how hard would it be to use a relay to make a end of charge?

[nebriancent]

i have been reviewing various posts on using cc/cv psu as a charging solution
i have also been thinking of using a relay to trigger a disconnect from the power and perhaps light up a led

i was wondering if i could use a voltage divider eg a trim-pot to drive the base of a transistor with its collector hooked up to the psu output and its emitter hooked up to a latching relay so i can make a variable voltage latching relay and perhapse have a push button switch powered w/ a zenner to a second transistor to reset it

any cautions thoughts ideas or improvements (that i may be able to understand with my primitive knowledge) to this

i may be drafting up a rough schematic to kind of get my idea across if i get some time on the other computer

 

[nebriancent]

would something like this work??

 

[amberwolf]

Depending on the type of PSU you use for this, it may be much simpler than that. Some, like the Sorensons I have, have various control pin inputs on them that allow for external controls, such as thermal cutoffs, voltage cutoffs, etc. The manuals sometimes have application notes that give basic circuits to do various things with them, too.

On one of the Sorensons I have, it has an OVP (over voltage protection) that you could use for end-of-charge, I guess, by setting it to the point just at full-charge. Then turn the voltage of the Sorenson up to that point, so it shuts down. Mark the knob's point of rotation on the face of the unit. Turn it a smidgen down, then power it back on, and connect the pack. Then turn it back to the marked point. Once the voltage reaches that limit, it will shut the Sorenson off.

The thing I don't know is if the pack will then drain into the Sorenson's OVP circuits--that would rquire checking it's schematic to be sure this is already prvented by design, or providing a diode on the output of the Sorenson (and compensating for it's voltage drop) to keep the pack from backflowing into the Sorenson under any conditions.

I've never tried this on mine, but in theory it should work with any PSU that has adjustable voltage output and adjsutable OVP.

 

[Skippic]

I bought this:
Solid State Relay SSR-25 DA DC Output 24-380V AC 25A
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120725499234

It can easily be controlled by an IC.

 

[nebriancent]

I bought this:
Solid State Relay SSR-25 DA DC Output 24-380V AC 25A
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120725499234

It can easily be controlled by an IC.

i don't have much experience working w/ ic chips could you perhaps draw something up w/ a adjustable voltage tripping point and a suitable ic to work w/

im a bit of a cave man when it comes to this stuff .. im still about 30 years or more back in circuit design and understanding
but i figured the best place to start getting knowledge is the beginning and work my way up (still stuck in analog circuitry)

 

[Skippic]

For digital all you need to understand is the logic. With analog you need to know a lot more. Just get an adequate power supply and that's it.

 

[auraslip]

Your over thinking this! By the time charger voltage = pack voltage no current is flowing and the pack could be left on the PSU indefinitely. In fact terminating the charge as soon as it hits the charger voltage means you'll get an incomplete charge. For this reason chargers terminate when current drops to 1/10 C rather than using voltage.

Of course, setting charging voltage ABOVE what the final pack voltage should be means you'll be charging at CC the whole time which is quicker, and it can be set up so you'd get the same capacity as a cc/cv charge.

I just rigged up a cell-log's alarm port to shut off my battery discharger, and it works like a CHARM. Super simple too. Of course, for larger packs it may be impractical to have multiple cell logs.