How long to charge batteries on 30amp service?

**sande005** · 02-18-2023, 09:38 PM

Some good information already given. In my experience, with two 6v LA batteries and the stock converter...if run way lower than one should (like to 20% or even less), it can take a long time for the stock converter to charge them back up. The converter is not high end, and is designed around recharging a single 12 v, usually a group 27. So the dealer was not wrong in the standard case. But, you have more than doubled the available amp hours by going to 2 6v, so while maybe not twice as long, still will take in that range. With other things drawing power during charging, the process can then slow down to be longer.
On those few times I have run my 2-6 way down, it can take two days, or a bit more, to get fully back to 100%. I'd say all is normal, just give it time.

BTW - you have roughly 200AH total capacity. Common advice is to avoid going below 50% for longest life, but these are made to discharge deeper, so not as critical as a stock 12v. But it still is much better to be nice to them. The point is that even with 2 100 AH lithium, you aren't gaining a big margin of additional capacity. You can drive them deeper all the time, but the total is still about the same as if you were being "bad" to the 2 6v.

Without going crazy on the lithium purchase, you might consider 200 AH of lithium, a new converter that can charge them at a higher rate, and/or increasing the solar (for those extended off grid stays).

**Riverbug** · 02-19-2023, 06:31 AM

Originally Posted by Derekm

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?

Thanks for the help everyone!

No problem charging our battery overnight but we didn't have that battery long before we switched to lithium. However, even with the lithium battery and the OEM converter/charger, it didn't have to run all night to get to it's usual charge level (which is lower than what lithium likes). I'd check your batteries again for state of health (not state of charge) after you potentially drew them down quite a bit. If still no issue with the batteries then you might want to get the converter/charger checked. There certainly are instances of those going bad, but much more reliable these days than the ones we had years ago. Good luck!

**Big Blue** · 02-19-2023, 07:08 AM

A good battery monitor.."I like Renogy" would answer all your questions.... It would tell you amp use when boondocking , and amps charging rate when you have hook ups.... By isolating 12v users in your camper and doing a little math, you can figure out how many amp hour batteries you need.....

**DougW9876** · 02-19-2023, 07:37 AM

To answer your question about if the converter is working; turn off the solar charger and disconnect from shore power. Check the voltage at the battery and make note of it. Plug in to shore power and check the voltage at the battery again, if the converter is providing charge current the voltage will be higher. The actual voltage numbers will depend on the state of charge of the batteries so this is just a quick test to see if the converter is working.

**Derekm** · 02-19-2023, 08:18 AM

Originally Posted by xrated

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

Thanks I will give that a try this morning. Just so I am clear you are not suggesting I disconnect the battery, correct? And you want me to measure voltage at the converter, I assume that is in the breaker/fuse panel in the trailer and then measure at the battery to compare. I assume I will need to pull the panel out to get that reading?

As a quick update I put the external charger on last night to see what condition it thought the battery was in and it read 70%. I was plugged in to 30amp service. I did not leave the external charger on overnight. This morning I checked it again and the external charger said it said thet the battery was in worse shape (60%) despite being plugged in all night.

Thanks for the discussion

**xrated** · 02-19-2023, 10:52 AM

Originally Posted by Derekm

Thanks I will give that a try this morning. Just so I am clear you are not suggesting I disconnect the battery, correct? And you want me to measure voltage at the converter, I assume that is in the breaker/fuse panel in the trailer and then measure at the battery to compare. I assume I will need to pull the panel out to get that reading?

As a quick update I put the external charger on last night to see what condition it thought the battery was in and it read 70%. I was plugged in to 30amp service. I did not leave the external charger on overnight. This morning I checked it again and the external charger said it said thet the battery was in worse shape (60%) despite being plugged in all night.

Thanks for the discussion

Correct, what you are looking for with my test described in my post #4 , is a voltage drop from the converter leads to the actual battery terminals. The only way to see if there is a significant voltage drop (which would be a problem) is to have the battery connected and the converter/charger (CC) trying to charge the battery.....in other words WITH current flowing to the battery. In my case, I had 6 1/2 to 7 tenths of a volt drop from the converter output to the battery terminals. I know that doesn't sound like much, but look at the reality of it. On LiFePO batteries, 3.45 volts per cell is considered to be fully charged...or so close that it's not worth talking about. 3.45V per cell equals 13.8V for the entire battery. Let's say the charger is putting out 14.2V.....but because of bad connections, wire size too small, circuit resistance added in via bad connections/cheap connectors, etc....the battery is only receiving 13.6 or 13.5 volts at the terminals. That battery will never fully charge, in that scenario.

And if you can get to the actual CC, that is where you want to take your readings from...the actual pos and neg lead coming off of the CC. And then the next reading at the actual battery terminal posts....the pos. and the neg. posts...ALL done while current is flowing and the battery is charging. If you find a voltage drop of one or two tenths of a volt, that's not too bad. But if you find 5....6...7...tenths...maybe more, that is something that needs to be fixed in order to get the charging voltage up high enough to fully charge a battery.

One other suggestion for you. Take all of your readings with the SAME meter. Using different ones can result in different readings/numbers taken at the same place. Even if the meter is off just a bit, if you use the same one for all of your measurements, it will be consistent all the way through. In checking for voltage drop, it's not so much about what the actual voltage SHOULD be, it's more about determining how much voltage drop there is from point A to point B.....and in this case, it's from the CC to the battery terminals. Hope this helps.

**Derekm** · 02-19-2023, 07:33 PM

Originally Posted by xrated

And if you can get to the actual CC, that is where you want to take your readings from...the actual pos and neg lead coming off of the CC. And then the next reading at the actual battery terminal posts....the pos. and the neg. posts...ALL done while current is flowing and the battery is charging. If you find a voltage drop of one or two tenths of a volt, that's not too bad. But if you find 5....6...7...tenths...maybe more, that is something that needs to be fixed in order to get the charging voltage up high enough to fully charge a battery.

I ran the test and at the CC it reads 12.94V, at the battery terminals it reads 12.89V. Note that I was by an Autozone today and just for the heck of it I had the batteries tested again (3rd time in 2 weeks) and once again they told me that the batteries were in good shape. I am camped in a new campground near Tuscon, fortunately we have power again so I have my external charged hooked up to top up the batteries.

Derek

**twinwashbrewing** · 02-22-2023, 02:40 PM

Originally Posted by 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

I did not see where any one asked what the stages of charge from your on board converter are? You could be on 1000 amp service and it will only charge what the output of the converter is. I had an older converter that just charged at 1amp hour. I suggest upgrading your converter to one that has several stages. It can sense the need on the battery and will hit it with more amps and then move into a float/maintain stage.

**SolarPoweredRV** · 02-22-2023, 03:09 PM

Originally Posted by twinwashbrewing

I did not see where any one asked what the stages of charge from your on board converter are? You could be on 1000 amp service and it will only charge what the output of the converter is. I had an older converter that just charged at 1amp hour. I suggest upgrading your converter to one that has several stages. It can sense the need on the battery and will hit it with more amps and then move into a float/maintain stage.

With Lithium Batteries, you don't need multiple charging stages because they can accept a charge at such a high rate. A good Lithium Capable Converter is what is needed. I recommend looking at the Progressive Dynamics line of Lithium Converters. You would probably want a Converter capable of charging at an 80 to 90 amp rate.

**lfytsmith** · 02-22-2023, 06:57 PM

Something that might affect your charging is the solar charger. If your converter/charger sees that voltage, it may think it is your batteries and drop to float voltage charge. I installed an inexpensive voltage meter and found that my charger is two stage and once it is "happy" with the voltage level of the batteries it drops from bulk to float and takes forever to fully charge my two 12v batteries. I would find out what converter/charger you have and what the specs are for it. You can find the model number on GD webpage for your make, year, model.