Charging multiple 12v batteries in parallel?

forgotmyname

I have various 12v batteries that range from small 4Ah 12v SLA to car type to larger leisure type in excess of 100Ah capacity.

Looking at connecting them to a charger / solar panels in a way where i can monitor them and charge them easier than having to get the multi-meter out each time to check each one.

Tinkering with arduino's and stepper motors and spotted some voltage monitoring addons for arduino.

I want each battery to be isolated for the power output though.

Can anyone suggest the best method? Simple diodes or something more power efficient?

Any suggestions?

were

yup, single diode for each battery, as it will stop reverse current should 1 battery fail, assuming your charger has automatic over current protection, all of the same voltage and cell construction type

Undervalued

were wrote: »

yup, single diode for each battery, as it will stop reverse current should 1 battery fail, assuming your charger has automatic over current protection, all of the same voltage and cell construction type

Yes but you will get a volt drop of about 0.7 of a volt across the diode so, depending on your charger, it may not ever reach full charge.

Some (not all) peak detection type chargers can be fooled by protection diodes so may not behave properly.

were

Undervalued wrote: »

Yes but you will get a volt drop of about 0.7 of a volt across the diode so, depending on your charger, it may not ever reach full charge.

Some (not all) peak detection type chargers can be fooled by protection diodes so may not behave properly.

yup, but only 0.3v for Schottky diodes. You could very well be right about the peak protection chargers, unsure about this, but think it could be bodged with a very high ohm resistor across the diode in parrallel (would take a stab at 220k - about 6 microamps@12v), so acting like leakage without having any real detrimental effects.

Reading the post again it looks like a relay set up too, because he has to disconnect the batteries to measure it, but measuring voltage alone is not a true value of the charge capacity in a battery.

forgotmyname

I could use a dumb charger or connect directly to each cell if one does drop considerably.

Mainly hoping solar panels will keep them topped up, which should put out about 17v i think, but fairly low amperage.

I was just wondering on using an arduino and battery monitors with bluetooth to report the voltages.

Will have to experiment on the current drain from them though.

These arduino's are addictive.

PS... Which diodes to use? What if the panels expand and i get 10amps going to the batteries? Will the diodes stand upto that?

Thanks

were

These are rated a 400 amps, but think since there are 2 diodes that it is 200A each
http://www.ebay.co.uk/itm/MBRP400100CT-400A-100V-SBD-Schottky-Barrier-Rectifier-Diode-Module-/121688296724?hash=item1c55300d14:g:6JcAAOSwuxFYuBd2

http://www.ebay.co.uk/itm/MBR20100CT-F-Dual-DIODE-Common-Cathode-SCHOTTKY-20A-10a-per-Diode-100V-x3pcs-/291793120260?hash=item43f039ac04:g:-tAAAOSwbYZXYVaM
http://www.ebay.co.uk/itm/MBRF1645-Diode-Schottky-rectifying-45V-16A-TO220-max3-16mm-/201600214470?hash=item2ef04f25c6:g:4EoAAOSwvg9XWIK7
http://www.ebay.co.uk/itm/10pcs-10SQ050-10A-50V-R-6-Schottky-Rectifiers-Diode-/121945292587?hash=item1c64817f2b:g:26oAAOSwHjNV~3yc
You could probably pull some out of old computer PSUs for free too

For silicon and something larger up to 50A at 800V
http://www.ebay.co.uk/itm/All-Rectifier-Bridge-Small-Signal-Rectifier-Diodes-1N4-KBU6-KBPC-GBPC-/200737932079?var=&hash=item2ebce9c32f:m:mFddpsjbnEnWIJwxv-Y_tJg

To be fair, you really should test the battery by isolating it, putting it on a suitable load and watch the voltage and current drain, like a decent battery tester does.

I would put a slow blow fuse on each battery too of say 10A, just to be safe. Be aware of voltage spikes, especially when contacts open and close.

forgotmyname

I have a selection of bridge rectifiers. Nothing over 4A i think?

No shortage of fuses etc.

How do you check whether a diode is a Schottky one? Just check the forward voltage is approx 0.3 and not 0.6 or 0.7?

were

on a multimeter, some tell you the forward voltage. old way is 9v battery and a 1k resistor and a diode in series, just use the volt meter and measure across the diode ends.

On cheaper meters with a diode test, the Schottky will have less of a resistance compared to silicon, and both will block reverse current as diodes do. Once you have done a few you get a ball park reading.

Also there is writing on them - usually, get that magnifying glass out:)