Solar Battery Charging and Diodes

You might try using a schottky diode instead of a silicon diode. Schottky can have a forward voltage drops as low as 0.3 volts. This might be low enought to make a big difference.

Alternately you might check to see your charger has a tweakable output voltage and bump it up enough to overcome the diode voltage drop.

Dorian

Schottky diodes have a lower vf - but you still have a problem. The diodes and the fact that the batteries are simultaneously connected to the charger interfere with its "inteligence". It is expecting to "see" battery voltage of one battery - with no interveneing diode drop. Suppose you have two batteries connected to the charger through the diodes - one that is low enough to require charging at the bulk rate and the other that requires trickle charge. Your charger can't accomplish both simultaneously - its "intelligence" is negated by the configuration.

To use an intelligent charger's "intelligence" it needs to be connected to a single battery at a time. So you could add a cycle circuit - a 4017 counter driving relays for example - to connect one battery at a time to the charger. Build a 555 astable for something like ten minutes - precision is not needed - and pulse the counter with it. Set the counter for the number of batteries, N, by connecting output N+1 of the 4017 to the reset pin (15). The outputs from the 4017 will need to feed NPN relay drivers. You can get additionally "fancy", sensing the connected battery's voltage with a comparator, and speeding up the 555 if the comparator determines that the battery is at a trickle charge level.

Ed

What we ended up doing is put relays and current sensors between the batteries and the charging buss. A counter would sequence the relays and sense which battery was pulling a significant amount of charging current and it stopped counting at that point, when the current dropped it continued counting to test the next battery.

I had a feeling that might be the case....

Cool idea...a nice little project for me. Thanks heaps!

RJR

Relays are somewhat clunky aren't they? Sounds like a good idea though.

What did you think of ehsjr's cycle circuit idea?

RJR

Opps...I didn't catch his message. My news server might have been slow to pick up on it.

That pretty much what we did. But 30 years ago, when all ya had were 200 relays sitting on the shelf begging to be used for something... :)

cheap and efficient, good enough.

to use regular diodes with this you need to modify the charge regulator so it gives out 0.6 more volts. the details of how depend on the details of what you have.

if the regulator shares a common earth with the batteries it may just be a matter of inserting a diode in there as well.

before ______ _________ _______ | +|---|in out|---|+ | |P.V | | REG | | | | | | gnd | | 12V | | | `---+---' | BAT | | | | | | | -|-------+-------| | ~~~~~ ~~~~~~~ after .--------------+-----------..... ______ _________ | _______ | ______ | +|---|in out|-+->|--|+ | `->|--|+ | |P.V.| | REG | | | | | | | | gnd | | 12V | | 12V | | | `---+---' | BAT | | BAT | | | | | | | | | -|--. `->|-. .----| | .----| | ~~~~~ | | | ~~~~~~~ | ~~~~~~~ `---------+-+--------------+---------....

no, in that situation there will never be a way to charge the full battery until the flat one catches up.

Bye. Jasen

It sounde very similar to what he did.

Bye. Jasen

to help you along, they make latching relays !, this can reduce the draw on your system by not holding the relay down.

Hi,

Thanks, I think I understand. The controller/regulator is dipped in resin so I can't examine its circuit.

I'll do a continuity test to see if the -ve is common from the PV thru the controller.

RJR.

It gets even worse. If the thing works on voltage sensing vs current sensing (voltage sensing is probable), it can't "read" the battery voltage through the diodes. It may not charge at all, or, if it is not intelligent enough, may overcharge. If it is current sensing (doubtful), the diode drop interferes.

Ed

You can't use diodes with an intelligent charger. You have to connect the charger to the battery without an interveneing diode. With a diode between the charger and the battery, the charger has no means to sense the battery voltage.

The exception would be a charger that relies soley on sensing current drawn. I am unaware of such a charger topology, but even if it does exist, the diode would interfere with accuracy.

Ed

how about putting a capacitor across the charger output.

For what purpose? Do you think it will somehow overcome the problem caused by putting a diode between the charger and the battery??

Ed

yes.

what problem are you seeing, I note someone has trimed my schematic off, you may want to go and look at it, I don't think it's what you're expecting.

Bye. Jasen

"You can't use diodes with an intelligent charger. You have to connect the charger to the battery without an interveneing diode. With a diode between the charger and the battery, the charger has no means to sense the battery voltage."

The one you posted won't work properly - the "intelligence" is defeated by the diodes. If it was a constant voltage charger, it would be fine. The diode in the ground leg does *not* solve the problem when you use an intelligent charger.

Ed

I can't fault your reasoning Ed, there is none shown.

how about this one?

Bye. Jasen

Can't read, or don't understand? It's been repeadtedly stated: the intelligent charger cannot sense the battery voltage through the diode.

Ed