OpenBCM V1.08 (Linux)

Packet Radio Mailbox



 Login: GUEST

G8MNY  > TECHNI   06.10.21 11:00l 88 Lines 4588 Bytes #999 (0) @ WW
BID : 48768_GB7CIP
Subj: Regulating 12V Generator O/P
Sent: 211006/0847Z @:GB7CIP.#32.GBR.EURO #:48768 [Caterham Surrey GBR]

By G8MNY                                        (Updated Jun 06)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

Small generators often provide unregulated charging outputs. These can easily
over charge your /P battery, with damaging excessive battery voltage, that can
also damage low power lamps & other kit.

Here is s simple & efficient charge limiting SCR regulator that can be put in
the lead at the battery end.

1/ Charge output gradually shut of at 14V (dependent on Zener voltage).
2/ Low loss (1V) as it is an SCR & not a linear regulator.
3/ Generator connected LED, this lights when DC appears from the generator.
4/ Charged LED, gradually lights up as the battery takes less genny output.
5/ Battery lead isolation, no battery DC to short out @ the generator lead end.
6/ No battery drain, the circuit takes no current from the battery.

                              CHARGED ||
                                     + 100u              
               OVER                ĴĴ            470
              CURRENT                            10A     
               TRIP      +  LONG   2k2     SCR\          Fuse
Ĵ>o--o<<Ĵ >>o-o>loads
     RAW DC     GENNY     THICK     __GEN   270   /\g  CROCK 
   )<<Ŀ =\_/ ON    Ĵ>        + 
            CONNECTOR -  LEAD       LED     1N4001          12V
20V20V                                    __                 
(((((()Ĵ>                               /_\'14.5V           - BATTERY
 =======                             1k         Zener      CLIPS 
ALTERNATOR                         >>>
                                        SCR mounted on heatsink

The raw DC peaking well over 20V off load, lights the GEN ON LED via the 1k to
the -ve. The 20V also provides up to 14.5V across the zener. This puts 14V onto
the gate of the SCR via a 270R & blocking diode. If the battery voltage is much
less than this, the SCR will be triggered & puts nearly all of that 1/2 cycle
of generator DC into the battery. When that half cycle of current stops the SCR
is ready for the next voltage comparison & trigging for subsequent half cycles.

As the battery charges up the voltage rises & the SCR is triggered later &
later, in fact a crude form of phase firing naturally occurs, as the battery
voltage falls from the last current burst as the zener voltage rises..

                              14VĴ    _..--.   --..._.--...___
                              13VĴ  .'      '\              BATTERY VOLTAGE
25V_      _         _         12V_/ FLAT 11V   CHARGED 14V
       /' `\     /' `\
14VĴ  |     |   |     |      14VĴ   .--.     .--.
                              /'       `\ /'       `\  ZENER VOLTAGE
 0V_V_________V_________V     0V_V___________V___________V
       OFF LOAD GENNY DC     TRIGGER | early          | late

This does what you need for charging, it turns the current down as the voltage
comes up & stops excessive gassing. Eventually just the odd trigger occurs
keeping the voltage @ 14V.

If the charge current is small (small genny e.g. 8A max), & the battery a big
one with low internal resistance, then the hum across the battery may be small
enough not to cause hum problems at all with kit like a 22 Amp 100W SSB rig.

Using the low voltage output, means thick short leads! This does not help the
noise isolation problem. If you are closing doors on this lead, do make sure it
is not crushed! If you are using long leads due to noise, then make sure that
are VERY THICK. e.g. A 30A cooker lead with the 3rd earth wire bonded to -ve up
to say 10m long for an 8A charge lead, if the losses are not to be too great.

Some generators warn you not to use both DC & AC outputs at the same time. This
may not be due to loading, or regulation problems, but due to safety! This is
because the DC output winding is often part of the 230V AC load winding, & that
can put DC onto the AC output or bypass some of the safety trip features, as
well as MAKING THE 230V NON FLOATING & therefore more hazardous!

If you intend to use both at once do at least use a ELCB/RDC mains trip plug!

Why Don't U send an interesting bul?

73 de John G8MNY @ GB7CIP

Read previous mail | Read next mail

 22.10.2021 01:35:54lGo back Go up