In search of a battery protector

[itsmoked]

We have gone thru,(destroyed), several battery banks that were being used for lighting by having them seriously over discharged.

We installed some battery minders which have failed miserably, twice!


Got any ideas on an alternative? 24VDC <100A

Keith Cress
kcress -

http://www.flaminsystems.com

 

[MacGyverS2000]

I'm imagining a simple zener/resistor series combo controlling the gate of a FET... dirt cheap, doesn't need to be exact on the cutoff voltage, etc. Once the voltage drops below a certain point, <POOF>, FET disables the connection... it reestablishes itself once a higher voltage is reapplied.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[DanEE]

Are you drawing power from the battery at the same time the charger is on it?

If so, some chargers "lock up" in absorption mode due to sensing the external load current and thinking that the battery is not fully charged and accordingly, proceeds to cook the battery..

Here is a little blurb about it..

http://www.ibexmfg.com/appnotes/app06.htm

If you do have external loads, you need a microprocessor controlled charger, or charger specificly designed to operate with external loads.. They will have the smarts to figure out the difference between external load and charging load drawn by the battery and respond accordingly..

Lastly are there temperature extremes involved with the batteries? If so, a temp compensated charger is necessary....

 

[cranky108]

For 24vdc you might look at some of the solar power stuff catalogs. There should be discharge protectors avertised there.
This is different from what DanEE is saying might be the problem.

 

[IRstuff]

The battery V vs. C characteristics should be known. Most battery minders tend to cut out too soon, at least in my experience.

Bear in mind that we're talking fractions of a volt. There may be something in the way the batteries are being discharged that interferes with the battery monitor. Are you pushing the capacity vs. discharge ratio? A high ESR might cause the battery monitor to still see a high voltage when the battery is already past the actual trip point.

TTFN

FAQ731-376

 

[itsmoked]

macgyvers2000; Kind of what I was thinking but more than I really wanted to get involved in this issue.

DanEE; No. If the charger was on then there would be no issue as it keeps up with the loads. Yes, I recognize issues with running a load off the bats while charging as I have designed several battery chargers and that IS a big hand waving mess...

No, in this case a rail car was left with a brainless clean up crew. They were told. "Do NOT turn off the generator, turn off all lights, lock the doors, and return the keys when you're done, I'm at the other end of the rail yard." After many hours a return to the car found the door propped open, the keys in the middle of the table, all the lights on, and the generator shut off and the battery minder mis-functioned.. Battery voltage was at 13V and the generator could not be restarted.

When shore power, (hence charging), was achieved several days later the batteries were fully sulfated with about 3% capacity remaining.

cranky108; I'll look in that direction.

IRstuff; Interesting point. I believe the bank was quite new and had a low ESR. I wonder if the lamebrain minder sees a low voltage, opens, sees a voltage rebound, closes, ad nauseum? I believe it opens once and needs to be reset. I'll check that. But even so, eventually it should disconnect still above cell damage voltage.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[IRstuff]

13 V out of 24 V sounds like an outright failure. Any way to verify functionality of the monitor independently?

A rather brute force alternative is to have an independent switching set that cuts out when the voltage drops below, say, 18V.

TTFN

FAQ731-376

 

[Madcow]

Google low voltage disconnect
They are basicly what MacGyver said.
Some have allot of features like high voltage trip and
ethernet warnings. Make shure its powered off the
charger/load side and not the batteries or it will
drain the batteries for you.

 

[DanEE]

Ditto on the low voltage disconnect..

There majority of the 48 DC Power Plants I worked on have low voltage disconnects..

Sounds like with the brainless operator factor, the LV disconnect is a must for your application..

 

[itsmoked]

Some of these look pretty good.
Some have absurd quiescent currents.

The one that has failed us is the ever popular Priority Start. I think I see why too. It disconnects the load at the low voltage point but then automatically reconnects if it sees a 2mV step function on the load side. Presumably by leaking current thru to the loads. This would be beneficial in making things brainless. Another words, when you return to the vehicle and a dome light is triggered the system re-closes automatically. Problem being that any noise source or corrosion noise or (?) can continouosly trigger re-closings clear down to the death of the batteries.

Some of these units I've found with your search criteria are straight hysteresis based switches no fancy restart stuff. Fully adjustable. I like it!

Thanks for the help.

Keith Cress
kcress -

http://www.flaminsystems.com