The problem is very pronounced in solar off grid systems. Grid connected systems recover fast if the charger is properly sized.
From: Ken Hohhof Sent: Thursday, August 8, 2019 9:44 AM To: 'AnimalFarm Microwave Users Group' Subject: Re: [AFMUG] LVD That seems strange, I’m used to seeing the battery voltage jump above 12V as soon as the charger fires up. Maybe that’s what happens when you do a deep discharge, or when the charging current is fairly low? There are battery mgmt. systems that power the loads and charge the batteries separately once commercial power returns, I used to use a Trio model from Phoenix Contact that operates that way. I don’t like them though, because the load voltage would jump from regulated to raw battery voltage when it went on battery power. Closest to that now is the Traco BCMU which provides regulated power all the time, and doesn’t need the batteries to charge to the LVD upper trip point to resume powering the loads. But it has a very low battery charging current and isn’t really suitable for sites that draw a lot of power. From: AF <[email protected]> On Behalf Of [email protected] Sent: Thursday, August 8, 2019 9:59 AM To: 'AnimalFarm Microwave Users Group' <[email protected]> Subject: Re: [AFMUG] LVD My problem with LVDs over the years has been the hysterisis. Power has been back on for an hour but the voltage is still not high enough for the LVD to power everything back up. I never saw any difference in battery life in sites with LVD and non LVD. Generators are the way to go. From: Ken Hohhof Sent: Thursday, August 8, 2019 8:22 AM To: 'AnimalFarm Microwave Users Group' Subject: Re: [AFMUG] LVD Another approach if you can’t get out there fast enough with a portable generator would be strategic load shedding. Often we see that 90% of the customers are also without power so we’re getting no benefit by keeping the APs running, but maybe we’d like to keep the backhauls up so other sites aren’t affected. My observation is once you get to the LVD trip point, the rate at which the battery voltage is dropping has accelerated and there’s not much runtime left anyway. Also I worry about equipment getting into a locked up state if the DC voltage got too low but didn’t cleanly go off and back on. Normally we try to have enough battery runtime that we can get there with a generator. There are extreme circumstances though, like widespread power outages, or we’ve had ice storms that took down power wires but also made the roads impassable for 24 hours. I do sometimes wish battery management systems with built in LVDs would let us adjust the trip point a little lower, like maybe 19 or 20 volts instead of 21. From: AF <[email protected]> On Behalf Of Chuck McCown Sent: Thursday, August 8, 2019 8:57 AM To: AnimalFarm Microwave Users Group <[email protected]> Subject: Re: [AFMUG] LVD Philosophical question. With infrequent outages I would prefer to keep people on line for as long as possible, So no lvd or set it below where the equipment ceases to function. If you have protracted outages get a generator. I don’t see a use for lvd equipment unless it is in a remote area and powering non critical gear. Sent from my iPhone On Aug 8, 2019, at 1:12 AM, [email protected] <[email protected]> wrote: At what point would you want to enable an LVD on a 12V and 24V system? -- AF mailing list [email protected] http://af.afmug.com/mailman/listinfo/af_af.afmug.com -------------------------------------------------------------------------------- -- AF mailing list [email protected] http://af.afmug.com/mailman/listinfo/af_af.afmug.com -------------------------------------------------------------------------------- -- AF mailing list [email protected] http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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