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70 amp 12 volt power supply humming

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Austin the Ozone

Sat Sept 24 2011, 07:11PM

Registered Member #3989 Joined: Thu Jul 07 2011, 05:10PM
Location: In a van down by the river.
Posts: 52

Would you guys help me understand this? My battery charger is introducing a good bit of hum into my cb and am radio when plugged in. It also gets very warm to the touch after being in operation, however it says on the side panel that it draws 12 amps so getting warm while in operation might be normal. It has two small transformers and one large one and four diodes connected to a large heat sink. There are three filter caps in parallel that look similar to the type in a microwave oven. The voltage measures 14.5 volts dc but on the ac setting I get 36 volts- this because of all the ripple making my dvm read it as ac? I suspect I just need new filter capacitors as this supply was made in the early 1980s. I found the exact kind that are in it on ebay from italy but they are expensive. http://cgi.ebay.it/ws/eBayISAPI.dll?ViewItem&item=230537573051#ht_500wt_1156

So the question is, do you guys think the capacitors have dried up and are letting the hum through? Thank you, Austin

6178184993 6b1a794483

Austin the Ozone

Sat Sept 24 2011, 09:18PM

Registered Member #3989 Joined: Thu Jul 07 2011, 05:10PM
Location: In a van down by the river.
Posts: 52

I found some "motor run capacitors" that may work, is there any benefit to using more capacitance? They sell 12 mf caps I could just get that or three 4 mf ones for about the same price. http://www.grainger.com/Grainger/capacitors/motor-supplies/motors/ecatalog/N-9yp

Electra

Sat Sept 24 2011, 09:42PM

Registered Member #816 Joined: Sun Jun 03 2007, 07:29PM
Location:
Posts: 156

Most common battery chargers do not have any smoothing capacitors at all,
So they may be there for some other purpose like powerfactor correction, or the old type of magnetically regulated transformer (constant voltage transformer).

Or could have been just added by somebody else, the value of capacitance on the ones you were looking at looks far to low to be effective anyhow.

If you do add large capacitance to the output of a rectifier it will charge up to the peak of the half sine wave, (without a battery connected) so measure it before connecting your equipment.

If it were low current it would be simple to fit a voltage regulator as well, but for 12A itâ€™s not so trivial.
(edit) and even less so for 70A output.

Austin the Ozone

Sat Sept 24 2011, 10:42PM

Registered Member #3989 Joined: Thu Jul 07 2011, 05:10PM
Location: In a van down by the river.
Posts: 52

Electra wrote ...

Most common battery chargers do not have any smoothing capacitors at all,
So they may be there for some other purpose like powerfactor correction, or the old type of magnetically regulated transformer (constant voltage transformer).

Or could have been just added by somebody else, the value of capacitance on the ones you were looking at looks far to low to be effective anyhow.

If you do add large capacitance to the output of a rectifier it will charge up to the peak of the half sine wave, (without a battery connected) so measure it before connecting your equipment.

If it were low current it would be simple to fit a voltage regulator as well, but for 12A itâ€™s not so trivial.

Thanks for the reply, I found a manual for this charger. Triad-Utrac 570http://www.bdub.net/manuals/triad-utrad.pdf From reading it I gather that it is a constant voltage type. I don't understand the function of the capacitors or the effect there age is having on the supply. Caps can short out internally as well right?

I have read two different negative opinions on this type converter, http://www.tompatterson.com/AirstreamList/PriorMonths/2000_11/msg00519.html

http://www.travelkb.com/Uwe/Forum.aspx/rv/9316/TRIAD-UTRAD-Converter

Electra

Sun Sept 25 2011, 12:27AM

Registered Member #816 Joined: Sun Jun 03 2007, 07:29PM
Location:
Posts: 156

Yes most likely what the capacitors are for then, Iâ€™m a bit sketchy on the theory but basically these capacitors form a resonant circuit with an additional winding on the transformer core and its inductance, then magnetic shunts are used to limit the maximum current. The transformer is designed to work just where is saturates so the output voltage doesnâ€™t increase much further, so is less dependant on the applied input voltage.
You will probably find a much better description somewhere online.

Not that this helps you much with your problem as they have nothing to do with filtering, I imagine this thing pushes so much current into a battery that it causes a few volts of ripple across the battery voltage.

You could always try a filter between the battery and your radio equipment. Or just get an electronic power supply thatâ€™s better smoothed and regulated.

Nah

Sun Sept 25 2011, 02:51AM

Registered Member #3567 Joined: Mon Jan 03 2011, 10:49PM
Location: USA, 1960s
Posts: 260

i belive that these devices only have good regulation when under almost full load

Austin the Ozone

Mon Sept 26 2011, 04:56PM

Registered Member #3989 Joined: Thu Jul 07 2011, 05:10PM
Location: In a van down by the river.
Posts: 52

Thanks for the replies. Does anyone know or have a good guess what effect a faulty capacitor would have? It seems like it runs too hot, would changing the 30 year old capacitors maybe help it run cooler?

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