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


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Old 04-17-2016, 01:16 PM   #1
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Is 35 amps enough capacity for a charge controller?

I am hoping to purchase a Lil Snoozy, and am unsure if I the standard Arterra WF9835 35 amp unit is adequate.

Amperage demand includes:

0.0 amps water heater (runs on 120 vac only so not usable wth 12 volts)
7.5 amps water pump
2.2 amps refigerator (Nova Kool R3800) duty cycle is approx 50%, but when running draws 2.2 amps
1.3 amps LED light fixtures (5 x 0.25 amp)
3.0 amps Fantastic Fan - high speed
2.1 amps USB charger
3.6 amps estimated for battery charging
_________
20.0 amps total

If other devices are added the load increases. Of course it would be a rare instance when all loads are in use simultaneously.

I am guessing running the converter at close to max capacity creates a lot of fan noise, shortens usable life, and could trip the circuit breaker when surge currents happen such as when the refregerator motor turns on.

Is this really all the 12 volt demand would be in a typical fiberglass rv trailer? If so, a 35 amp system would probably run cool, quietly, and well under capacity... no advantage to upgrade to a heavier, larger 45 amp unit except for the fact that a larger unit is probably going to allocate more of the available current to the battery charger, giving a faster chsrge.


Is my logic correct or are their other considerations?

NOTE THE ABOVE DETAIL WAS JUST REVISED BASED ON RAZ'S INPUT.
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Old 04-17-2016, 02:11 PM   #2
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Originally Posted by Ransom View Post
I am hoping to purchase a Lil Snoozy, and am unsure if I the standard Arterra WF9835 35 amp unit is adequate.

amperage demand includes:

12.5 amps water heater
7.5 amps water pump
2.2 amps refigerator (Nova Kool R3800)
5.0 amps LED lights (5 x 1 amp)
3.0 amps Fantastic Fan - high speed
2.1 amps USB charger
3.7 amps estimated for battery charging
_________
36.0 amps total

I doubt the water heater is run on 12 volts so no converter there. The water pump sounds high. Mine uses 2-3 amps. And if the LEDs are using an amp each they're junk. More like 0.2 amps each, or one amp for the lot. Charger and fan agree with what I would expect to see. The fridge seems low. I suspect you'll be fine. How long do you have to wait to get your trailer? Happy shopping, Raz
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Old 04-17-2016, 03:01 PM   #3
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My Casita has a 45 amp power supply. I bought the trailer used, but I think this is "standard" for this trailer.

In broad terms, running electrical equipment at lower loads will reduce operating temperatures and wear.

If your trailer is all electric, (i.e. no LP gas), then you may find some benefit now or in the future.

If the additional cost seems reasonable to you, that might be your decision maker.
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Old 04-17-2016, 03:10 PM   #4
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Originally Posted by Raz View Post
I doubt the water heater is run on 12 volts so no converter there. The water pump sounds high. Mine uses 2-3 amps. And if the LEDs are using an amp each they're junk. More like 0.2 amps each, or one amp for the lot. Charger and fan agree with what I would expect to see. The fridge seems low. I suspect you'll be fine. How long do you have to wait to get your trailer? Happy shopping, Raz
Good points Raz! I have updated the matrix. The fridge does indeed draw 2.2 amps. The water pump is , I think, a Shur Flo 4008, drawing 7.5 amps (thats probably the surge current rating).
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Old 04-17-2016, 03:12 PM   #5
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The charger/converter converts the 110AC to 12 VDC to charge the maintain the battery. Your 12 volt components are supplied directly by the battery so the amp rating of the converter is not that critical. My LilSnoozy has the 35 amp unit and does just fine.

Don
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Old 04-17-2016, 03:18 PM   #6
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Originally Posted by Civilguy View Post
My Casita has a 45 amp power supply. I bought the trailer used, but I think this is "standard" for this trailer.

In broad terms, running electrical equipment at lower loads will reduce operating temperatures and wear.

If your trailer is all electric, (i.e. no LP gas), then you may find some benefit now or in the future.

If the additional cost seems reasonable to you, that might be your decision maker.
After this analysis, using Raz's corrections, I am surprised that you have 45 amps in the Casita. The Snoozy is no gas, all electric. It seems that more than even 20 amps would rarely be needed and the typical demand would be cosiderably lower.

Are there other 12 volt devices that are commonly used? If not, maybe the only reason to go with a 45 amp system is for allocating more current to charge the battery in cases where it has been substantially depleted for boondocking.

Seems that 45 amps is overkill.
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Old 04-17-2016, 04:26 PM   #7
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Originally Posted by Don W3NDT View Post
The charger/converter converts the 110AC to 12 VDC to charge the maintain the battery. Your 12 volt components are supplied directly by the battery so the amp rating of the converter is not that critical. My LilSnoozy has the 35 amp unit and does just fine.

Don
That is a very good point! With the battery connected you have a huge source of backup power, so peak demand is much less of an issue.

I believe the converter charger output, the battery, and the 12 volt loads (from the electrical panel) are normally all connected together.

When there is no load, the voltage level on all (set by the converter/charger) is 13.2 volts (float voltage).

This rises to 3.6 volts when any load is present.

When the battery needs charging it receives 14.4 volts from the converter/charger for bulk charge, 13.6 volts for absorption level, and 13.2 for float, but the converer goes back to absorption (13.6) when any load is present (for example fridge kicks in).

So, the loads see these varying voltage levels, depending on the needs of the battery.

These converters are very basic chargers.

I am going to install a 100 watt solar panel with the Bogart TM2030RV monitor and SC2030RV smart solar charger and program the charge parameters to match the Trojan battery I will buy.

These stock converter chargers do not allow matching to the batteries so battery life is shortened and many times full charge will not be achieved, sacrificing amp hours available when boon docking.

For these reasons I am thinking to always use the rooftop solar panel for battery charging (and equalization, another thing the converter charger wont do).

I will normally never connect the battery to the converter charger, whether on campground ac or not. In addition, in ths way, when on ac, the 12 volt loads will always see a consistent13.6 volts.
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Old 04-17-2016, 04:57 PM   #8
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For what it's worth, buy a voltmeter, skip the monitor. People buy them not realizing that the smallest shunt is 100 amp. With a single battery your typical current will be less than 10 amps; many times less than 1 amp. Even if the accuracy were 1% you're still +/- 1 amp. Because it has a digital read out, folks assume accuracy. Raz
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Old 04-17-2016, 05:18 PM   #9
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For what it's worth, buy a voltmeter, skip the monitor. People buy them not realizing that the smallest shunt is 100 amp. With a single battery your typical current will be less than 10 amps; many times less than 1 amp. Even if the accuracy were 1% you're still +/- 1 amp. Because it has a digital read out, folks assume accuracy. Raz
I disagree, not with your figures but about the monitor. The Trimetric works with the Bogart controller to enhance the controller's efficiency. In addition the Trimetric has other attributes that can be informative.
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Old 04-17-2016, 05:23 PM   #10
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For what it's worth, buy a voltmeter, skip the monitor. People buy them not realizing that the smallest shunt is 100 amp. With a single battery your typical current will be less than 10 amps; many times less than 1 amp. Even if the accuracy were 1% you're still +/- 1 amp. Because it has a digital read out, folks assume accuracy. Raz
I think you mean at 10 amps 1% accuracy is 0.1 amp, plenty of accuracy. I guess you are right, with a voltmeter and ammeter you can monitor most of what is useful.

I have two volt/amp meters and a wattsup meter, but I've never had an rv before so don't really know what's most important.

Before buying the Snoozy I want to know all its details and plan the configuration well. Fewer surprises and changes later.

I think Raz, the advantage of the monitor is that voltage and amps can be measured without changing the way the meter is connected, and there are many other interesting and useful features (battery % full, low battery alarm, days since equalized..) that are especially helpful when boondocking and efficent charging and power use is key.
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Old 04-17-2016, 05:31 PM   #11
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I disagree, not with your figures but about the monitor. The Trimetric works with the Bogart controller to enhance the controller's efficiency. In addition the Trimetric has other attributes that can be informative.
I didn't realize that, Timer Wolf, that the monitor improves the efficiency of charging (I assume you mean automatically)... and that is a compelling reason to use the monitor...especially in my case, with the match of a group 24 battery and a 100 watt solar panel, the solar panel output/efficiency is more critical than the battery capacity.

The issue is that with the limited non-curving real estate on the Snnozy roof, and variable panel angle mounting considerations, the practical installable solar capacity falls short of ideal.
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Old 04-17-2016, 05:31 PM   #12
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I am surprised that you have 45 amps in the Casita. The Snoozy is no gas, all electric. .
Casta used the Parallax 7300 power converters which are 45 amps.
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Old 04-17-2016, 05:35 PM   #13
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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.
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Old 04-17-2016, 05:43 PM   #14
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Casta used the Parallax 7300 power converters which are 45 amps.
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).
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