Thats right you want to check it before charging.
If you are going to switch the high side a P FET is probably the easiest way to go.
Here is a schematic for a high side switch.
Another thing to think about is the ripple on the battery voltage. How do you plan to terminate the charge?
Also note the short glitch at turn on. This is from discharging the filter cap in the logic supply. Might want to "work around" this in your software.
If you want to PM me your address I'll drop a couple of FETs in an envelope. I've got a tube of IRF4905's.
Ron
How does this look for output control?
Q2 will be a 2N7000 or similar, depending on what I have in stock. Maybe pull down resistor needed on pin 5? 1K value typical? I am thinking to prevent false triggers?
How does the rest of the cct look? See any glaring errors or poor practices? It seems to work, under test conditions, but wondering if you or anyone would have any suggestions?
I added a resistor to the controller output too, as seen in the schematic only.
Thanks
On your advice, I ordered up some irf4905's ....and some ndp6020's. If I understand correctly, the 6020's can be driven directly from a microcontroller ie full on at 5 volts (or zero in the p channel) and off at the opposite, yes?
With Digikey, I will have them tomorrow...pretty good service here in Canada with them.
Hey Twister, thanks for the input. The micro puts out what ever you need and in my case, I set the output full on (whether that be zero or Vcc level depends on what I am driving) for a full charge rate. When the micro detects a battery voltage=80% of what I consider a full charge (14.3ish for a 6 cell battery) then the output becomes a pulse train, with a 20% duty cycle, (pulse width modulation), reducing the charging rate and this continues till the battery voltage reaches the 100% level. Then the output goes full off but the micro will check the battery continuously or occasionally, depending on what I set, ie hourly,every minute or continuously, and should the voltage drop below the 14.3, then it will enable the charge rate at 20% again.
This is a very interesting project that you are building. I learned a lot from that battery university link. You now have the first two stages programed. The 14.3V would be the topping stage. I know that my batteries boil at 14V. You can remove the top of the battery to see if it is boiling. Be careful of sparks while you are charging at that voltage. The battery can explode! I guess it would be simple to add the third stage of a float charge if you wanted.
That is my theory, mostly from what I learned in this thread as to how the battery should be charged. I am relying on the original battery charger transformer and rectifiers and cct protection (a built in cct breaker) to limit the current. ie I am not controlling charge current nor monitoring it. I only say full on, 20% on and off. This is a retrofit to an old charger so I did not start from scratch to build a charger.
As to choosing the Nano8, I stumbled across Basic Micro line and the pricing on them looked reasonable. I am familiar with the old BASIC Stamp and have an old Atom stack around here but never really used it. I am hoping to move into Pic's directly one day but for now, I am happy with a $3 chip. The programming software is free and relatively easy to use. The guy who owns the company or at least who I corresponded with a few times seemed pretty good (helpful). I have used some of the larger Nano's too driving an LCD display and doing some experimenting and they seem to work well. I thought the Arduino series was much more expensive than I have found lately so I must have been looking at some the more powerful ones. I have noticed that there is not much chatter over on the https://www.basicmicro.com/ forum though. Nathan (owner) said he has sold a lot of chips so I guess that those buying them don't ask as many questions as me....;-) He is the one who answers my questions most of the time, although a couple of others chime in occasionally. They might have more discussions in the other sections.
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