charging batteries with a car alternator.

[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.

[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]

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]

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.