Converters - Fiberglass RV


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Old 04-22-2003, 09:09 AM   #1
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Converters

We've discussed batteries, solar panels, inverters, etc. Now I would like some information on converters.

If I'm going to replace my battery with one of those super duper jobs, then I might as well get a new converter -- hopefully, saving my new battery from a possible failed aging converter.

I would like to know what the primary differences are; what those differences are to a unlearned person, like me; and what, if anything, should be taken in account if I'm going to use an inverter.

Pretty much just general info. I know what they do and remember reading something about a feature that keeps it from overcharging. That's about my limit of knowledge. What is considered a good upgrade and why is that important?

Thanks
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Old 04-22-2003, 12:50 PM   #2
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clarification, please
inverter - inverts(converts) 12v to 110
converter - converts 110 to 12v

so if you plug in to 110 you need the converter to use the 12v system

so if you don't plug in to 110 you need the inverter to convert the battery to use the 110 equipment.

now - if this is true then if you only have 12 stuff you would only need a converter

or - if you only have 110 stuff you would only need an inverter if you use a battery and neither one if you plug in.

Is this all correct?????
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Old 04-22-2003, 04:14 PM   #3
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T & J

Yes, altho if you only have 12VDC appliances, you can run off the battery until it runs down and then recharge it with the truck.

The converter does essentially two things:

1. Provides 12VDC for appliances

2. Recharges the 12VDC battery.

Older converters don't do a good job of charging batteries because they don't have the smart charger technology to keep from overcharging the battery if left on for a long time, so you want a converter that has smart (3-stage; bulk, absorbtion and float) capabilities. That will cost a few bucks.

If you want to use Gel or AGM batteries instead of the more common flooded lead-acid batteries, the charger portion of any converter or charger must be capable of charging those batteries properly.

Each converter is different, depending on make, model and version. Get the numbers and call your manf to find out what yours will do if you have one.

Consider spending about $100 or less for a good battery charger and using it in place of a converter -- won't have the 20-30 amp power supply capabilities of the converter for running appliances, but will prolly be more than adequate for most users. The charger will likely be a lot lighter than the converter.

One other function the converter often does is provide a fuse panel for the 12VDC circuits, so if you don't already have a fuse panel, you would need to install one.

On an old 16' Jayco I had, the fuse panel was separate so I just yanked the converter and wired up the charger. On my '91S13, the fuse panel was inside the converter, so I took it out before yanking the converter. My charger is not hard-wired as the battery is right out on the tongue so I just clip the charger on when needed (actually not often as I usually rely on the truck to charge the Scamp battery when driving and I seldom camp with hookups).

The West Marine site has a lot of info on batteries and chargers and a good line of smart tech chargers.

Pete and Rats
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Old 04-23-2003, 07:24 AM   #4
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Chargers, Et Al.

Suz, (incorrectly addressed to T&J at first, edited after reading T&J's response), I pretty much agree with Pete. Although I don't think car alternators make very good recharging devices for depleted deep cycle batteries. Oversimplified, they charge to a voltage level. They don't put back in the amp-hours drained by your lights, water pump, fan, etc. Dedicated chargers, and newer converters are much more efficient at stuffin' those electrons back into the battery. I believe that even a solar panel (50W or 75W) with a charge controller would be more efficient than a car/truck alternator. Alternators are well suited to "starting" type batteries.

In my sail boat, I had to wire in a power resistor (switched) into the circuit to fool the alternator into thinking the batteries were more discharged than they were. That way the alternator puts out a high voltage for a longer time and I finally get some useful charging performance.

While AGM and gel batteries have some attractive points, they seem to always have significantly less amp-hour capacity than the old lead-acid standby. And for the price, I can buy several lead-acid batteries. Different strokes I guess.

The only downside to running off a battery/charger system is that most single battery bank chargers I've run across are about 10amps. That means 10amps into the battery. Leaving the battery could be a couple 18w bulbs (-3.0 amps) and, say, your cabin fan (-2.0 amps for a Fantastic Fan on low). In this example, 5 amps leaving while 10 amps enters. That makes 5 amps for recharging, at least while the DC loads are on. Its just slower, not un-doable.

Hmmm. I just had a thought. According to me, (and what kind of source is that?) alternators suck for recharging deep cycle batteries. Chargers are better. Time out for some math. A 10A, DC charger needs about 150 watts (10A x 14.5V equals about 150 watts) Chargers are only about 90% efficient. 170 watts in to get 150 watts out. While traveling, why not plug the charger into an inverter? Normal inverters are spectacularly inefficient with inductive loads (a charger), so assume 50% efficiency. You'd need about a 350 watt inverter, plugged into the car battery (not the trailer battery) to see killer recharging from your car/truck alternator.

I wonder if this makes any sense. Pete? Morgan? Anyone....? Anyone....? Anyone....? (obscure movie reference)
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Old 04-23-2003, 08:37 AM   #5
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Wait a minute. I (T&J) was(were) just being dictionary here for word clarification. Suz is the one who wanted names and numbers. Course I think that information is here too, but fair is fair. So Tell Suz what to buy for her 16 foot beauty. (I'm going crazy here :crazy-ii)
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Old 04-23-2003, 08:57 AM   #6
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Sorry Jana, I wasn't careful in addressing my note. :red I was extending the discussion along a path that perhaps wasn't originally intended. Suz is/was looking for general information rather than a specific recommendation.
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Old 04-23-2003, 04:12 PM   #7
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Steve, despite the published numbers for fantastical fans on high, medium and low, I suspect they draw the same total power regardless of switch position (the motor may draw less but that's not the total power) because the switch has resistive wires (look down on the fan from above and you will see a screened circular vent for heat dissapation) which I presume drop the voltage to the motor... Bummer!

I once tried powering my charger with my inverter to recharge my dismounted house battery in my front seat and it worked but was cumbersome. Not long after that, my poor old inverter gave up the ghost (the little cooling fan never did work) - Coincidence? I dunno but I prolly won't do it again.

KISS-Keep It Simple Stupid In keeping with KISS, I am reminded of an extremely knowledgeable scientifically-oriented poster to rec.outdoors.rv-travel who normally tweaks stuf to the nth degree. When it comes to batteries, he just buys two WalMart deep-cycles and replaces them every other year rather than trying to nurse them into long life. On the road, I believe he uses the automotive charging system and at home he uses a three-stage charger to maintain them.

I suspect he has the most practical solution for users at our leve. It would be different if we had a bank of four or six 6VDC batteries to replace, like some of the land-barge BulgeMobiles do...

If you already have a converter that isn't smart, the simplest thing to do is not use it for long-term storage (or put a daily timer on it) and plan to replace batteries every few years. Back to the original question, if I didn't have a converter, I'd spend my money on a good charger and use the change to buy the next battery...

Pete and Rats
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Old 04-24-2003, 07:31 AM   #8
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Batteries

Two Batteries: I desperately want a solar panel, but a bit pricey for me at the moment. Too many other toys demanding my financial attention. For my next boonbocking trip I already have the plastic box and a 7 pin socket I plan to install on it. Then, off to WalMart for the battery. This'll do until I can spring for a solar panel.

Fantastic Fan: I know from where you come. Does a light on a dimmer use less current when dimmed? Last fall I installed a Link 10 battery monitor. Pretty cool. It reports 1.9/2.3/3.0 amps on low/med/high. It all seems slightly counter intuitive, but for the moment I'm going to buy off on different current draws.
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Old 04-24-2003, 09:02 AM   #9
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Quote:
Orginally posted by steve L.

Fantastic Fan: *I know from where you come. *Does a light on a dimmer use less current when dimmed? *Last fall I installed a Link 10 battery monitor. *Pretty cool. *It reports 1.9/2.3/3.0 amps on low/med/high. *It all seems slightly counter intuitive, but for the moment I'm going to buy off on different current draws.

Steve: Your previous post is confusing, why not just run a heavy wire to car to charge directly off alternator instead of complication and losses of two conversions? You must have had an reason for avoiding the obvious. Many cars nowadays with all the options and accessories have alternators oversized for their needs.


It need not be counterintuitive, Use Ohm's law, V=IR and you will see dimmers do reduce power useage. True a rheostat (dimmer)or resistor (fan speed switch) does consume some power to lower voltage but its presence in the circuit also reduces total circuit current flow and thus the total power consumed is reduced, sometimes significantly.
I won't bore you with the numbers unless you want me to, but using Ohm's Law and that P=VI, power can also be expressed as P=I^2 R. We can thus see that a small reduction in current reduces power much more "quickly" than a small increase in resistance does to increase it. The real problem is that does a dimmer really produce useful lighting source? As bulb filaments' voltage is lowered from their design voltage, their light output tends to reduce to virtually nil very "quickly".
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Old 04-24-2003, 09:09 AM   #10
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Current situation

I have a regular battery that requires water and exterior ventilation. I have the converter that came on my '89 Casita that also has the fuses on it.

Question: How do I know if I can use a gel type battery with my current converter? Reason I want a different battery is that it location is right under my head where I sleep, it is the acid type (?), plus it is hard to get to for service.

Now: Based on this, what are the recommendations?
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Old 04-24-2003, 09:14 AM   #11
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Alternators as Charging Devices

Joe,

Alternators are poor devices for recharging deep cycle batteries. While they can be heavy duty, that is, put out heavy amperage to offset heavy draws, the automotive controllers don't replace the amp-hours consumed from a deep cycle battery. In marine applications, they sell separate charge controllers. West Marine has articles describing the limitations of automotive regulators.


By the way, I'm a firm believer in Ohm's law. (It's not just a good idea, it's the LAW!:) )
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Old 04-24-2003, 09:22 AM   #12
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Chargers

Suz,

Gel batteries require different voltages for the different charging stages. To optimize battery life, I believe the charger (or converter with built in charger) should have a switch for lead acid vs. gel.

Here's an article that describes the different charging cycles.
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Old 04-24-2003, 09:49 AM   #13
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alternator charging. I just had something changed on the Escape (my tow-er) by the manufacture. the cooling fans drew too much juice for the alternator to keep up and run lights or recharge anything. so to add another battery would have been very bad. now if I got a new alternator then maybe I could now. (I might have got fans though. I can't remember. But as I contemplate, it was the alternator. so I'm good to go. :))
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Old 04-24-2003, 10:15 AM   #14
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[quote]Orginally posted by steve L.

Joe,

Alternators are poor devices for recharging deep cycle batteries. While they can be heavy duty, that is, put out heavy amperage to offset heavy draws, the automotive controllers don't replace the amp-hours consumed from a deep cycle battery. In marine applications, they sell separate charge controllers. West Marine has articles describing the limitations of automotive regulators.

Thanks Steve : I read that link, very interesting! As it states, alternators can indeed put out large amounts of current on demand, and we all know that to recharge a battery we need to replace used amp hours by applying a charge of x amps for y hours. The problem as stated by that link is common to all batteries, not just deep cycle in that as battery gets charged it draws (demands) less current from alternator. So despite the fact an alternator has high current ability it is not being utilized as battery nears full charge because battery voltage approaches alternator output voltage (which is always slighlty higher to induce charging and to overcome battery's internal resistance). This just means an alternator will take time to fully charge a battery but does not necessarily make it a "poor" choice for a charger, time is merely the limiting factor. If travelling. a long drive is often just what the doctor ordered. This regulating action of the alternator can be beneficial as it prevents overcharging and the accompanying boiling off of the electrolyte. And thus an alternator can be left attached/active with little worry. True other controllers can charge more quickly by keeping charge voltage and thus applied current high LONGER as battery voltage recovers. Note: This change in voltage we are talking about often is only a couple of tenths of a volt. A couple of tenths can make all the difference. A float charger might apply 12.8V to a 12.6V cell and thus "maintaining" charge without draining or overcharging, as often 13.0V+ is needed to induce active charging.
Thus i still think that an alternator will do an ok job when compared to the inefficient double conversion from dc to ac back to dc riggamaro.
Thanks, Great posts!
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