How long to charge batteries on 30amp service?

[Derekm]

I have a 22MLE with 2 x 6v batteries, I was boondocking for 2 days and now am at an RV park with full hookups. I plugged in yesterday at 4pm, it is now 17 hours later. I was told by a grand designs tech that being plugged in to 30amp service overnight should top up the batteries. However I just put a battery charger on them and they are showing 60%. Is that normal or should the converter in the trailer have topped up the batteries in that time? The batteries were not depleted after boondocking, everything was still working. Thanks

[Soundsailor]

I have a 22MLE with 2 x 6v batteries, I was boondocking for 2 days and now am at an RV park with full hookups. I plugged in yesterday at 4pm, it is now 17 hours later. I was told by a grand designs tech that being plugged in to 30amp service overnight should top up the batteries. However I just put a battery charger on them and they are showing 60%. Is that normal or should the converter in the trailer have topped up the batteries in that time? The batteries were not depleted after boondocking, everything was still working. Thanks

So a few points here. Assuming your batteries are lead acid, one factor might be the age of the batteries, LA batteries charge slower as they age (don't we all). A second consideration is what other loads were being met by your converter/charger as the batteries were charging. Third, what was the actual state of charge at the beginning of the charging cycle? Finally, what is the charging capacity of your charger?

[Derekm]

Thanks for your reply. They are lead acid, about 1 year old. They have been tested twice, once by the dealer and once at autozone. Both said they are in good condition. Minimal other loads, 12v fridge and a bit of furnace. I can’t say exactly what the state was at the beginning of the charge cycle but the meter in the trailer said good and everything including the fridge and furnace were working fine on battery alone. The tech was confident that the converter in the trailer should easily have topped up the batteries overnight but that doesnt seem to be the case and wondering if others agree with him. Wondering if I have a problem with my converter. Btw I previously disconnected solar and disconnected the battery and put a volt meter on the lead from the trailer and got 13v so it would seem thet the converter was working?

[xrated]

There are many factors that affect the charging of a battery and how long it takes to charge them...and I'll try to cover them here. Battery age, battery capacity in Amp Hours, type of battery chemistry, converter/charger output voltage, other items on the 12V system being used at the same time (using some of the power that would be going to charge the battery), actual voltage AT the battery terminals (could be suffering some voltage drop between the converter/charger and the battery at various connection points) and even the temperature. So as you can see, lots of different possibilities

Probably the first place I would start is to try and bring the battery back to about the same level of charge it was at when you tried to charge them. Then, try to remember what all you have turned on and running (12VDC stuff). Next, use a decent multimeter and take a voltage reading at the terminals of the converter/charger...write it down. Then move over to the battery itself and take a voltage reading directly on the battery terminals themselves......write it down. If you have a meter that will display 1/10ths of a volt, pay close attention to the difference between the voltage at the converter/charger, and what is actually arriving at the battery. You will have some voltage drop if the charger is actually working at charging the battery. A static system, with nothing 12V turn on or in use and the battery not charging, will not show much, if any, voltage drop. The lower the battery's state of charge is, the more current it should pull when charging. If you only have a meter that just shows voltage without the numbers in tenths or hundredths of volts, you probably aren't going to see any difference between the converter/charger and the battery terminals.

[Soundsailor]

Thanks for your reply. They are lead acid, about 1 year old. They have been tested twice, once by the dealer and once at autozone. Both said they are in good condition. Minimal other loads, 12v fridge and a bit of furnace. I can’t say exactly what the state was at the beginning of the charge cycle but the meter in the trailer said good and everything including the fridge and furnace were working fine on battery alone. The tech was confident that the converter in the trailer should easily have topped up the batteries overnight but that doesnt seem to be the case and wondering if others agree with him. Wondering if I have a problem with my converter. Btw I previously disconnected solar and disconnected the battery and put a volt meter on the lead from the trailer and got 13v so it would seem thet the converter was working?

You don't say which coach you have, but you do mention a 12-volt refrigerator. They can draw a lot of power when off-grid, two days powering a 12-volt refer could easily have left the batteries with very little charge left. That would have required a longer charge time. The "meter" in the trailer is pretty useless, best to disconnect the battery, let it rest for an hour or so, and then measure the charge with your volt meter. That will give you a much better idea of what you're working with.

[jkwilson]

I have a 22MLE with 2 x 6v batteries, I was boondocking for 2 days and now am at an RV park with full hookups. I plugged in yesterday at 4pm, it is now 17 hours later. I was told by a grand designs tech that being plugged in to 30amp service overnight should top up the batteries. However I just put a battery charger on them and they are showing 60%. Is that normal or should the converter in the trailer have topped up the batteries in that time? The batteries were not depleted after boondocking, everything was still working. Thanks

How does the battery charger know how much capacity the batteries have? The only thing the charger can do is monitor current. If you didn’t disconnect the batteries from the trailer, the charger was supplying a good portion of the trailer with power in addition to the batteries.

[EsquireRV]

You don't say which coach you have, but you do mention a 12-volt refrigerator. They can draw a lot of power when off-grid, two days powering a 12-volt refer could easily have left the batteries with very little charge left. That would have required a longer charge time. The "meter" in the trailer is pretty useless, best to disconnect the battery, let it rest for an hour or so, and then measure the charge with your volt meter. That will give you a much better idea of what you're working with.

@Derekm ‘s original post shows it’s a 22MLE. But you’re absolutely correct that using a volt meter to read battery charge requires a disconnected battery. Otherwise you’re measuring other loads and aren’t getting a true reading.


This trailer has a 10cu ft fridge that uses approx 1.08kwh /day (varies with time of year, location, etc.)
Given 2 days of boondocking, that ends up pretty close to:
1.08kwh/12V DC *1000 = 90 Amp hours per day (x2) result in 180Amp hours just in fridge use. For most 6V lead acid batteries, this means your running them way below 50% State of Charge. If you boondock multiple days very often, you’d be best to fix the 12V battery situation (Lithium).

Drawing down the batteries below 50% will dramatically reduce their useable life.

[SolarPoweredRV]

@Derekm ‘s original post shows it’s a 22MLE. But you’re absolutely correct that using a volt meter to read battery charge requires a disconnected battery. Otherwise you’re measuring other loads and aren’t getting a true reading.


This trailer has a 10cu ft fridge that uses approx 1.08kwh /day (varies with time of year, location, etc.)
Given 2 days of boondocking, that ends up pretty close to:
1.08kwh/12V DC *1000 = 90 Amp hours per day (x2) result in 180Amp hours just in fridge use. For most 6V lead acid batteries, this means your running them way below 50% State of Charge. If you boondock multiple days very often, you’d be best to fix the 12V battery situation (Lithium).

Drawing down the batteries below 50% will dramatically reduce their useable life.

I agree with the above.

I would like to add that it is possible that you damaged your batteries and that is why they aren't charging.

Test the batteries after another day of charging and see if things are better.

By-the-way, it looks like you are headed for a couple of upgrades to your Electrical System...

Lithium batteries

Higher Amperage Lithium Capable Converter.

Keep us posted on what you find out.

[Derekm]

Only thing to add here is that the trailer comes stock with a 165W solar panel and the sun was shining while we were boondocking so it should have been adding some charge back… the batteries have been checked twice in the last 2 weeks and both times they were showing to be in good condition…but getting back to my original question, my external charger seems to top up the batteries in 4-5 hours. Grand design tech told me that the internal converter should easily top up the batteries overnight. Assuming the batteries are not damaged (because they have been tested and there is no indication they are bad) are other peoples batteries get recharged overnight when plugged in to 30Amp service, or do I need to keep bringing my battery charger? Just trying to figure out if there is something wrong with my internal converter.

I am also realizing how completely useless the battery meter is on the inside control panel of the trailer.

Thanks for the help everyone!

[xrated]

Only thing to add here is that the trailer comes stock with a 165W solar panel and the sun was shining while we were boondocking so it should have been adding some charge back… the batteries have been checked twice in the last 2 weeks and both times they were showing to be in good condition…but getting back to my original question, my external charger seems to top up the batteries in 4-5 hours. Grand design tech told me that the internal converter should easily top up the batteries overnight. Assuming the batteries are not damaged (because they have been tested and there is no indication they are bad) are other peoples batteries get recharged overnight when plugged in to 30Amp service, or do I need to keep bringing my battery charger? Just trying to figure out if there is something wrong with my internal converter.

I am also realizing how completely useless the battery meter is on the inside control panel of the trailer.

Thanks for the help everyone!

See my post number 4....I gave you a good place to start. Then let me/us know what you found.