93 Bigfoot 17CB - Magnetek Converter BAD! - Page 2 - Fiberglass RV

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Old 08-23-2007, 06:40 AM   #15
Trailer: Bigfoot 20 ft 5th Wheel
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Great link Michael, thanks very much! It's quite different from my set up but I'm sure the basic idea is the same and it will be a big help.

Now..if I ever get my trailer back from the kid..I can get started on it.

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Old 08-23-2007, 09:15 AM   #16
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This link shows step-by step several Magnetek replacements.

Best Converters

I've bought two Progressive Dynamics converters from Best Converters, good service and prices.

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Old 08-24-2007, 07:08 PM   #17
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I don't believe the batteries are self-limiting in any way -- I was at an auto parts place, having my rig checked after changing out my alternator (but not my voltage regulator; if the voltage regulator is not integral it's a really, really good idea to change out both alternator and VR at the same time, because one may have made the other bad in the first place!). The tech did something with the system to measure full alternator amps and, with the defective VR, the battery immediately started boiling over like I had never seen.... Clearly, my flooded lead-acid battery was not self-limiting.
I've thought this over and decided that the limiting factor is the voltage, not the current. As long as the charge voltage is higher than the battery voltage, current will flow and how much flows is based on the voltage difference.

Stumbled across a table on another group suggesting wire sizes (Take expected current and expected wire length to get wire size) for monster automotive sound systems (aka thumpers) but I don't know the underlying voltage drop assumption in the table. Here's the audio source and here's more copper wire info.
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Old 08-24-2007, 08:05 PM   #18
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Name: Michael
Trailer: 1993 Bigfoot 17 ftCB / 2011 Toyota Sienna
Posts: 195
Peter, et al;
There IS a limiting factor in the current drawn in charging a battery, and how much it can supply also.
Basically, the current drawn by the battery will be a function of the difference between the charging voltage minus the existing battery voltage divided by the Internal Resistance of the battery - excluding voltage drops in the cables, as you mentioned.
When new, an SLA battery has a lower Internal Resistance and this increases as the battery gets older and used up.
Internal Resistance of the battery is somewhat predictable by using a High Discharge Battery Tester!
I have a 100 Amp tester that, when discharging the battery for about 10 seconds at that amount, shows the Status of the battery as a function of Weak all the way to Good! What it is actually doing is measuring the voltage across the fixed resistance, a function of the Internal Resistance!
A regular size 24 Canadian Tire Marine Deep Cycle battery shouldn't give excessive current draw when charging in my application, but a depleted new AGM battery, with it's VERY LOW internal resistance would probably melt fuses and cables!

I just replaced mine and will keep an eye on it when charging after it's been depleted! As mentioned, I can use my Charge Wizard controller to drop the charge voltage to 13.6 or 13.2, if 14.4 gets too warm.

This advice and explanations are my own, after doing some research, and may NOT accurately reflect the total physics or reality of what does happen! Like ALL Internet advice, use your own judgement as to it's validity!

Now for some more camping!

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Old 08-24-2007, 08:18 PM   #19
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The reason I had the link and table above was that someone on another forum was popping 30A fuses when his truck was recharging his AGM house battery after a lot of discharge.

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