UVLO Re-design

Hard to say if you are over thinking it. I am going to assume you have a micro. I don't know how an A2D would help without it. Have you given any thought of including the current in your UVLO design?

It sounds like an interesting project. Good luck.

ry.

it A/D input available that I could dedicate to monitoring the battery char ge and disconnect it via a FET switch, contactor, or whatever.

ct the battery in order to charge it.

terisis via the A/D values so the thing doesn't chatter/oscillate.

micro. I don't know how an A2D would help without it. Have you given any thought of including the current in your UVLO design?

Yes, an 8-bit micro. The charger is current limited to 5 amps @ 54.4 VDC, so I had not planned t o do anything further with it.

The micro is powered via several sources "diode-or'd" together. I guess I'm just wondering if the UVLO should be totally independent of the micro? I don't see much advantage in doing so, and I think it complicates things to go that way. I'm wondering if there's a reason NOT to implement a UVLO under micro control. (?)

Do both. Use the micro to do UVLO (and OV) under normal circumstances, allowing it to do a systematic shutdown. A hardware UVLO (usually part of my primary regulator) yanks the plug before smoke.

Why not use a micro and _really_ over-think it ?>:-}

What does "UVLO" really mean: Disconnect from load; shut down the load function gracefully; reset the digital; what? ...Jim Thompson

tery.

-bit A/D input available that I could dedicate to monitoring the battery ch arge and disconnect it via a FET switch, contactor, or whatever.

nect the battery in order to charge it.

ysterisis via the A/D values so the thing doesn't chatter/oscillate.

a micro. I don't know how an A2D would help without it. Have you given a ny thought of including the current in your UVLO design?

to do anything further with it.

he micro? I don't see much advantage in doing so, and I think it complicat es things to go that way. I'm wondering if there's a reason NOT to impleme nt a UVLO under micro control. (?)

I don't think I explained very well. The battery pack terminal voltage alo ng with the load current and temperature can be used to get a reasonable me asure of state of charge. You may want to include these inputs to the micr o. Write the code later down the road to improve the performance.

I am off-grid electric-wise and run a 48v bank of Die-hard deep cycle. I a m running 2.5kW chargers.I hope to do a 10kW charger this winter. I have 1

On Sunday, October 8, 2017 at 3:42:54 PM UTC-4, Jim Thompson wrote: ...

In this case, UVLO essentially means disconnecting the battery from the (lead acid) battery from the load so as not to drop the cell voltage so low the battery cannot recover with reasonable capacity.

Which brings up another problem I am having with the AHJ on this project. He wants an alarm at 20% battery capacity remaining and I'm not sure I care to discharge a typical lead-acid that far. (Not to mention, determining that 20% is a problem unto itself.)

I don't need the UVLO to "protect" any circuitry. That's already handled. I just don't want to completely discharge the battery.

I meant to type: "means disconnecting the lead acid) battery from the load..."

Maybe I shouldn't drink margaritas when I type? :)

A uP sounds ideal. As a bonus, you could look at the voltage across each cell.

Sure you should. I've gotten some of my best ideas while "relaxed" ;-)

Sometime thinking too hard obscures the trivial solution. ...Jim Thompson

Don't forget that discharge is a slow effect, and so is overdischarge protection. You must filter the voltage(s) to avoid triggering on brief voltage spikes due to load changes.

Regards, Allan

Also, wont one need to disconnect the load momentarily to sense the real element voltage, so the ESR is not in the equation?

Cheers

Klaus

No. A nearly "dead" battery, unloaded might read a decent voltage. ...Jim Thompson

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