 stage charging, if not dose it have any way of telling the current required so as that not to over charge.

Car alternators do not have the same capability as smart chargers. They also probably don't have the same voltage. A smart charger will start with a bulk charge at a particular amperage until it is 80% and then switch to absorb which is a different setting and then to float which is designed to put only enough power into the battery to overcome what it would be losing.

The Odyssey battery manual has a good write-up on how they like their batteries to be charged, how to use a vehicle alternator and the cons of doing so. It says in part:

All ODYSSEY batteries can be quickly charged. Figure 7
on the next page shows their exceptional fast charge
characteristics at a constant 14.7V for three levels of inrush
current. These current levels are similar to the output
currents of modern automotive alternators. Table 6 and
Figure 7 show the capacity returned as a function of the
magnitude of the inrush3 current.

Standard internal combustion engine alternators with an
output voltage of 14.2V can also charge these batteries.
The inrush current does not need to be limited under
constant voltage charge. However, because the typical
alternator voltage is only 14.2V instead of 14.7V, the
charge times will be longer than those shown in Table 5.

However, to be safe you need to find the instructions for your particular battery or contact the manufacturer and also find out what your alternator puts out, under load. AGM batteries have a narrower tolerance for input voltage than do FLA batteries.

[tigger24]

yes thats correct, I just want to be able to charge the batteries directly from the car alternator. The battery charger I use at the moment is 100amps with 3 stage charging. Dose the car alternator not have 3 stage charging, if not dose it have any way of telling the current required so as that not to over charge.