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Old 11-07-2022, 10:47 PM   #1
wchoe
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Default Low voltage on RV batteries

I have a 24ft Gulfstream Mini Vista Cruiser Class B+, with three 12v deep-cycle lead-acid batteries totaling 310Ah. One older Interstate, and 2 EverStart batteries which are a year old. Lately, the voltage drops below 11v, even though only 25% of capacity is used in 1-day. The remaining voltages of the individual batteries do vary due to the way they're hooked up. Have tested them with battery analyzer and load-tester which says they're good. I use them mainly for lights, water-pump, e-bike, laptop, phone.

The RV converter charges at a constant 13.4v when hooked to shore-power. Also have a DC-to-DC charger which does multi-stage charging when driving. Wonder whether the different ages and capacity of the batteries, is causing this problem.

Please let me know if anyone knows why this may be happening.

Thanks
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Old 11-08-2022, 01:04 AM   #2
NavyLCDR
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Originally Posted by wchoe View Post
Please let me know if anyone knows why this may be happening.

Thanks
Likely the different ages and capacities of the batteries.
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Old 11-08-2022, 11:50 AM   #3
Chuck v
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Agree...it is very unlikely you can charge parallel batteries of different ages and manufacturers to full capacity -- nor will they provide a good discharge performance.


Further, the float charge voltage of your batteries should be at least 13.8 to 14 volts, and an equalizing charge should be provided periodically.


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Old 11-08-2022, 02:47 PM   #4
NavyLCDR
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Further, the float charge voltage of your batteries should be at least 13.8 to 14 volts, and an equalizing charge should be provided periodically.


Chuck
Very wrong. Float (trickle) charging for lead-acid and AGM deep cycle batteries should be 13.2 - 13.4 volts. At least that is what the two largest converter manufacturers (WFCO and Pressive Dynamics) set it at.

14.4 is boost and equalizing charging to quickly get the batteries up to 80%

13.4 to 13.8 is normal charging to get batteries from 80 to 100%

Float or trickle charging a fully charged battery is at 13.2 to 13.4 volts.
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Old 11-09-2022, 10:30 AM   #5
Chuck v
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Navy,


You are correct, and I meant to say the "absorption" voltage needs to be 13.8 to 14.5 volts as seen in the description and graph below. The real key to "float" is to keep the current into the battery at less than 1% of battery capacity to limit electrolyte loss... Your voltage ranges quoted above are very good examples of the voltages involved in the various stages.



Note also that the bulk stage on two stage chargers ends at the higher voltage of the absorption/equalization range of 13.8 to 14 volts for flooded lead acid cells and sealed lead acid types (red and green traces on the chart...) Some older RV chargers are two stage units.
Bulk

The Bulk stage is where the battery receives the majority of its energy, making up about 80% of the recharge cycle. During this stage the Battery is given as much current as possible while keeping the battery temperature under 100 F.

Absorption

A 3 Stage Controller adds an Absorption phase (Sometimes called an “Equalization Stage”) that other “Smart Chargers” don’t include. During this stage the controller will maintain the target charging Voltage (Between 14.1VDC and 14.8VDC), while decreasing the charging Amperage. This helps retain the energy stored during the Bulk stage.

Float

Keeping a battery topped off once it is fully charged is a big part of getting the most out of SLA Batteries. The Float stage does exactly that by reducing the input Voltage to between 13VDC and 13.8VDC, and the Current to less than 1% of the Battery Capacity. This will keep a battery fully charged indefinitely.
Thanks for correcting my earlier terminology error!


Chuck
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File Type: jpg 12 volt battery charge voltages and cycles.jpg (54.9 KB, 1 views)
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Old 11-10-2022, 11:44 PM   #6
wchoe
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Thanks for the responses.

The Converter charger is an IntelliPower 9100 which provides a constant 13.6V charge. (don't have the Charge Wizard which does 3-stage charging)

I will switch the batteries to only use the 2 year-old EverStart 105Ah batteries, which are hooked up in parallel.

If this setup doesn't solve the low-voltage problem, I will look into upgrading to Lithium batteries, but will need to also change the Converter charger.
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Old 11-13-2022, 01:50 PM   #7
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Default Upgrade time?

When you replace the batteries, consider upgrading to LiPO4 since you don't have the little multistage Dongle (which seemed overpriced to me). I replaced my charger with a Victron unit and a smart shunt, and put in a pair of 300 amp hour Chins cells with BMI built in. I can go ten days off grid running pump, lights refrigerator control (propane for the fire), and charging phones computers, running the tv off the inverter...fans. no worries. The Bly tooth app for the shunt monitors battery state. Recharge the whole capacity in less than 6 hours. No water to check. Beautiful.
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Old 11-13-2022, 03:36 PM   #8
Chuck v
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Freed,


Sounds like a great way to start over and get a fully updated system -- what did it all cost you?? 300 amp hour batteries are quite large capacity...what is their physical size?


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Old 11-14-2022, 10:38 AM   #9
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Freed,


Sounds like a great way to start over and get a fully updated system -- what did it all cost you?? 300 amp hour batteries are quite large capacity...what is their physical size?


Chuck
Batteries were these:
2 PCS 12V 300Ah LiFePO4 Deep... https://www.amazon.com/dp/B08N5TGTPW?ref=ppx_pop_mob_ap_share

Charger:
Victron Energy Skylla-IP65... https://www.amazon.com/dp/B08MP9LX8H?ref=ppx_pop_mob_ap_share

Smart shunt:
Victron Energy SmartShunt 500 amp... https://www.amazon.com/dp/B0856PHNLX?ref=ppx_pop_mob_ap_share

Plus cables, bus bars, battery rack that I made to replace the stock battery mounts. I mounted the batteries & charger in the bay where the transfer switch and power cord are located on my supernova. Still have room to store the cord and the fresh water hose in there. Not a great storage setup in these from the factory. Nit designed by actual camping folks...
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Old 11-14-2022, 11:21 AM   #10
Chuck v
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Freed,


So...about $4,000 or so in parts plus your modifications in the mounting, etc. for this house battery bank conversion.



I lived in my coach full time for several years and spent about $2,000 during that time maintaining and replacing all three battery banks (not just the house bank...) so if I were to keep the coach and full time in it for a decade I might reach cost parity. Convenience and confidence parity would happen much sooner, perhaps...


Thanks for the information!


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Old 11-14-2022, 12:54 PM   #11
wchoe
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Thanks for the upgrade recommendations.

The existing Intellipower charger is in a tight-space below the Fridge, so need to check on access to upgrade, and also existing connections to generator and shore-power, via a transfer switch.
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Old 11-15-2022, 06:46 AM   #12
FreedMeister
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Default Expensive upgrade

Yes, it was not an inexpensive upgrade, but it got the existing charger out if a tight spot, took the heat of it out if the cabin, and increased my usable stored electrical power by a lot. The faster recharge time is great when running the generator for power. Solar will be the next adventure, but not on this rig. I do plan to take the upgraded charging/battery system off and transfer it to the new rig too. RV work is not for the thin wallet, that we all know.
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