Charging Choice

[ClimberRob]

In all these scenarios, wouldn't the same current be flowing through the positive wire to the camper battery, and therefore be protected by the circuit breakers on that wire? The only reason you would need a separate breaker on the negative would be in the case where you could have an (excessive) current flowing on the negative wire which is not also flowing on the positive wire. I can't think of any scenarios where this would be the case.

Not trying to be argumentative here, but trying to make sure we are giving good advice. A breaker on the negative for a dual battery is not something I have ever run across before, so I want to make sure it actually serves a purpose and that I am not missing something.

It's OK if you don't get it. "We" are not giving advice. I'm giving my advice, and you're giving yours. You are, indeed, being argumentative. Stating that you're "not trying to be" doesn't have any effect on that. That's OK, too.

 

[ClimberRob]

A lead- acid battery's internal resistance will self limit the max actual charge rate. They're not super-capacitors. No knowledge if you're using one of the more advanced chemistry batteries.

Unfortunately, that's not how it works. You will fry a FLA battery by pushing too many amps into it.

 

[ntsqd]

That's odd because that is what I was taught, repeatedly, in Auto Repair classes.

 

[docalex]

I am no expert .....
I recently installed renogy 40 amp dc to dc charger.
I butchered a pair of 4awg jumper cables to run wire from the truck to the charger and battery in my truck bed next to my camper. There is a 50 amp inline fuse and cut off switch under the hood. The charger needs another 12 volt signal that activates a built in relay switch to turn the unit on. I wired a switch into the cab of my truck. I have a battery monitor installed on my system. Now please understand I JUST installed this system, so this is not advice coming from experience. The system, when turned on, charges the battery at 40 amps then ramps down to 20 and finally a 2 amp trickle... It seems to work well and fast.

My only regret is that I did not buy the 20 amp model... I recently acquired a lifepo4 battery that can only take 20 amps max. Looking for a solution ...

here is a link to video from my "lectric" Guru

Ps...

I installed this battery monitor... I cant imagine running my system without it.

 

[JaSAn]

Unfortunately, that's not how it works. You will fry a FLA battery by pushing too many amps into it.

That is how my 2 GC2s (6V FLA) work.

I charge with a 35 amp adjustable battery charger (adjustable voltage). My depleted batteries will accept max current as the voltage climbs to set voltage (for my batteries = 14.3V), then amps drop until battery will not take any more (~ 2 amp = 100% charged).

If the voltage is set too high (higher than manufacturers recommended bulk charge rate) I will boil my batteries and loose fluid quickly.
At the correct or lower voltage it would take months to loose enough fluid to damage the batteries.

Batteries are 5 Y.O. and still going strong.

 

[Vic Harder]

Unfortunately, that's not how it works. You will fry a FLA battery by pushing too many amps into it.

i think my Rolls batteries in my previous camper could accept a 1C charge rate. they were 275AH. i don’t think many alternators are likely to fry FLA batteries

 

[alano]

Update on my charging choice (re-hijacking my thread ): I used 4 AWG welding wire and shortened the path from about 30 feet to just under 15 feet. Went with the Renogy 40amp DC/DC charger. On test drive after letting camper batteries get down to 12.3 volts with no load (lost the percent of full charge when rewiring the battery box I managed to trip the breaker) I got over 30 amps for a bit but then it settled to 24 amps as the voltage rose to something over 13.

Probably would have been happy with the 20amp DC/DC charger and saved some coin. Sooner or later really low batteries and a short driving day will make this one pay off I suspect. I used a low voltage protection circuit https://www.amazon.com/gp/product/B07929Y5SZ/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1 to control the DC/DC converter so as to provide the same sort of extra protection to the truck battery that an isolator gives. I need to tune turn on and off voltages a little as things were bouncing early in the test drive. I also ran a control wire from the ignition back through the trolling motor connector in case this protection circuit proves problematic.

I considered a manual switch, but I am terrified that I would forget to turn it off without some sort alarm or knock on the head.

Thanks to all who offered advice. Pulling wire for the truck only took an hour or so although wiring up the battery box and securing everything back there took much longer. I had to take the camper off the truck to install the trolling motor connector, but a friend wanted to move a bed this past weekend so I had extra incentive to be a good friend and get the project going.

Alan

 

[Vic Harder]

sounds like a good fit for you!

 

[ClimberRob]

That's odd because that is what I was taught, repeatedly, in Auto Repair classes.

Batteries are specced with a max charge current. As Vic stated below you, many batteries can accept a 1C charge. That's not the same as self-regulating. For a 275AH battery, as in Vic's, or your, example, with a 1C charge rate, it's unlikely to be an issue. If someone hooks up a 35AH battery to their big diesel truck alternator, it's very likely to be a problem.

That is how my 2 GC2s (6V FLA) work.

I charge with a 35 amp adjustable battery charger (adjustable voltage). My depleted batteries will accept max current as the voltage climbs to set voltage (for my batteries = 14.3V), then amps drop until battery will not take any more (~ 2 amp = 100% charged).

If the voltage is set too high (higher than manufacturers recommended bulk charge rate) I will boil my batteries and loose fluid quickly.
At the correct or lower voltage it would take months to loose enough fluid to damage the batteries.

Batteries are 5 Y.O. and still going strong.

A 35 amp charger is charging those batteries very gently.

 

[ClimberRob]

Update on my charging choice (re-hijacking my thread ): I used 4 AWG welding wire and shortened the path from about 30 feet to just under 15 feet. Went with the Renogy 40amp DC/DC charger. On test drive after letting camper batteries get down to 12.3 volts with no load (lost the percent of full charge when rewiring the battery box I managed to trip the breaker) I got over 30 amps for a bit but then it settled to 24 amps as the voltage rose to something over 13.

Probably would have been happy with the 20amp DC/DC charger and saved some coin. Sooner or later really low batteries and a short driving day will make this one pay off I suspect. I used a low voltage protection circuit https://www.amazon.com/gp/product/B07929Y5SZ/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1 to control the DC/DC converter so as to provide the same sort of extra protection to the truck battery that an isolator gives. I need to tune turn on and off voltages a little as things were bouncing early in the test drive. I also ran a control wire from the ignition back through the trolling motor connector in case this protection circuit proves problematic.

I considered a manual switch, but I am terrified that I would forget to turn it off without some sort alarm or knock on the head.

Thanks to all who offered advice. Pulling wire for the truck only took an hour or so although wiring up the battery box and securing everything back there took much longer. I had to take the camper off the truck to install the trolling motor connector, but a friend wanted to move a bed this past weekend so I had extra incentive to be a good friend and get the project going.

Alan

Nice!

 

[ckent323]

I found the following information which may be of use relative to battery charging

https://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

https://www.itacanet.org/eng/elec/battery/battery.pdf

https://www.impactbattery.com/blog/2017/05/how-fast-can-i-charge-my-car-battery/

https://www.powerstream.com/SLA.htm



Relative to Lifeline Batteries I found the following:

"The charging current during bulk charging should be set as high as practical; higher current levels mean faster recharge time and less time for the plates to become sulfated. Due to the low impedance design, Lifeline batteries can tolerate an inrush current as high as 5C (500 A for a 100 Ah battery)."

I do not believe this is unique to Lifeline batteries but it may only apply to high quality batteries - I don't really know.

Ref: http://lifelinebatteries.com/wp-content/uploads/2015/12/6-0101-Rev-E-Lifeline-Technical-Manual.pdf


Note: internal resistance in a lead acid battery changes with SOC and temperature.

https://batteryuniversity.com/learn/archive/how_does_internal_resistance_affect_performance

and

https://batteryuniversity.com/learn/article/rising_internal_resistance

I hope this information is helpful.

Regards,

Craig

 

[radarcontact]

Sounds like this thread is winding down, as Alan did some rewiring and improved his charging. Just wanted to throw in my recent experience w/charging, in case anyone else is considering charging alternatives.

I recently replaced my original Surepower 1314A separator with a Blue Sea 7611 ACR. When the separator was in place I would notice, after camping at night and driving the next day, that it would take a long time to bring the batteries up to full charge when the engine was running. I have a hefty solar panel bank on my Hawk roof (320W), so charging the camper batteries is not usually a big concern for me, but the slowness of charging when driving, on a cloudy day, bugged me. I attributed this to the separator not connecting when camper batteries were in the mid 12V or lower range. Anyway, I thought the 7611 ACR would be a simple and inexpensive experiment. I left all my original camper wiring the same, i.e., 10 AWG. Since replacing the separator w/the ACR I've noticed a significant improvement in charging. If, for example, I wake up one morning after camping and my batteries are, say, 82-85% capacity, which is typical for my usage, and my battery voltage is around 12.4-12.5, I can start my engine and the amperage going into the batteries is usually over 10A initially, according to my battery monitor (I've seen it as high as 15-16A). It will gradually drop off as the batteries become fully charged. Happens much faster than with the separator. After driving for an hour or two everything is 100%, and my camper batteries are in float mode.

So, just swapping the separator with the ACR and making no other changes did improve things for me. Plus, I now can keep my engine battery topped off w/solar, since the ACR joins the two battery banks and acts as one. Of course, having heavier gauge wire would improve charging even more, but at this point I don't really feel I need it.

 

[So Cal Adventurer]

Excellent Info here! I am getting ready to upgrade all of my wiring as well!

Thanks