Is 35 amps enough capacity for a charge controller? - Page 2 - Fiberglass RV


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Old 04-17-2016, 05:52 PM   #15
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Originally Posted by Jon Vermilye View Post
The problem with a volt meter is the only time it gives you an accurate picture of the state of charge of your battery is when there is no load & no charger (either converter or solar controller) connected. For those with solar panels without a panel disconnect (the usual method of wiring them) you can only check the state of charge with a volt meter after dark.

The advantage of the Bogart (or any other battery monitor) is that they track amp hours, both into & out of the battery. This provides a more accurate measurement of the state of charge whether the sun is shining or not, day or night, with or without the converter charging, etc. It is a bit more involved to set up, but the instructions will get you started, and a phone call to Bogart will provide for any unanswered questions.

A volt meter is fine for those that spend most of their time hooked up or driving every couple of days (to charge the battery from the tow vehicle) but for those that do long time dry camping, particularly for those using a fair amount of amp hours, you will find a battery monitor a useful addition.
I am wondering, Jon, what happens to the monitor readings if the converter charger and the solar charger are connected to to the battery at the same time.

Or, even if not connected simultaneously, how does the monitor handle power input coming from different sources at different times.

I suspect it will give unreliable results and that to avoid this it would be best to, in general, not connect the battery to the converter charger.

Just not sure if the converter charger loses any capability by not being connected to the battery when running on 120 volts.
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Old 04-17-2016, 05:53 PM   #16
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100 amp shunt. It's a resistor. One percent off is 1 amp. Raz
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Old 04-17-2016, 06:00 PM   #17
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100 amp shunt. It's a resistor. One percent off is 1 amp. Raz
Does that mean that as the monitor displays, for example, solar panel charging current, which for example is really 5 amps, the monitor could display anywhere between 4 and 6 amps?

What is the function of the shunt? Is the monitor measuring a voltage differential across the shunt for some reason? Voltage drop somehow indicates current flow? V=IR maybe?
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Old 04-17-2016, 06:11 PM   #18
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The current used battery charging (house battery) is only high when the battery is mostly run down.
Second the wiring in most trailers is sized for 20 amp. Anything above that and you risk fire.
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Old 04-17-2016, 06:16 PM   #19
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Originally Posted by Ransom View Post
Maybe you mean the Parallax 4445/TC? Or is the 7300 maybe an OEM version of the 4445?

The Snoozy standard WFCO float parameters better match the Trojan battery I'll be using (the bulk and absorption charges are the same on the two brands).
Pretty sure at some point Casita used a Parallax 7300 - may be a newer/different model number now. I was pretty sure on it as I helped a friend with deciding on a replacement when their original one failed so I had a note on my phone re its details.
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Old 04-17-2016, 06:26 PM   #20
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The current used battery charging (house battery) is only high when the battery is mostly run down.
Second the wiring in most trailers is sized for 20 amp. Anything above that and you risk fire.
OK Byron, then to add perspective I need to find out what the rating is of the 12 volt circuit breaker on the Snoozy (and the breaker for the 120 volt side).

Good point.

I am surprised that there is so much to know to fully understand these systems.

I think the biggest frustration is that the manufacturers of the trailers dont publish these details, and, clearly, the manufacturers of the charge converters and other devices either don't provide the specs on their websites, or they make it difficult to find.

It is no wonder many people have problems later or swap out equipment for alternatives.
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Old 04-17-2016, 07:48 PM   #21
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Ransom,
35 amps will be plenty. Your water pump might be 7.+ amps per HOUR but you'll run out of water after a few minutes anyway (3.5 GPM divided by your gallons of fresh water). An amp will probably drain your fresh water tank. There are a lot of good reasons to upgrade a converter IF you need to and that depends on how you're going to be using the rig. Don't worry about figuring it all out, if you RV long enough you'll learn what you need to know.

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Old 04-17-2016, 07:54 PM   #22
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Originally Posted by Ransom View Post
Does that mean that as the monitor displays, for example, solar panel charging current, which for example is really 5 amps, the monitor could display anywhere between 4 and 6 amps?
Correct. An experiment. Set your voltmeter on the 20 v scale and measure your 12 v battery. Now set it on the 200v scale and do the same measurement. Notice you just lost the least significant digit. Higher scale less accuracy. Now try it with a D cell.

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What is the function of the shunt? Is the monitor measuring a voltage differential across the shunt for some reason? Voltage drop somehow indicates current flow? V=IR maybe?
Current flows through a wire. To measure it, a small resistor is placed in the circuit and the voltage across that resistor is directly proportional to the current. yes, ohms law. The catch is that the resistance needs to be small enough not to become part of the circuit and effect the current you are trying to measure but large enough to give you a readable voltage. With a 100 amp shunt you get a very, very small voltage with the low currents seen with a single battery. . Too small in my opinion.
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Old 04-17-2016, 08:07 PM   #23
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Carol, yes, ours is a 7345; 7300 series, 45 amps. Casita is apparently now providing a 7155; 30 Amp AC and 55 Amp DC.

Ransom,

Our water pump, a Flojet, apparently draws 5.2 amps. The water pumps in small RV's are generally fixed-speed and run pretty much when the water is flowing. Then they shut off.

Regarding the 45 amp rating, I guess one man's overkill might be another man's security. I am not clear what the peak charging load is with this set-up and can't speak to Casita's reasoning in supplying the 45 amp units, and now apparently 55 amps capacity since 2015.

There are apparently quite a few people that add a more sophisticated battery charger to use with the Parallax in the Casitas. I have also noted that a good number of folks swap out the Parallax for a Progressive Dynamics. The swaps are generally when the originals fail as the PDs cost a bit.

Regarding the availability of information concerning RVs and their equipment, that is why the common wisdom is to buy your third RV first. Starting with molded fiberglass is generally a good choice, but even that doesn't work for everybody. It's all very personal.

By the way, if North Carolina were more conveniently located on the left coast, nearer to where I am, I might own one as the Mrs. and I like their layout. I sure hope it turns out to be the right one for you.
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Old 04-17-2016, 08:12 PM   #24
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Carol, yes, ours is a 7345; 7300 series, 45 amps. Casita is apparently now providing a 7155; 30 Amp AC and 55 Amp DC.

Ra.
Thanks for the conformation - I wasn't sure why I would have that model noted in my phone if it had not been correct.
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Old 04-17-2016, 09:02 PM   #25
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Correct. An experiment. Set your voltmeter on the 20 v scale and measure your 12 v battery. Now set it on the 200v scale and do the same measurement. Notice you just lost the least significant digit. Higher scale less accuracy. Now try it with a D cell.


Current flows through a wire. To measure it, a small resistor is placed in the circuit and the voltage across that resistor is directly proportional to the current. yes, ohms law. The catch is that the resistance needs to be small enough not to become part of the circuit and effect the current you are trying to measure but large enough to give you a readable voltage. With a 100 amp shunt you get a very, very small voltage with the low currents seen with a single battery. . Too small in my opinion.
How does that work, Raz...?

If the voltage from the charge controller is, say 14.4 volts (bulk charge level), current flows through the shunt (resistance) and into (through?) the battery.

Trying ohms law, using 99 ohms for the shunt, you get i = .145 amps, and for shunt of 101 ohms you have .143 amps. But actual current at 100 ohms shunt is .144 so accuracy is .001 volt, or 0.69% accuracy, very accurate.

This math can't be right because the battery, at bulk charge, would draw many amps, and, you advise the current reading accuracy is much worse.

Can you explain?
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Old 04-17-2016, 09:15 PM   #26
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Carol, yes, ours is a 7345; 7300 series, 45 amps. Casita is apparently now providing a 7155; 30 Amp AC and 55 Amp DC.

Ransom,

Our water pump, a Flojet, apparently draws 5.2 amps. The water pumps in small RV's are generally fixed-speed and run pretty much when the water is flowing. Then they shut off.

Regarding the 45 amp rating, I guess one man's overkill might be another man's security. I am not clear what the peak charging load is with this set-up and can't speak to Casita's reasoning in supplying the 45 amp units, and now apparently 55 amps capacity since 2015.

There are apparently quite a few people that add a more sophisticated battery charger to use with the Parallax in the Casitas. I have also noted that a good number of folks swap out the Parallax for a Progressive Dynamics. The swaps are generally when the originals fail as the PDs cost a bit.

Regarding the availability of information concerning RVs and their equipment, that is why the common wisdom is to buy your third RV first. Starting with molded fiberglass is generally a good choice, but even that doesn't work for everybody. It's all very personal.

By the way, if North Carolina were more conveniently located on the left coast, nearer to where I am, I might own one as the Mrs. and I like their layout. I sure hope it turns out to be the right one for you.
I agree with you Civilguy, it doesn't make sense to upgrade the power capacity of the converter/charger for these fiberglass trailers, unless people are usung some other high current appliances...what could that be, are we missing something?

Or maybe it is because these units put out only a handful of amps for bulk charging, and batteries can safely accept higher current, and the higher rated converters probably allocate more current to charging?

It is curious.

What does it mean "buy your third rv first"....does it mean we tend to not really understand the details of our first purchases (nor of our ultimate needs)? If that"s it, you are so right.

But it is clear why that is the case....the vendors don't explain or document (and often don't know themselves), good knowledge-based recommendations are not given, and customers don't even know what questions to ask.

I think if the trailer manufacturers were to do an excellent design, with cost-effective, truly useful features, most customers would not understand and choose lower cost products from competitors.
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Old 04-17-2016, 10:08 PM   #27
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Ransom,
One of the reasons why someone might upgrade their converter/charger is to pump more amps into their batteries like you stated, most of the old converters are only providing 6-8 amps on a old fashion taper charge (hummmm). Newer chargers offer much higher amperage with multi-stage charging that monitor the batteries much closer. They have much cleaner electric, no hum, less RFI and have provisions for AGM and Gel Cell batteries which charge much faster than lead acid batteries.

If you're boondocking a lot for extended periods and running a generator to charge the batteries, upgrading the charger and batteries will probably make sense. If you're weekending and vacationing in RV parks with electric why bother unless there is a problem.

I have no earthly idea why a Casita would need 55 amps? I guess it isn't hurting anything.

Bill

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Old 04-17-2016, 10:31 PM   #28
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I agree with you Civilguy, it doesn't make sense to upgrade the power capacity of the converter/charger for these fiberglass trailers
I only said I can't speak to why Casita is supplying these units, not that it doesn't make sense. For different situations it could be a matter of utilized capacity, reserve capacity, better power quality, improved vitality and hair growth...

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What does it mean "buy your third rv first"
I think that old expression acknowledges that it takes time to figure out what you really want and even then it often changes over time. At an extreme, there was a listing for an essentially new molded trailer last year. As I recall, it was stated in the ad to have been used only one night since delivery; the owners decided they would enjoy themselves more in their back yard and listed it for immediate sale.
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