Camplite Battery Charging

[charliem]

[font size="3"]As an experiment I compared different methods of battery charging on my 21RBS. The batteries were two 6V golfers in series. I started with the batteries at 11.85V open circuit at 68F after resting *, or about 35% SOC. Using the onboard converter plugged in to shore power the initial current measured 38+ Amps and quickly dropped off. Using 20 ft. #4AWG copper jumper cables from my Tacoma the current initially measured 69A and quickly dropped to 50+ Amps. At 35 minutes it had dropped to 28A at 13.03V. After 1 hour I measured 23A at 13.03V.  Even at 23A I measured 0.3V drop in the 20 ft. #4 copper jumper cables. Charging current is very sensitive to voltage so every 0.1 volt contributes to reduced charging current. Cheap jumper cables won't cut it. After a 30 minute resting period I measured 12.35V, indicating 70% SOC.

Reconnecting the truck for an additional 30 minutes got it to 12.46V resting or 80% SOC. A previous test indicated I used about 30 AH/day with moderate furnace use, lights,  and heavy use of a watt sucking laptop. Thus a 1 hour recharge period every other day would go a long way to extending my dry camping time. The only unanswered question is the time required to recharge to 80%. The jumper cables supplied a higher current, but the onboard converter eventually charges at a higher voltage, 14.4 vs 13.3 for the truck.

Certainly the onboard converter is best where shore power is available, but the jumper cable method provides a viable recharge if shore power or generator are not available. The truck is a whole lot quieter and more convenient than a generator. No gas cans or heavy generators to haul. The truck only burns ½ GPH at idle so just make sure you have a full tank when setting up.

* Resting overnight with only the 170 mA residual load on the battery.

As an aside I tried plugging the Camplite power cord into the 400W inverter built into the Tacoma. The current measured only 3.6A and the microwave display didn't light at all. This is consistent with previous attempts at using the truck inverter to run the CL. Apparently the CL doesn't like the waveform of truck inverter (probably MSW) or the load (38A x 12V) crowbars the inverter. Further investigation is required. If it's because the load is exceeding the 400W rating it's not really useful. EDIT: Turns out I'd left the electric side of the water heater on. That will kill a 400W inverter every time    
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[joanne]

This is the first time I've seen real numbers on using jumper cables from a running vehicle. I've done that in a pinch, but had no idea that it was reasonably effective.

Good info. Thanks.

[leslie]

Maybe I have missed something. I thought using the 7-pin connector and running the engine of the tow vehicle, whether running down the road or just idling, was a quicker way to charge AGM batteries than using jumper cables.

We have been able to bring our batteries back up with about 4 -5 hours driving. We had everything turned off in the trailer except for the refrigerator running on propane, and, of course, the blue light on the radio was on.

[charliem]

[font size="3"]Charging from the 7 pin TV connector is extremely ineffective. This is due to the small wire used between the TV battery and the 7 pin connector and the small wire from the 7 pin to the TT battery. At best it is only able to maintain a charge; maybe recharge slightly. However, given enough time (4-5 hrs) it may restore some charge. If nothing else is running you may get 10 Amps to the TT battery. Notice the 0.3V drop I measured with #4AWG wire. The TV and TT are wired with #10AWG at best; sometimes even smaller. The jumper cable, although a bit inconvenient, is the most effective short of a high powered plug in battery charger. My intent was to deal with the times when I was camped for several days without any shore power hook up. I don't like noisy messy generators and the TV with its engine, muffler, and gas tank is coming along anyway      .

BTW that blue light can be turned off from the menu.
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[pinstriper]

Or, remove the faceplate and put it in the cabinet. Presto ! No more blue light.

[leslie]

I asked my husband to remove that faceplate, because I hate that bright blue light, but he didn't want to touch it. I didn't know I could turn it off from the menu. I will have to give that another look.

My youngest son is a computer and electronic geek. If all else fails, when we visit him in Florida, I will ask him to help me out.

About recharging the batteries using the 7-pin connector - I really don't know how low the batteries got. My husband checked them, said they were low. We drove for 5 hours. He checked again - said they were fine. Now I am wondering just how much confidence I should have in that connector.

[charliem]

[font size="3"]First the blue light. The light will be on while you're using either the radio or the external input. If the radio is on the blue light will be on. When you turn the radio off by holding the mute button down the clock will remain in blue. This can be inhibited from the menu, but it's a bit elusive. Isn't it always? If I'm plugged in I turn off the microwave at the circuit breaker at night. I don't like green lights either.

Now the battery charging. Others have noted the 10 Amp number, but I have not measured it. It's highly dependent on the TV. But let's assume the 10 Amp number is good. As I stated my daily use was about 30 Amp-Hours per day so it would take three hours of driving to recover. If you've been running on battery for three days as I did last week it would take 9 hours of driving. That's a long day for us old folks. Four days on battery and you're in trouble.
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[leslie]

That microwave light annoys me too. I like darkness at night which is just one of the reasons why I want to go boondocking.

After having a house way out in the country for 34 years, with the only night light coming from the moon, I really miss not seeing stars when I walk the dogs at night, not to mention not having a dark bedroom at night. Now, enough light filters in through the curtains that no night light is necessary. This is in our apartment. Some campgrounds let in a lot of light through the window in the door. I am seriously thinking about a window cover for the entry door.

[pinstriper]

[quote source="/post/17199/thread" author="@leslie" timestamp="1450322822"]I asked my husband to remove that faceplate, because I hate that bright blue light, but he didn't want to touch it. I didn't know I could turn it off from the menu. I will have to give that another look.

[/quote]It's easy. All you need is a #5 torx driver and  a slotted screwdriver (that's a "regular" as opposed to "phillips"). 7 small bolts and a little prying with the flat of the screwdriver. 15 minutes tops, and no more blue light.

[leslie]

Back to the thread - Louisville RV does some work for me - filling propane, repacking the bearings, etc. They tell me I can completely discharge my AGM batteries and they will come back just fine if I tow the trailer for a trip or plug in when I get to a campground. They say that is what the AGM batteries are made for.

So far, we have only gone one day at a time on battery power. We plan to work ourselves up to 3 or 4 days on battery power. So long as we are careful, I thought it would be possible to go 5 or 6 days on battery before we have to drive off and recharge.

We are looking - OK, I am pushing - for 5 days on battery power in Quartzsite AZ for January 2017. No generator.

[pinstriper]

Back to the thread - Louisville RV does some work for me - filling propane, repacking the bearings, etc. They tell me I can completely discharge my AGM batteries and they will come back just fine if I tow the trailer for a trip or plug in when I get to a campground. They say that is what the AGM batteries are made for.

So far, we have only gone one day at a time on battery power. We plan to work ourselves up to 3 or 4 days on battery power. So long as we are careful, I thought it would be possible to go 5 or 6 days on battery before we have to drive off and recharge.

We are looking - OK, I am pushing - for 5 days on battery power in Quartzsite AZ for January 2017. No generator.

We got a 75w portable solar panel "free" when we bought our trailer. Looks like a large briefcase and folds out, aligator clips to + and -. Pretty simple, and I used it to top off the battery once when the barn had a circuit issue.

I have no idea how fast it puts how much back on the battery, but I would think such a thing would be a good addition if boondocking in a sunny place like AZ. Way better than nothing at all, anyway. Very compact and easy to bring along.

[mitch]

Leslie, what's your battery setup (how many Amp Hours)?  Five days is a pretty long time.

[whoofit]

They tell me I can completely discharge my AGM batteries and they will come back just fine if I tow the trailer for a trip or plug in when I get to a campground. They say that is what the AGM batteries are made for.

AGM batteries can take a beating but suggesting they can be brought down dead as a door knob and "will come back just fine" is a risky statement. One of the several benefits of AGMs is their deeper Depth Of Discharge. Better than conventional wet lead acid but still can be damaged real good going full dead.

Leslie, I suggest you have them install a battery monitor. One that will tell you what your SOC (state of charge) is. Those will measure the CE (consumed energy) at any given moment. It will tell you how many amps you are drawing at the moment. Some will calculate TTG (time to go) at your current level of discharge (though this is not a very accurate calculation just a reference).

On the flip side, they can measure the amount of energy you have put back into the battery during or after charging and not be tricked by the "skin effect" that plagues most folks when using a simple voltmeter. Most folks say "look, it's full" long before it really is. In the inverse most folks think their battery is discharged when it isn't because of loads present on the battery. A good battery monitor like a Victron will sort through all the BS.

But a word of caution, the Victron is another Blue Light...

[charliem]

[font size="3"]Leslie,

I will also add my cautions on total discharge. Dealers sound like thy are knowledgeable, but seldom are. I refer you to Battery University at: [a href="http://batteryuniversity.com/learn/article/absorbent_glass_mat_agm"]http://batteryuniversity.com/learn/article/absorbent_glass_mat_agm[/a]  .

A key quote from the article is:

"The leading advantages of AGM are a charge that is up to five times faster than the flooded version, and the ability to deep cycle. AGM offers a depth-of-discharge of 80 percent; the flooded, on the other hand, is specified at 50 percent DoD to attain the same cycle life."

80% discharge, not 100%. The note on faster recharge is also true for AGMs, but only if the charging system can support it. Generally not true for TVs with 7 pin connectors.
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[david]

Ok, here is some techie/geeky stuff:

I once measured 7 amps of charge coming from my TV's connector when the batteries were down but not that down, maybe down 30%. Since batteries take more voltage to charge at the same current the more they get charged, a 50% discharged battery might take 13V to charge at 20 amps of current. But as Charlie notes the TV/Trailer is wired with 10 gauge wire, so there is a very significant voltage drop at 20 amps, about a volt. Since the TV's alternator will only put out about 13.5 volts, there is not enough voltage at the battery terminals- 13.5-1 = 12.5 to supply 20 amps. So it supplies less and the voltage drop is less and it balances, maybe a 10 amps.

So, due to the fixed voltage of the alternator and the voltage drop in the wire, a 90% discharged battery (not a good idea, even with an AGM) might see 20 amps as you start charging. As it reaches 50% it might see 10 amps and at 20% it will probably be down to less than 5 amps.

The bigger wire in the jumper cable helps a lot with the voltage drop as Charlie noted, but does nothing for the fixed output voltage of the alternator. It might take several hours of TV charging with a jumper cable to add 100 amp hours to a pair of 50% discharged golf cart batteries.

Finally, you have to wait a long time to use the voltage vs state of charge charts accurately, at least 4 hours of total resting- no loads and no charging. This was proved by another very geeky boater friend who measured his battery voltage every hour for 24 hours. It didn't begin to stabilize until after 4 hours and dropped another tenth of a volt at 12 hours. A tenth of a volt difference is approximately 10% SOC difference and at after only an hour it was off three tenths of a volt or 30%..

David