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Thread: Bad Converter (me thinks)
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04-24-2019, 07:44 AM #21
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Here's a thought experiment.
If in the same scenario above I replace the converter with a 1000 amp converter what would happen?
China syndrome? The city would go dark?
Nope. Actually nothing would happen. The demand for current is still 80 amps which the converter will supply without needing the battery and if the battery is fully charged the converter will go into float mode. Otherwise it will charge the battery until it reaches 12.6 and then go into float mode.
Don't believe me?
Go to your local parts store and buy a single element 12v led and a small spool of 28ga wire. Hook the led to your 1000 cold cranking amp battery with that thin wire. What happens? The bulb lights and nothing goes up in smoke. But wait a minute you've got this tiny .01 amp led and a huge supply of amps why doesn't it burn out? Because the internal resistance of the led is in balance with the voltage and will only use as many amps as it needs.
Let's now say I go out and buy a 55 amp converter that puts out say 24v. What happens now? Well bad things. Lights will burn extra bright and then quickly burn out. Pretty much the same for all the other appliances because the voltage is exceeding the internal resistance of the appliances. This is what happens when you have a short because your simply eliminating the resistance.
Now why the CYA disclaimers then?
The expectation there is that you're upgrading the supply of amps because you intend to use them and that means you need to know what your doing and they don't want to be responsible.
So say with that 1000 amp converter I now go and replace all my 15 amp fuses with 30 amp fuses because I'm going to plug in many more appliances. Well now that potential demand for amps just increased from 105 amps to 210 amps and the panel will likely melt down.
By replacing the converter with a 75 amp unit and not adding circuits or upgrading fuses the demand for amps remains unchanged just where the supply is coming from.
In the original 80 amp load scenario the 25 amp additional load that was being supplied by the battery meant that a 100 ah battery would last 4 hours before being depleted. With a 75 amp converter the battery would only be supplying 5 amp and would last 20 hours before being depleted.
Hope this helps.Last edited by freebird; 04-24-2019 at 07:46 AM.
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04-24-2019, 11:01 AM #22
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Freebird,
A wet cell battery has a VERY LOW internal resistance. A heavily discharged battery will allow a typical converter to pump max rated current into it. So the DC wiring from the converter to the battery needs properly sized to be able to handle converter max rated current. If the wiring is is undersized the wiring will get hot when producing max current.Jerry & Linda
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04-24-2019, 11:23 AM #23
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That's a good point, Jerry. However, I believe there is a 50a self resetting breaker in the line between the converter and the battery. There is on my 315. If it does its job it should limit overcurrent on the #6 wiring. If I were going with a converter capable of 80a I would size the wire and breaker accordingly. In this case #4 should do it allowing for up to 10% voltage drop.
BTW OP, I hope you were using the idea of upsizing fuses to get more capacity was for illustration purposes only. Fusing is determined by wire ampacity, not load.Last edited by Chiefblueman; 04-24-2019 at 11:26 AM.
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04-24-2019, 11:38 AM #24
GDRV typically wires the battery/converter/fuse panel with 6 ga wire.
With reference to the attached chart, the typical wire lengths barely meet the limitations for 3% voltage drop at 50A in 15 ft of wire. (Remember that circuit length is "there and back", not just the distance between devices) If you have a single battery (the OE configuration) all will probably be fine. If you add a second battery and still have the OE converter . . . things will still be fine. If you then upgrade the converter . . . you should upsize the wiring as well. (In my opinion)
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04-24-2019, 12:10 PM #25
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04-24-2019, 02:51 PM #26
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I used to have that memorizes in electronics class, but I have slept since then
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04-24-2019, 03:29 PM #27
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04-25-2019, 07:31 AM #28
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04-26-2019, 03:59 PM #29
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04-26-2019, 04:20 PM #30
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- Gene
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