2 Quick questions RE: charger/monitor operation - Fiberglass RV


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Old 07-28-2017, 03:36 PM   #1
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2 Quick questions RE: charger/monitor operation

I'm buying a 12v Group 24 75ah deep cycle battery for my Scamp 13' trailer. I'm also considering buying a CTEK 4.3 8-step automatic charger/monitor.

Question:

When I'm plugged in to 120v and camping - running the fridge off 120v, the tiny lights, etc. ~ can I recharge using this charger (while there's also a drain on the battery)? Or should I just check on the battery every day and charge it while not using anything that drains the battery?

For example, if I plug in upon arrival at camp and leave it overnight until I leave the next day ~ will it have recharged the battery during those 24 or so hours? If so, will lots of small recharges damage any battery I might purchase?

Thanks!
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Old 07-28-2017, 05:12 PM   #2
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Quote:
Originally Posted by JC_In_Austin View Post
I'm buying a 12v Group 24 75ah deep cycle battery for my Scamp 13' trailer. I'm also considering buying a CTEK 4.3 8-step automatic charger/monitor.

Question:

When I'm plugged in to 120v and camping - running the fridge off 120v, the tiny lights, etc. ~ can I recharge using this charger (while there's also a drain on the battery)? Or should I just check on the battery every day and charge it while not using anything that drains the battery?

For example, if I plug in upon arrival at camp and leave it overnight until I leave the next day ~ will it have recharged the battery during those 24 or so hours? If so, will lots of small recharges damage any battery I might purchase?

Thanks!
You can charge your battery while it is under a load.
If the charger puts back more than you use, it should be recharged overnight.
You might consider Charging from your TV while underway as well.

As CTEK says..."Connect and forget"
As for Swedish quality....who knows?

Here is more...

https://shop.advanceautoparts.com/p/...&gclsrc=aw.ds#
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Old 07-28-2017, 07:51 PM   #3
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Think about the answer to your question by relating it to something you do fairly often. .... You are driving at night down the highway with your lights on and the radio playing and at the same time the alternator in your car is recharging your battery.

That makes the answer pretty obvious
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Old 07-28-2017, 11:09 PM   #4
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Originally Posted by k corbin View Post
Think about the answer to your question by relating it to something you do fairly often. .... You are driving at night down the highway with your lights on and the radio playing and at the same time the alternator in your car is recharging your battery.

That makes the answer pretty obvious
Really? It's quite obvious with a car battery charged via an alternator. However, I've never had a trailer before; I bought it two weeks ago yesterday and only discovered the damaged battery a couple of days ago. I know it will charge some while I'm using it, but I specifically asked:

(1) will it [the low voltage charger] have recharged the battery during those 24 or so hours? and
(2) If so, will lots of small recharges damage any battery I might purchase?
------------------------
The charger is 4.3 amps, so I don't know whether it will charge the battery adequately in a short time while it's also being drained and, if so, whether that hurts the battery.

I'll try not to be so slow-witted if I ever ask another question here.
Thanks.
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Old 07-28-2017, 11:17 PM   #5
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Quote:
Originally Posted by floyd View Post
You can charge your battery while it is under a load.
If the charger puts back more than you use, it should be recharged overnight.
You might consider Charging from your TV while underway as well.

As CTEK says..."Connect and forget"
As for Swedish quality....who knows?

Here is more...

https://shop.advanceautoparts.com/p/...&gclsrc=aw.ds#
Thank you, Floyd; I appreciate the help! / JC
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Old 07-29-2017, 01:58 AM   #6
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As long as your battery charger puts out more than the average load you have on the battery, it will charge up completely. Can't say how long that might take (overnight?), but it will. It's a good idea to get a charger that has more output than you think you might need, and one that is a smart charger with a multi-stage charging program. There are three stages to battery charging: Bulk, absorption and float. Some will equalize too. This feature runs the voltage up to about 16 volts occasionally to prevent sulfation. I don't know about the "8 step" charger you referenced.

A deep cycle battery is designed to be discharged and re-charged many times as long as it isn't run down more than about 50% each time. It will not hurt the battery to discharge it to 50% and charge it back up, over and over.

It's also a good idea to charge it from the tow vehicle while driving. That brings it up to about 14.1 volts and holds it there while the engine is running. While plugged in, and fully charged, the battery charger will hold the voltage at about 13.2 volts (float voltage). This is how you maintain a healthy, flooded cell, battery.

BTW, if you can fit it in your battery area, get a Group 27 instead of a Group 24, for the extra capacity.
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Old 07-29-2017, 04:03 AM   #7
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Hi Judy, just a couple things for you from my 30+ years RVing and I'm not knocking any others suggestions/comments here. I quit using any deep cycle batteries maybe 25 years ago and started using a standard car type battery, 24 or 27 because the charge time was so much less than a deep/marine cycle battery. These were all in class Cs or A motorhomes with no LED lights or TVs ect. On trips of 2 weeks boondocking I would run the engine for about 15 minutes every 3rd day to charge it up and never had a problem with power. But back to your TT. Charging your TT battery while on the road is going to be determined by the tugs alternators output and the gauge of the wire going back to the TT with a 7 pin plug. If I remember correctly, you're new to RVs, toss a battery in it, go out and go camp. I can guarantee there's not one person here that didn't do a lot of learning a long the way .
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Old 07-29-2017, 07:45 AM   #8
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Quote:
Originally Posted by JC_In_Austin View Post
I'm buying a 12v Group 24 75ah deep cycle battery for my Scamp 13' trailer. I'm also considering buying a CTEK 4.3 8-step automatic charger/monitor.



Question:



When I'm plugged in to 120v and camping - running the fridge off 120v, the tiny lights, etc. ~ can I recharge using this charger (while there's also a drain on the battery)? Or should I just check on the battery every day and charge it while not using anything that drains the battery?



For example, if I plug in upon arrival at camp and leave it overnight until I leave the next day ~ will it have recharged the battery during those 24 or so hours? If so, will lots of small recharges damage any battery I might purchase?



Thanks!


I recently changed my Group 24 battery to two 6 volt golf cart batteries which gives us 220 amp hrs. I changed my charger to a C Tec 25 amp. It does a great job. Just hook it up and forget it. I recommend a battery monitor. The charger has one on it but mine is not where I can see it at a glance so I use one of the cheap ones that plug into a 12v outlet.
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Old 07-29-2017, 07:55 AM   #9
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Quote:
Originally Posted by JC_In_Austin View Post
I'm buying a 12v Group 24 75ah deep cycle battery for my Scamp 13' trailer. I'm also considering buying a CTEK 4.3 8-step automatic charger/monitor.

Question:

When I'm plugged in to 120v and camping - running the fridge off 120v, the tiny lights, etc. ~ can I recharge using this charger (while there's also a drain on the battery)? Or should I just check on the battery every day and charge it while not using anything that drains the battery?
Yes, leave the charger on when shore power is available. It is OK to use loads and the charger at the same time. Some chargers might be “confused” when the voltage changes as loads come online or go offline, but the manual for this charger does mention using it (on a vehicle) when there are loads present.

Quote:
Originally Posted by JC_In_Austin View Post
If so, will lots of small recharges damage any battery I might purchase? ...
Shallow discharges are better for the battery than deep discharges, even if they are more frequent.

Quote:
Originally Posted by JC_In_Austin View Post
For example, if I plug in upon arrival at camp and leave it overnight until I leave the next day ~ will it have recharged the battery during those 24 or so hours? ..
First, understand amps vs. amp-hours (Amp-hour). Amp(s) is the measure of the current flow at a particular point in time. Amp-hour is a unit of electric charge, calculated as current multiplied by time. One Amp-hour is equal to the charge transferred by a steady current of one amp flowing for one hour. Think of amps like the amount of water going through a pipe at a moment in time, and Amp-hours as the total amount of water in the tank (or total power).

If, in your camper, you use a steady 4.3 amps for one hour, you have consumed 4.3 amp-hours total. It would be the same is you used a steady 2.15 amps for two hours. The charger you are considering can deliver 4.3 amps*. If you stopped using the battery as just mentioned and then connect the charger for one hour, you have returned the 4.3 amp-hours to the battery. If the charger is connected while you are using 4.3 amps in one hour then it’s a wash and your battery is still full.

So to know if the 4.3 amp charger is sufficient for your needs you need to know what your power usage is. That is how many amps are you using, and for how long are you using them. This page gives some averages for common appliances. Once you know that, its simple math. (A recording amp monitor with shunt can monitor your power use automatically).

Let’s take a look at a simple example. My roof fan uses about 2.5 amps on high setting. An incandescent light might use one amp.** If, over an eight hour period, I run my fan and also three one-amp lights for the entire eight hours, I have used 44 amp-hours*** (2.5 amps x 8 hours) + (1 amp x 3 lights x 8 hours). 44 divided by 4.3 is 10.2 so expect the 4.3 amp charger to take over ten hours to recharge the battery.

If the charger was also running the entire time, then subtract the amount of recharge from the amount of discharge. In eight hours the charger can deliver about 34 Amp-hours. Since you used 44 Amp-hours, your battery is still discharged a net of ten Amp-hours (44-34). Now you do the math… how long must the charger be on to return that last ten Amp-hours (assuming no loads).

Where it gets tricky is in how long the loads are on. Things like water pumps draw more current, but they also run for very short periods of time, so the amp-hour use is not so much.

I don’t know anything about your system or your pattern of power use. A 4.3 amp charger with a 75 Ah battery might be OK, but for most people I would suggest something more, maybe a 10 amp charger. But you might also then benefit from a larger battery, something closer to 100 Ahs.

Recommended reading:
The 12volt Side of Life (Part 1)
The 12volt Side of Life Part 2

* Actually recharge will be less due to battery chemistry, system power loss, etc. Expect approximately a 10% reduction, or put another way, add around 10% to recharge time. This applies to all the math examples in this post.

** Of course LED lights use much less power than incandescent and are recommended.

*** While these numbers are just given for easy math, note that the most you should use from the 75Ah battery that you mentioned is about 37 Ah.
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Old 07-29-2017, 09:27 AM   #10
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Raspy / Borrego Dave / Charlsara / Gordon 2

This is exactly the information I needed! It all makes sense now! If one doesn't know ANYthing about batteries (that would be me), all the technical information on the 'net can be very confusing. Hearing from veterans like y'all, willing to share the information is so valuable!

I really, really appreciate all this. Happy trails to all of you!
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Old 07-29-2017, 11:20 AM   #11
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I consider a 4.3 amp charger a maintenance charger to be used when the trailer is stored to keep the battery healthy. Not intended for use when the battery is being used. This charger will not harm your battery when battery is in use but is inadequate for keeping a battery up while in use. A battery can safely accept current at 25% of it's a ampehour rating. Therefore a 75AH battery when discharged to the max it can accept 17 amps. I would lean to a 20A smart charger or converter.
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Old 07-29-2017, 11:23 AM   #12
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PS. Background, we lived on a boat for 9 yrs, batteries were very important. We had to learn battery info fast.
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Old 07-29-2017, 11:58 AM   #13
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Originally Posted by J Ron View Post
I consider a 4.3 amp charger a maintenance charger to be used when the trailer is stored to keep the battery healthy. Not intended for use when the battery is being used. This charger will not harm your battery when battery is in use but is inadequate for keeping a battery up while in use. A battery can safely accept current at 25% of it's a amp/hour rating. Therefore a 75AH battery when discharged to the max it can accept 17 amps. I would lean to a 20A smart charger or converter.
Oh...wow. See, I hadn't thought about that. After I know about what my usage is (won't be boondocking very much, since I generally travel alone), I'll consider getting a hotter charger. Might even send this one back and get a bigger one now.

Thank you very much for putting this out there.

Happy trails! / JC
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Old 07-29-2017, 12:37 PM   #14
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Originally Posted by JC_In_Austin View Post
Really? It's quite obvious with a car battery charged via an alternator. However, I've never had a trailer before; I bought it two weeks ago yesterday and only discovered the damaged battery a couple of days ago. I know it will charge some while I'm using it, but I specifically asked:

(1) will it [the low voltage charger] have recharged the battery during those 24 or so hours? and
(2) If so, will lots of small recharges damage any battery I might purchase?
------------------------
The charger is 4.3 amps, so I don't know whether it will charge the battery adequately in a short time while it's also being drained and, if so, whether that hurts the battery.

I'll try not to be so slow-witted if I ever ask another question here.
Thanks.
The rate of discharge depends on the power drain. Since you might be using different electrical items for different lengths of time you will need to do some math. Unfortunately the only person who can answer that is yourself as you are the person who has those electrical devices in your hands and can read the information posted on their labels that states how much power they draw.
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