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Old 05-26-2021, 07:18 PM   #1
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battery charging

Hi all.
I'm plugged into 110V.
I get 13V out of the trailer leads going to the batteries.
the batteries are at 5V and need to be charged.
when I connect the leads to the batteries the voltage drops to 5V and the batteries will not charge. the same happens when I hitch up.
thanks for helping
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Old 05-27-2021, 02:13 PM   #2
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I would try connecting your leads to another battery and see if the voltage also drops. Obviously, it will only drop as low as the resting battery voltage but if lower than the 13v you see when not connected then your converter is probably bad.

It’s odd that the tow vehicle won’t charge the battery either because that should avoid the converter all together as it your tow vehicle is a 12 volt system and should bypass the converter.

Lastly, you might try pulling the trailer battery out and trying to charge with another 12v charger and see off you can get it to fully charge.

Good luck.
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Old 05-27-2021, 02:53 PM   #3
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How old are the batteries? Maybe it is time to change them if they read 5v...
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Old 05-27-2021, 03:27 PM   #4
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done all that. it may be a loos on a corroded connection.
buttery is not old.
My friend - electrition by trad - will help next week.
the leads have 13V telling me the converter is working. the voltage drops when i connect it to the batters.
going on a trip today so maybe the car will charge it.
thank y'all
stay well
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Old 05-27-2021, 04:02 PM   #5
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Battery Charging Voltage Profile

The typical battery charging voltage profile starts at the voltage level of the battery. So in this case it should start a 5.0 volts.

The converter/charger supplies all the current the battery will absorb up to the chargers capacity limit. As the charge continues, the batteries absorb less and less current. The voltage slowly raises to the chargers predetermined voltage limit. The limit will be 13.3, 13.6 or 14.4 volts.

It takes 14 to 18 hours to fully charge lead acid batteries. However, voltage should reach the predetermined charger limit in about 4 hours depending on the charger capacity. Small capacity chargers take longer to bring the voltage up.

Continue charging for the full 14 to 18 hours for a full clean charge.

If the voltage does not slowly raise from 5.0 volts there are many possible causes.
  1. Charger may detect low starting voltage and stop charging altogether. It assumes the battery is defective and will not charge. Charge using a portable automotive charger until voltage reaches 11.4 volts.
  2. Battery may be defective and not accepting charge.
  3. Charger may be defective and not able to supply rated charge current.
  4. Water level in battery may be extremely low. Bring water level up to top of plates (not to full level). Level will rise when charging. Recheck level after 14 hours of charging. Fill to full level.

I wish you good luck and happy trails ahead!
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Old 05-28-2021, 03:58 PM   #6
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5V reading on the battery? I would say that battery is completely toast and needs replacing. I don't think it can be recovered. Even if it isn't old, a battery left connected to a trailer in storage will drain due to parasitic loads on the 12V system (propane detector, some CO detectors, stereo clocks, other 12V accessories in a standby mode, etc). Drain it too low and it becomes permanently damaged, even if it was brand new and bursting full of charge to start with.

The 13V reading on the converter output sounds good like it is performing as expected. It is odd that you don't get the same reading at the battery, it is possible the connection between converter and batteries is broken.
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Old 05-28-2021, 07:17 PM   #7
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Quote:
Originally Posted by ewarnerusa View Post
5V reading on the battery? I would say that battery is completely toast and needs replacing. I don't think it can be recovered. Even if it isn't old, a battery left connected to a trailer in storage will drain due to parasitic loads on the 12V system (propane detector, some CO detectors, stereo clocks, other 12V accessories in a standby mode, etc). Drain it too low and it becomes permanently damaged, even if it was brand new and bursting full of charge to start with.

The 13V reading on the converter output sounds good like it is performing as expected. It is odd that you don't get the same reading at the battery, it is possible the connection between converter and batteries is broken.
Nearly correct.

When a lead acid battery is discharged, it dissolves lead from one set of plates, converts it to lead sulfate (or something close) and deposits it on the other set of plates.

Drawing the battery down to 5 volts may or may not dissolve some of the supporting structure. Deep draw batteries are resistant to this type of damage depending on how they are designed and built.

However, leaving the battery discharged for a long period can cause permanent damage. The lead sulfate slowly crystalizes. The crystals are difficult to redissolve by charging. Large crystals may fall off the plates before recharging or may require persistent recharge voltage to get them to recharge.

Permanent loss of capacity is the result. This has nothing to do with how old the batteries are.

AGM type lead acid batteries are more resistant to this type of damage. The chemistry runs out of chemical in the electrolyte before structural damage can occur. The pads between the electrodes hold the lead sulfate crystals in place until they are recharged. Large crystals can still resist recharging.

I wish you good luck and happy trails ahead!
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Old 05-30-2021, 12:47 PM   #8
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although I left the batteries connected over the winter, I have also left them connected to AC.
I have another set of batteries that gave me the same results. So it is most likely a loose connection. I did not want to take things apart just before a trip and risking a bigger problem. I'm camping now with shore power.
will dig into it next week when I'm back at home.
I shall keep you all posted.
thanks
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Old 05-30-2021, 05:25 PM   #9
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If you leave a constant charge on the batteries for a long time you will kill them. All the water will very slowly boil out and you will be done. You need a float charger that cuts off when the batteries are full or you need to stop charging them for periods of time.
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Old 05-30-2021, 08:16 PM   #10
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thanks for the info, I guess this coming winter they go in the garage.
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Old 06-02-2021, 03:13 PM   #11
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Originally Posted by dsol View Post
If you leave a constant charge on the batteries for a long time you will kill them. All the water will very slowly boil out and you will be done. You need a float charger that cuts off when the batteries are full or you need to stop charging them for periods of time.
You do not need to remove batteries to store, if rig is plugged into shore power.

Most modern RV battery chargers hold a constant voltage suitable for storage of flooded cell batteries. If you have not altered the charging parameters, 3 months should be fine.

Monitor the water level until you know how much water your rig will consume. Much used batteries may use more water.

My WFCO will drop charge voltage to 13.2 volts automatically after about 4 days if steady, low current (storage conditions).

Next time you put your rig into storage while plugged in to shore power, come back a week later and check the battery terminal voltage. 13.2 volts is ideal for storage. 13.6 is OK but a bit high for many AGM batteries.

Lower than 12.7 volts is probably means the batteries are disconnected. It is Ok for flooded cell batteries for a couple of months. Check voltage and do a full 10 hour recharge before voltage drops to 12.4 volts.

Battery University https://batteryuniversity.com/

How does the Lead Acid Battery Work? https://batteryuniversity.com/learn/...ased_batteries

Charging lead acid batteries https://batteryuniversity.com/learn/...d_acid_battery

AGM https://batteryuniversity.com/learn/..._glass_mat_agm

How to Charge and When to Charge? https://batteryuniversity.com/learn/...o_charge_table

How to Store Batteries https://batteryuniversity.com/learn/...tore_batteries

Summary of Do’s and Don’ts https://batteryuniversity.com/learn/..._battery_table

How to Measure State-of-charge
https://batteryuniversity.com/learn/...tate_of_charge
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Old 06-02-2021, 05:02 PM   #12
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My Batteries are seald
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Old 06-02-2021, 07:38 PM   #13
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new info.
I connected the batteries directly to the car with jumper cables, it was charging nicely and keeping the charge.
I was checking the leads going to the batteries from the trailer. they are a bit corroded, suddenly things started working, but not for long.
the lead was getting hot and at some point, I heard a relay click and it stopped charging, removed the connection, heard the relay reset and it started again. there is a connection box on the outside of the trailer, is there a relay there?
any idea what to expect before I start removing things?
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Old 06-02-2021, 09:27 PM   #14
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Jumper cables from engine to house battery terminals would have no box or other electricals. What happens to the house battery terminal voltage when jumpers are connected?

I assume the trailer was still connected through the 7 pin connector at the hitch. In this case there is usually a self resetting circuit breaker.

My Dutchman Kodiak Cub has a 30 amp self resetting breaker between the hitch and the battery. Next is an electrical connector box. The box has no electronics inside. It only has wire connections.

So you may be experiencing high current from tow vehicle to trailer battery. Breaker trips do to over current and when it cools off, it resets.

The high current may be due to a short inside the battery which would also account for the low voltage at the battery terminals as well as wires getting hot and circuit breaker tripping.

In the case of an internal short, the battery has failed and cannot be recovered.
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Old 06-02-2021, 09:38 PM   #15
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The jumper cables were connected directly to the battery, the seven PIN connector was not connected. With this setup, the battery is charging and holding the charge.
I have other batteries so tomorrow I will try to hook it up to a fresh battery and see if I get the same results.
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Old 06-02-2021, 10:01 PM   #16
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To enable more discussion:

Is it two 12v batteries in parallel? Two 6v batteries in series?

Are they wet or AGM? Deep draw, marine type?

What instrument are you using to test for V?

What voltage do your batteries read when disconnected from both shore power and your truck?

What does each battery read when isolated, disconnected from trailer and each other?

What is the amperage coming from the converter when the leads are not connected to the batteries?

What is the amperage rating of the converter?
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Old 06-02-2021, 11:34 PM   #17
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2 12V in parallel,
dry cell
using Volt meeter.
I read 3 V when not connected, was 2 before jumping it for 5 Min.
did not ck the batters individually
did not chk the amps
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Old 06-05-2021, 03:33 PM   #18
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battery disconnect

Once you get the batteries replaced or charged install one of these on the negative cable. (need to get another cable). This keeps the battery from discharging while sitting. If you store it for months then take out the battery and put on a trickle charger .
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Old 06-06-2021, 02:33 AM   #19
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Update, and perhaps a conclusion. As it turned out, one of the cables was corroded and did not make good connections. As I was playing with it, it made the connection and I started getting thirteen 1/2 volts when connected to the batteries. However, by then both batteries were damaged. Perhaps a short inside they will not charge. The cables were getting hot in the relay, kept on clicking and stopping the charge. I replaced the batteries. And all seems to be working nicely so far. Thank you all for all the help. And yes, I have a kill switch.
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