How much converter/charger is really needed?

Bobbo wrote:

BFL13 wrote:
Not answered by the OP is the post in another thread where he said he can't get through one night with his current battery bank with the furnace running at a decent temperature, so they freeze under many blankets. the usual rule is one night per battery and he has two.

So that must mean his batteries are already shot, and need replacing now unless he is not going off grid for a while.

Sigh. You are fixated on my batteries. I am not focusing right now on my batteries. I am focusing on whether I should go to the trouble of pulling out my 45 amp charger and replacing it with a 55 amp charger. Will the answer to that question change depending on whether the batteries are good or not? I have not answered about the batteries until now because that is not my focus. I will not answer about my batteries again after this. If and when I become concerned about my batteries, I will do something about them. I don't know about your furnace fan, but my furnace fan, running all night, tends to take a lot of battery power. With only 158 a-h of battery power, it isn't hard to run them down to 50% SOC on a very cold night with the furnace running non-stop. We have found a solution that works for us.

NinerBikes wrote:
My solution... find another heater, that doesn't require electricity and your batteries all night.... there is stuff out there that runs on propane and a cracked vent and a cracked window for proper ventilation.


Olympic Wave 3 or Wave 6.

Please note that this thread is not about discharging my batteries. This thread is not about heating my RV. This thread is only about whether I would gain enough in recharging discharged batteries to justify replacing a 45 amp charger with a 55 amp charger. The way the batteries get discharged is immaterial.

unless you need every second of generator time to get charged back up before running out of time, and your wiring supports the 55amp model.

there is nothing gained other then time, and even then it will be a small amount. you have to decide if the time savings is worth it to you, that's about all your gonna gain, in bulk mode

BFL13 wrote:
My ugly graph says that on a 220AH bank starting at 50%, the time difference is about 18 minutes from 50-75% and it is the same times after 75%

So you will save about 18 minutes of gen time doing a 50-80 or 50-90 (75-100 same times, so no advantage past 75% SOC.) by choosing a 60 over a 45 on 220AH.

Now, THIS is extremely useful information. Going from a 45 amp unit to a 55 amp unit saves me about 18 minutes of charge time. I consider that negligible over a 4 hour +/- runtime. Thank you.

MEXICOWANDERER wrote:
At what voltage sir? Starting with maximum absorbsion voltage of 14.8 and continuing?

I get out the 2000 watt Honda when my solar control panel shows 12.0v to 12.1v first thing in the morning. I don't think my PD4645V does 14.8v, it does 14.4v. Thank you for addressing the topic rather than worrying about heating the RV or replacing the batteries.

BFL13 wrote:
Not answered by the OP is the post in another thread where he said he can't get through one night with his current battery bank with the furnace running at a decent temperature, so they freeze under many blankets. the usual rule is one night per battery and he has two.

So that must mean his batteries are already shot, and need replacing now unless he is not going off grid for a while.

Sigh. You are fixated on my batteries. I am not focusing right now on my batteries. I am focusing on whether I should go to the trouble of pulling out my 45 amp charger and replacing it with a 55 amp charger. Will the answer to that question change depending on whether the batteries are good or not? I have not answered about the batteries until now because that is not my focus. I will not answer about my batteries again after this. If and when I become concerned about my batteries, I will do something about them. I don't know about your furnace fan, but my furnace fan, running all night, tends to take a lot of battery power. With only 158 a-h of battery power, it isn't hard to run them down to 50% SOC on a very cold night with the furnace running non-stop. We have found a solution that works for us.

NinerBikes wrote:
My solution... find another heater, that doesn't require electricity and your batteries all night.... there is stuff out there that runs on propane and a cracked vent and a cracked window for proper ventilation.


Olympic Wave 3 or Wave 6.

Please note that this thread is not about discharging my batteries. This thread is not about heating my RV. This thread is only about whether I would gain enough in recharging discharged batteries to justify replacing a 45 amp charger with a 55 amp charger. The way the batteries get discharged is immaterial.

My solution... find another heater, that doesn't require electricity and your batteries all night.... there is stuff out there that runs on propane and a cracked vent and a cracked window for proper ventilation.


Olympic Wave 3 or Wave 6.

MEXICOWANDERER wrote:
At what voltage sir? Starting with maximum absorbsion voltage of 14.8 and continuing?

Based on the charger at 14.6 and holding with no drop till batteries charged right up. However, the amps taper at a lower battery voltage than the 14.6 due to voltage drop while still at higher amps.

You only get the 14.6 at the batteries when amps have tapered right down.

At what voltage sir? Starting with maximum absorbsion voltage of 14.8 and continuing?

My ugly graph says that on a 220AH bank starting at 50%, the time difference is about 18 minutes from 50-75% and it is the same times after 75%

So you will save about 18 minutes of gen time doing a 50-80 or 50-90 (75-100 same times, so no advantage past 75% SOC.) by choosing a 60 over a 45 on 220AH.

Whether there is any point in saving that 18 minutes of gen time each time you do a 50-90 depends on how often you do it in a year, how much gasoline costs, what the gen hours are at the campground, how hard is it to get more gas, etc.

Not answered by the OP is the post in another thread where he said he can't get through one night with his current battery bank with the furnace running at a decent temperature, so they freeze under many blankets. the usual rule is one night per battery and he has two.

So that must mean his batteries are already shot, and need replacing now unless he is not going off grid for a while.

MEXICOWANDERER wrote:
If you went from 45 amps to the point of saturation charging of GC 220 batteries you may find they accept almost 100 amperes when starting out at a 50% depth of discharge.

The advice I give about saturation charging must remain in context. It is designed to reduce generator run time to a minimum. There is a heck of a difference between runtime of a Harbor Freight 2-cycle 800 watt generator charging a single group 24 RV battery and a 6,500 watt generator running to charge the same battery. A 45 ampere converter will max absorbsion voltages but the battery calls the shots. X number of minutes to go from 50% SOC to 90% SOC.

500 amperes at 28.9 volts is a lot of va. But the balance of horsepower versus saturated absorbsion charge of the batteries is entirely valid.

Lbs of fuel per hour vs kWh is not linear at low draws. It short a 6.5 generator is a FUEL HOG when powering a 500 watt load. It is just plain nuts to try charging a 400 ampere hour bank with a 45 ampere converter and six thousand watt generator.

On public power the 45 amp makes perfect sense. Off grid the 45 amp charger is a fuel spendthrift.

Mex, I know you mean well and think you are completely understandable. However, I can't translate what you just wrote into currently having a pair of Marine/RV batteries with a 158 a-h rating and a 45 amp converter on a 2000 watt Honda generator. Then upgrading the batteries, later, to a pair of 225 a-h batteries still keeping the 2000 watt Honda. Do I need to keep the 45 amp charger, or go to the 55 amp charger?

If you went from 45 amps to the point of saturation charging of GC 220 batteries you may find they accept almost 100 amperes when starting out at a 50% depth of discharge.

The advice I give about saturation charging must remain in context. It is designed to reduce generator run time to a minimum. There is a heck of a difference between runtime of a Harbor Freight 2-cycle 800 watt generator charging a single group 24 RV battery and a 6,500 watt generator running to charge the same battery. A 45 ampere converter will max absorbsion voltages but the battery calls the shots. X number of minutes to go from 50% SOC to 90% SOC.

500 amperes at 28.9 volts is a lot of va. But the balance of horsepower versus saturated absorbsion charge of the batteries is entirely valid.

Lbs of fuel per hour vs kWh is not linear at low draws. It short a 6.5 generator is a FUEL HOG when powering a 500 watt load. It is just plain nuts to try charging a 400 ampere hour bank with a 45 ampere converter and six thousand watt generator.

On public power the 45 amp makes perfect sense. Off grid the 45 amp charger is a fuel spendthrift.

OP here. My take on this, as a practical matter, is stay with the 45 amp unit and don't go over 225 a-h if and when I replace the batteries.

I have 2 6V-GC's, I went from a PD9245 to PD9260; I doubt I saw over 45A charging more than 10 hours in many years of use. I doubt it was worth the upgrade. Since you have the PD4645 now, I'd just be happy with it; if you were buying new, I'd get the 60.