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Old 11-06-2019, 10:00 AM   #1
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Faster Coach Battery Charging from Genny?

I recently purchased two Duracell Ultra Platinum AGM Deep Cycle batteries (92 amp each) for my coach and after a night of boon-docking running off DC power (with a 100% charge) they are down to maybe 75-80% come morning. (CPAP must really drain battery.)

The problem is that it seems to take 1 1/2 to 2 1/2 hours of genny time to bring the battery back up to full charge...that's sometimes a challenge based on our schedules and park rules.

It's too late for me to switch batteries to a Lithium solution so are there any tricks or adapters I can add that speed the charging process up? Thanks!
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Old 11-06-2019, 10:10 AM   #2
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Solar would help.
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Old 11-06-2019, 11:34 AM   #3
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Move the charger so that it's as close to the batteries as you can get. I saw a huge increase in performance and less taper off when I moved my charger so that it was within 3' of the batteries vs. 20' away.
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Old 11-06-2019, 11:44 AM   #4
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Solar would help.
I do have 100 watts of solar using a Renogy portable panel. Definitely better if you're in a site with nice direct sun...though I realize they still get some charge from in-direct sunlight too.
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Old 11-06-2019, 11:45 AM   #5
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Move the charger so that it's as close to the batteries as you can get. I saw a huge increase in performance and less taper off when I moved my charger so that it was within 3' of the batteries vs. 20' away.
Wow...great tip...I'll pursue that change...thanks!
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Old 11-06-2019, 11:50 AM   #6
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Move the charger so that it's as close to the batteries as you can get. I saw a huge increase in performance and less taper off when I moved my charger so that it was within 3' of the batteries vs. 20' away.
Absolutely a good way to improve charging.

If for any reason it's not possible to move the converter/charger closer to the batteries due to lack of space an alternative is to replace the Positive wire that connects converter in it's current location to the batteries. Negative connections on each end are typically to the chassis and those shorter runs should be replaced too.

Use the heaviest gauge wire that the converter's lug will accept. Before I changed to Lithium batteries I did this in my TT, replacing the factory's #8 awg wire with #4. Made a significant change in the amount of voltage drop from converter to batteries. In retrospect I wish I'd gone with #2 awg so i'd recommend the largest that will fit in the lugs.

A good source of wire at reasonable prices is Amazon. I used welding cable and it's offered in various pre-cut lengths, even in pairs of red and black.
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Old 11-06-2019, 11:57 AM   #7
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Use the heaviest gauge wire that the converter's lug will accept. Before I changed to Lithium batteries I did this in my TT, replacing the factory's #8 awg wire with #4. Made a significant change in the amount of voltage drop from converter to batteries. In retrospect I wish I'd gone with #2 awg so i'd recommend the largest that will fit in the lugs.
I bought #2 AWG cables for my converter as it advertised being able to use the such. The hole on the converter for the battery was nowhere near big enough. I had to trim down strands so it would ultimately fit.
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Old 11-06-2019, 12:06 PM   #8
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I bought #2 AWG cables for my converter as it advertised being able to use the such. The hole on the converter for the battery was nowhere near big enough. I had to trim down strands so it would ultimately fit.
I had the same problem with one lug but found one of these on Amazon:



https://www.amazon.com/KnuKonceptz-O...qid=1573059770
Cutting out a few strands works too but this is a more neater and stronger approach.
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Old 11-06-2019, 12:19 PM   #9
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Cutting out a few strands works too but this is a more neater and stronger approach.
Oh that's cool! I like it. I might pickup a pair of these and trim back my wires.
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Old 11-06-2019, 12:21 PM   #10
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If you haven't already done it, try turning off the heated humidifier on the CPAP...that sucks a lot of power.
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Old 11-06-2019, 12:55 PM   #11
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Oh that's cool! I like it. I might pickup a pair of these and trim back my wires.
Just remember that they do add some RIGID length to the wire so make sure you have clearance and can still make any bends in the wire that may be necessary.
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Old 11-06-2019, 12:55 PM   #12
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If you haven't already done it, try turning off the heated humidifier on the CPAP...that sucks a lot of power.
Thanks for mentioning this but I'm just running the "blower" only to not suck anymore DC power than it already is...but I miss my nice warm air humidifier!

I considered buying a dedicated "travel battery" that is sold by the CPAP places...it would get me through the night but then I've still got the challenge of getting it charged back up for the next night.

Boon-docking gets you into some great parks but I sure miss that shore power!
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Old 11-06-2019, 01:05 PM   #13
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Another option is to add a 2nd charge line running back to the battery from the converter/charger.

Most units come with 6ga from the factory and the battery is often 20' or more from the converter/charger. Adding a 2nd 6ga line reduces the line loss due to the distance. If you can't move the converter closer, adding a thicker gauge wire or doubling the lines both will reduce the line loss and decrease charge time some (increases amperage capable of being delivered to the battery).

Most converter/chargers are part of the AC & DC distribution panel and difficult if not impossible to move, so it's easier to double the charge line or increase the wire gauge to #4 or #2. I went with #2 gauge on mine to upgrade from the factory #6 which ran a good 30' back to the battery on a 55 amp converter/charger.

Also before you order those adapters from Amazon like Titan Mike showed, make sure you have space for them at the connection point as it will add length to the wire before it can start to turn. But those lugs are the correct way to connect thicker wire to a terminal that is a too small, rather than trimming some strands off the wire.

-------------------------------------
Edit
One other thought... Is your CPAP running off an DC to AC inverter or does it have a DC power plug option? You do loose some "power" as overhead for a DC to AC converter and the smaller ones like 300-500 watts are usually less efficient than the larger more expensive sine wave inverters. So that may contribute to the drain. See if they make a DC plug power cord for your model as that may help.

Also you still have phantom DC loads in the trailer and if you ran the furnace, that is a DC power hog for sure when the fan runs.
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Old 11-06-2019, 01:06 PM   #14
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TitanMike and ependydad...I'm hoping my converter is already very close to the batteries...under my frig, inches from the breaker box, and the entry steps where my batteries are located. If that's the case, then it's just a matter of changing out wiring to the heaviest gauge possible as you mentioned. Is that just needed from converter to battery or also from converter to breaker box connection too? (I am very much an electrical novice.) Thanks!
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Old 11-06-2019, 01:22 PM   #15
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Most converter/chargers are part of the AC & DC distribution panel and difficult if not impossible to move, so it's easier to double the charge line or increase the wire gauge to #4 or #2.
Good call. I was introduced to this concept with my new rig. I simply added a second converter close to the batteries. I reused the circuit breaker for the original. I just un-wired it and wired in a new outlet for the new converter.
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Old 11-06-2019, 01:23 PM   #16
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Makes you wonder...

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Originally Posted by TitanMike View Post
Absolutely a good way to improve charging.

If for any reason it's not possible to move the converter/charger closer to the batteries due to lack of space an alternative is to replace the Positive wire that connects converter in it's current location to the batteries. Negative connections on each end are typically to the chassis and those shorter runs should be replaced too.

Use the heaviest gauge wire that the converter's lug will accept. Before I changed to Lithium batteries I did this in my TT, replacing the factory's #8 awg wire with #4. Made a significant change in the amount of voltage drop from converter to batteries. In retrospect I wish I'd gone with #2 awg so i'd recommend the largest that will fit in the lugs.

A good source of wire at reasonable prices is Amazon. I used welding cable and it's offered in various pre-cut lengths, even in pairs of red and black.
Makes you wonder why the converter manufacturers don't make a four-wire connection to the batteries. The technique has been around for decades. It would add less than a buck to the cost of the converter.

The sense circuit (regulates the voltage out) connects to the batteries along with the charge cables, instead of connecting internally at the converter end. These are high impedance, so they can be fine wire, e.g., AWG 22. The "switching mode too early" problem completely goes away.

I've ranted about this before and the response is deafening silence.
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Old 11-06-2019, 01:35 PM   #17
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Makes you wonder why the converter manufacturers don't make a four-wire connection to the batteries. The technique has been around for decades. It would add less than a buck to the cost of the converter.

The sense circuit (regulates the voltage out) connects to the batteries along with the charge cables, instead of connecting internally at the converter end. These are high impedance, so they can be fine wire, e.g., AWG 22. The "switching mode too early" problem completely goes away.

I've ranted about this before and the response is deafening silence.
I've always wondered the same thing. My Solar Controller receives it's control voltage readings from my battery monitor (both Victron) and disregards any voltage drop between battery and controller when determining which "mode" to use while charging.

I've even asked the people at Progressive Dynamics and didn't really get an answer.

I believe their answer is to merely recommend floor mounted Converters (like 9100/9200 series) that can be mounted next to the batteries and merely plugged into and AC outlet nearby.

If I were to install a Victron Converter it too would share battery voltage with the Victron network. Charging would be controlled by the voltage read at the battery by the shunt.
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Old 11-06-2019, 01:42 PM   #18
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TitanMike and ependydad...I'm hoping my converter is already very close to the batteries...under my frig, inches from the breaker box, and the entry steps where my batteries are located. If that's the case, then it's just a matter of changing out wiring to the heaviest gauge possible as you mentioned. Is that just needed from converter to battery or also from converter to breaker box connection too? (I am very much an electrical novice.) Thanks!
Not necessary to change wire from converter to breaker box connection as long as the converter is mounted in the power center. The short wire between the two has little resistance compared to the long run from converter to battery. That wire is more appropriately sized for the current drawn through the fuse board than for battery charging at a distance.
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Old 11-06-2019, 01:59 PM   #19
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"One other thought... Is your CPAP running off an DC to AC inverter or does it have a DC power plug option? You do loose some "power" as overhead for a DC to AC converter and the smaller ones like 300-500 watts are usually less efficient than the larger more expensive sine wave inverters. So that may contribute to the drain. See if they make a DC plug power cord for your model as that may help.

Also you still have phantom DC loads in the trailer and if you ran the furnace, that is a DC power hog for sure when the fan runs."

dward51, based on past great input from this forum I did get a DC cord for my CPAP which plugs into a cig outlet close to my bed. And those phantom loads (with everything off) are a bigger issue than most know. Even with my battery cut-off engaged, I lost 15% battery power over the course of two weeks with it in storage. Have now charged it up and disconnected negative cables to stop that!
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Old 11-06-2019, 02:03 PM   #20
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Sorry, but 100 watts of solar isn't much, but since every bit helps here is a tip.

A solar panel may lose over 50% of it's charging capability if it is dirty.

Dirty doesn't mean covered with mud. Dirty with >50% loss means just a little dust or condensation spots.

Second tip is to use alagator clips and short cables between your portable charger and your batteries. If you use the 'solar ready' connection you my lose up to 25% of your input due to line loss. The same applies if you are using a 12v extension cord.

Third tip: Check your solar controller to verify th amps of input you are getting out of it. My 100W Dokio panel produces less than half the amps of my 110W Zamp suitcase charger. Zamp is expensive. Dokio is cheap. You get what you pay for.

I connect my Dokio and my Zamp directly to the batteries. On a good day, they will maintain the charge on the batteries when I'm using only the on-board loads (lights, water pump, etc., with nothing else plugged in or running).
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