[Motorola] MTR-2000 Battery Revert Ideas

[Eric Lemmon]

Jay,

Yes, I have devised a simple and inexpensive means to accomplish the same
function as the Argus Technologies Battery Reverting Charger- at least for
the 40 watt repeater.

The large Anderson PowerPole connector on the rear of the 30- or 40-watt PA
is connected internally to the 12 VDC output of the power supply, and there
is an upstream blocking diode within the power supply.  Therefore, there is
no danger of damaging the power supply when the AC input fails while a
battery is connected directly to the PowerPole connector.

The MTR2000 has a software setting that can automatically lower the RF power
output when the unit is running on battery, and there is also a periodic
alarm beep that will let the repeater users know when the repeater is on
battery power.  The MTR2000 also will shut itself off when the battery
voltage drops to an adjustable setpoint.

Now, what I worry about is how to protect the power supply from being
overloaded when AC power returns, and the battery is now sucking up more
amps to recharge the battery than the PA needs for transmit power.  The
answer was simple: Use a relay with a 120 VAC coil to bypass a 2 ohm 50 watt
power resistor with its NC contacts.  When AC power is available to the
repeater, the relay is pulled in, and the 2 ohm resistor limits the amount
of current that is available to recharge the battery after an outage.
Suppose the battery was discharged to 9 volts at the time power was
restored.  The power supply output jumps up to 14 VDC, but the 2 ohm
resistor limits the recharge current going to the battery to about 2.5
amperes.  If AC power fails, the relay's NC contacts close when the relay
drops out, bypassing the resistor and allowing battery current to feed the
PA and the 3.5 and 5 VDC regulators.

I have already tested this scheme on one of my MTR2000 repeaters, and it
works just as I've described.  I have not tested this scheme on my 100 watt
MTR2000, which operates at 28 VDC, because it is plugged into a critical
power buss.

73, Eric Lemmon WB6FLY


-----Original Message-----
From: motorola-bounces at mailman.qth.net
[mailto:motorola-bounces at mailman.qth.net] On Behalf Of Coote, Jay
Sent: Monday, December 11, 2006 4:12 PM
To: motorola at mailman.qth.net
Subject: [Motorola] MTR-2000 Battery Revert Ideas

I am looking for low-cost ways to add battery revert to an MTR-2000
(12Volt) repeater, other than the costly Motorola unit.
Anyone been there and done that?  What will work?

Thanks

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