Journey with Confidence RV GPS App RV Trip Planner RV LIFE Campground Reviews RV Maintenance Take a Speed Test Free 7 Day Trial ×
 


Reply
 
Thread Tools Search this Thread Display Modes
 
Old 01-17-2022, 10:05 AM   #1
Winnebago Camper
 
Join Date: Oct 2021
Posts: 38
Running engine vs generator to charge batteries

We mostly boondock when we camp and rely on our generator and/or starting the engine to recharge our coach batteries. Solar panels may be the way to go eventually but for now just wondering what the opinion is on the best of our two current methods to charge the coach batteries. Which is better, run the generator for 1-2 hours or run the engine for 20 minutes. We try not to let the batteries run below 12.2 and running the engine seems to get our batteries back up to 12.8 for 4-5 hours with minimum lights and such. Running the generator and same light usage seems to last through the day but both the engine and generator use gas to run. Which uses more gas and/or is better to run?
dennysbabe is offline   Reply With Quote
Old 01-17-2022, 11:51 AM   #2
Winnebago Master
 
Join Date: Feb 2020
Posts: 880
Sounds like both charging sources are charging at about the same rate. Hard to say which source will use less fuel. The generator has to run at 3,600 rpm and that burns fuel even with no load. I assume you are running the chassis engine at idle when you are charging. That may actually use less fuel at 700 rpm or so even though it is a much, much bigger engine and has lots of bearings to keep turning.

My guess is that the chassis engine burns less fuel than the generator. But it could go the other way.
__________________
2021 Thor Axis 24.1
DavidM is offline   Reply With Quote
Old 01-17-2022, 12:34 PM   #3
Winnebago Owner
 
Join Date: Jun 2020
Posts: 70
Charging battery

A lot depends on your alternator size. Also every time you start the engine they say it takes about 7 miles of driving to recharge the chassis battery. Running the generator is what itís made to do. Not using it has other problems. It would be interesting to see how many amps both batteries are getting. Maybe someone will chime in for more information. Travato John
TravatoJohn is offline   Reply With Quote
Old 01-17-2022, 01:55 PM   #4
Winnebago Camper
 
Join Date: Dec 2021
Location: Casa Grande, AZ
Posts: 7
I would run the generator. That's what it is for, and what it is designed to do. Running the engine at idle for 20 minutes probably will not get the oil hot enough to expel moisture, so over time you could build up contaminants in the oil... not a good thing.
SalE is offline   Reply With Quote
Old 01-17-2022, 06:01 PM   #5
Site Team
 
creativepart's Avatar
 
Join Date: Sep 2009
Location: Spring Branch, TX
Posts: 5,514
Idling your motorhome engine for 20 mins is not ideal. I’d use the generator. Here’s a thought, find out what rate your Converter’s charger is charging at and replace it with a charger section that charges at a higher rate.

The charger is separate from the rest of the converter and you can replace it fairly easily and they don’t cost a ton of money. Plenty of YouTube videos on doing this job.

When driving your RV the alternator is a good way to charge your batteries, but when dry camping the generator is the go to charging source.
__________________
2017 Winnebago Adventurer 37F
2016 Lincoln MKX Toad
creativepart is offline   Reply With Quote
Old 01-23-2022, 05:08 PM   #6
Winnebago Camper
 
Join Date: Jan 2022
Posts: 6
Use your chassis engine to charge your batteries!

I rent out motorhomes and have had 30 different motorhomes over the years. I recommend renters run their chassis engine to charge their camper batteries because your engine will have between 200 and 300 amp alternator, versus probably only about 50 amps coming from the onboard converter. So they will charge much faster then using your generator.
Plus in many parks they don't allow you to run your generator (national parks), or they have very limited hours when you can do so. But there is no rule against running your engine (which is typically quieter than your generator anyways), and you would only have to run the engine for a half an hour versus several hours on the generator for the same charge..
For the same reasons above, I have never bothered to upgrade a motorhome to very expensive solar systems or lithium batteries. Running the RVs engine for a few minutes a day should keep your camper batteries topped off when boondocking.
Dave
DavesRVs is offline   Reply With Quote
Old 01-23-2022, 05:46 PM   #7
Winnebago Camper
 
Join Date: Jan 2022
Posts: 6
@MadMaxWinny said "Unless you've got an extremely large alternator (130+ amp) and a sophisticated (non-stock) voltage regulator, 20 minutes of engine battery charging won't get you much."

The reality is that both the Ford E450 and MB Sprinters chassis' come with at least a 210A alternator. (I just double checked on Winnebago's website). That alternator is designed to charge BOTH the engine battery and camper battery(s) via the Aux batt charge relay found in most motorhomes.
In contrast, most Class C RV converters are only 50A, and much of that is going to your camper's other 12vdc needs.
DavesRVs is offline   Reply With Quote
Old 01-23-2022, 06:41 PM   #8
Site Team
 
creativepart's Avatar
 
Join Date: Sep 2009
Location: Spring Branch, TX
Posts: 5,514
DavesRV, what works for a rental fleet may not apply not to what RV owners find works best. When you own your RV upgrading batteries, adding solar, updating converters all make perfect sense. Idling the RV with jack warnings beeping, etc not so much.
__________________
2017 Winnebago Adventurer 37F
2016 Lincoln MKX Toad
creativepart is offline   Reply With Quote
Old 01-23-2022, 07:01 PM   #9
Winnebago Owner
 
Join Date: Aug 2020
Posts: 140
There is still the issue of voltage regulation (I have no idea how it is handled). Boats pretty much follow automotive equipment, and I'd be surprised if RVs were any better. A stock voltage regulator won't give you a very good charge algorithm, in fact, you are lucky to see anywhere near half of the rated current at the batteries (and often at the wrong voltage).
__________________
2002 Winnebago Brave (WPF32V)
Workhorse P32
S/N 10F71C261406
MadMaxWinny is offline   Reply With Quote
Old 01-23-2022, 07:10 PM   #10
Winnebago Camper
 
Join Date: Jan 2022
Posts: 6
I agree, voltage regulation is important. Newer model Chassis' (Ford E450 and MB Sprinters) do vary the charging voltage, which should work fine for the RV batteries as well. (Older engine alternators just put out a constant 14v, which over-charges the batteries).

The cheap 12vdc converters they install in motorhomes also typically charge at one voltage, say 13.5v or so. Lead-acid and AGM batteries should ideally have a four stage converter/charger, with 4 different voltages and currents depending on the charge state of the battery. I have replaced many converters with a "smart" 100A 4-stage converter for this reason alone: to lengthen the life of my batteries. (Note: A different converter is required if you are going with lithium batteries, you can't just "drop in" 2 $1000 lithium batteries in place of your AGM or lead acid batteries but that is a whole 'nuther topic)

BTW, another good benefit of charging at a high rate of current (i.e >50A, from the engine alternator) occasionally is that this removes the "sulfation" that accumulates on the plates of lead acid batteries that are all to often drained below 11.5v. This is often the cause of short battery life. A good quality $125 27 or 29 series lead acid battery that is properly charged, maintained, and never frozen should easily last 5 years or more.
DavesRVs is offline   Reply With Quote
Old 01-23-2022, 07:41 PM   #11
Winnebago Owner
 
Join Date: Aug 2020
Posts: 140
Well, you are close. I cannot speak for newer RVs, but most I've encountered have basically automotive charge programs. 14V is fine for most batteries in the bulk/absorption stage (it's actually a bit low for most). It's the float stage that gets a bit tricky. Any sealed battery is going to have pretty specific needs (although AGM is very close to flooded, close enough that I make no alternator voltage adjustments in my cars/truck/RV/boat).

I would agree that most RV chargers I've encountered are pretty much 30+ year old technology and should be replaced (adding an inverter is the perfect time).

As far as sulfation charging is concerned, this is accomplished with high voltage, not current. You can't "push" current into a battery, just like you can't force more water through a pipe. A battery takes what its internal resistance will allow.
__________________
2002 Winnebago Brave (WPF32V)
Workhorse P32
S/N 10F71C261406
MadMaxWinny is offline   Reply With Quote
Old 01-24-2022, 06:47 AM   #12
Winnebago Owner
 
Join Date: Sep 2020
Posts: 107
With my 2004 Itasca Meridian 34H, I did some evaluation of battery charge options, and will attempt to share my findings. I did not keep the detailed data, because the situation was easy to understand and generalize.

My propulsion engine is a Cat 7 330hp, with about 80K on it, and the genset is an Onan 7500, with about 500 hours on it. Both run well, and have no known issues.

The Cat 7 feeds some data to a Freightliner monitor, and I have installed a Scanguage D, to better monitor fuel burn.

I became familiar with the engine alternator as it failed about 20% into my trip bringing the rig home after I bought it. It is a conventional alternator, commonly used in RVs and is rated at 160A. When the propulsion engine runs, the alternator charges both the chassis and the coach batteries.

Understand that an alternator is not the best way to charge a battery. Smart chargers are much better, but few RVs utilize them, and an alternator is certainly the most conventional charging method.

I did not use a clamp on current meter in my evaluation, but I may at some time.

Here's what I came up with. When cold the idle of the Cat 7 burns several gallons of diesel per hour. As the engine warms up, that fuel burn lowers, but it is always well over 1 GPH.

In contrast, the genset burns a max of 0.96 GPH. The output is 120V, 62.5A, and will automatically match the power setting to provide for the power demand. For me, the charging circuit is the inverter/battery charger combo on the rig. While that charger may not be as efficient as a Smart Charger, it is smart enough to taper the charge, and from a time efficiency standpoint, it will charge at a max charge rate when the batteries are low.

So basically, the fuel burned by the generator will never exceed that of my idling propulsion engine. And the power available to charge the coach batteries will always be high, and controlled by the inverter/charger.

For the Onan 7500, the fuel burn is:

Idle: 0.13 gal/hr
50% 0.49 gal/hr
100% 0.96 gal/hr

So from a fuel perspective, the genset is less fuel per unit time.

From a charge efficacy standpoint, charging through the inverter/charger is presumed to be equal or better than using the engine alternator.

The hourly maintenance and wear and tear costs on the genset is less than on the propulsion engine. Furthermore, the alternator I replaced at about 80k miles was the third on the rig. From what I can find, replacing the engine alternator every 40k is not uncommon.

I realize this does not have allot of hard data, and may not be well written, but bottom line is that costs are less and charging is likely faster using the genset to charge the batteries.

One downside. On my rig, the genset does not charge the chassis/propulsion starting batteries. That can be accomplished two easy ways. A previous owner installed a chassis battery charger that can be activated to keep the chassis battery topped off. Or, the battery boost switch can be jammed into the continuously on position, which is not ideal, but bridges both sets of batteries together. The contactor is rated for continuous on, but again, this is not the ideal way to charge batteries. Nor is the propulsion alternator.
__________________
2004 Itasca Meridian
Cat 7 330hp rated
Mongobird is offline   Reply With Quote
Old 01-24-2022, 06:59 AM   #13
Winnebago Camper
 
Join Date: Jan 2022
Posts: 6
I agree it takes higher voltage (up to 25v?) to overcome the overcome the internal resistance of a sulfated battery. I am a BSEE (Automotive Electrical Engineer actually) by day, but the "BatteryGuy" can explain it better than me :-)
https://batteryguy.com/kb/knowledge-...portant-facts/

One more thing, then I'll stop playing the geek: I have replaced the cheap Cole Hersee battery isolator / charging relays on many RVs when they fail with a 'smart' "Voltage Sensing Relay" (VSR - https://www.amazon.com/dp/B00400IYTK), which charges bi-directionally.

For example, for folks who normally leave the RV plugged into shore power for months (i.e at a campground or winter storage like me), this relay will turn on when the camper batteries reach full charge and then charge the engine battery. No need for a separate "battery tender" for the engine battery.
Likewise, if the engine is running, and the engine battery is low, it will charge only the engine battery, and then turn on to charge the camper battery.
I've been using this for years and it has prolonged the life of both batteries significantly.
I wish the RV OEMs would install these at the factory.
Dave
DavesRVs is offline   Reply With Quote
Old 01-24-2022, 07:34 AM   #14
Winnebago Owner
 
Join Date: Aug 2020
Posts: 140
Nice summary, Mongo! There is a very easy way to link the chassis battery when charging. Get a "Battery Combiner" which allows a small portion of the house charge to divert to the chassis battery when it detects charging voltage. It then disconnects when the voltage drops (both values are user adjustable on most quality units).
__________________
2002 Winnebago Brave (WPF32V)
Workhorse P32
S/N 10F71C261406
MadMaxWinny is offline   Reply With Quote
Old 01-24-2022, 08:03 AM   #15
Winnebago Owner
 
Join Date: Sep 2020
Posts: 107
Quote:
Originally Posted by MadMaxWinny View Post
Nice summary, Mongo! There is a very easy way to link the chassis battery when charging. Get a "Battery Combiner" which allows a small portion of the house charge to divert to the chassis battery when it detects charging voltage. It then disconnects when the voltage drops (both values are user adjustable on most quality units).
So is the combiner tricked by solar generation? What is the current capacity? And does it manage the charge, so that current is higher on a low battery, and trickle levels on a nearly charged battery?

For optimum charging of batteries, a Smart Charger can manage the current, the voltage, the temperature, etc.

But the OP question was about efficiency of charging with engine vs genset, in terms of fuel.

With all that said, I am disappointed that better solutions are not more universally available, which manage the charge state, the charge and intelligently select the power source.
__________________
2004 Itasca Meridian
Cat 7 330hp rated
Mongobird is offline   Reply With Quote
Old 01-24-2022, 08:09 AM   #16
Winnebago Master
 
Join Date: Nov 2018
Location: Pflugerville/Austin, Tx
Posts: 4,350
Quote:
Originally Posted by dennysbabe View Post
We mostly boondock when we camp and rely on our generator and/or starting the engine to recharge our coach batteries. Solar panels may be the way to go eventually but for now just wondering what the opinion is on the best of our two current methods to charge the coach batteries. Which is better, run the generator for 1-2 hours or run the engine for 20 minutes. We try not to let the batteries run below 12.2 and running the engine seems to get our batteries back up to 12.8 for 4-5 hours with minimum lights and such. Running the generator and same light usage seems to last through the day but both the engine and generator use gas to run. Which uses more gas and/or is better to run?
Lots of stuff thrown in and some not very logical, so perhaps look at it from a simple angle?

When you run the genrator, it does one thing, it generates electricity!

When you run the RV engine it does lots of things like generate power but also runs the other equipment that is hung on the enginee. You are running power steering, Air conditioning, etc. that is not being used.

So do you want to put wear and tear on things the engine uses so that things like oil, filters, spark plugs and any other moving parts need wear out faster or do you want to just put wear on a generator that is designed for what you want done?

Which is more expensive to replace, the generator or the RV engine?

When I want to slice an apple, I use a knife, when I trim a hedge I use a hedge trimmer but I only use a chain saw when I want to cut something big!

If boondocking long enough to feel the start batttery may have run down, a simple strap between the positive of the coach and positive of the start will charge the start when running the generator, if there has not been any other provisions made. Since very little current will be carried a wire as small as a number 10 with clips on the end is handy and plenty big for the charging current. Do remove the strap when not charging if you want to avoid the possibility of runningboth stes down!
__________________
Richard
Morich is offline   Reply With Quote
Old 01-24-2022, 08:46 AM   #17
Site Team
 
creativepart's Avatar
 
Join Date: Sep 2009
Location: Spring Branch, TX
Posts: 5,514
Quote:
Originally Posted by DavesRVs View Post
I wish the RV OEMs would install these at the factory.
Dave
Winnebago does on just about all new motorhomes and has done so since at least 2017, if not earlier.

They use a different brand than you mentioned. But it does the same thing and keeps both house and chassis batteries fully charged when on shore power or generator. The F53 alternator charges both banks when driving and the OEM inverter/charger has a very capable 80amp smart charger for FLA, AGM and LFP batteries.
__________________
2017 Winnebago Adventurer 37F
2016 Lincoln MKX Toad
creativepart is offline   Reply With Quote
Old 01-24-2022, 08:53 AM   #18
Winnebago Owner
 
Join Date: Aug 2020
Posts: 140
Quote:
Originally Posted by Mongobird View Post
So is the combiner tricked by solar generation? What is the current capacity? And does it manage the charge, so that current is higher on a low battery, and trickle levels on a nearly charged battery?
The combiners simply sit between the house and chassis batteries. Depending on the size rating (and wire gauge) they allow a smaller portion of the current to divert to the chassis bank (which is usually all that is required). They are not "smart," per say but usually all they are providing is a correct float voltage to the chassis battery. They work for any charge source (charger, solar, etc).
__________________
2002 Winnebago Brave (WPF32V)
Workhorse P32
S/N 10F71C261406
MadMaxWinny is offline   Reply With Quote
Reply

Tags
batteries, engine, generator


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to charge 2 dead engine batteries B Bickelmann Winnebago Class A Motorhomes 7 06-04-2019 10:44 AM
Generator won't start unless engine running Oldchinahand Electrical | Charging, Solar and Electronics 6 06-26-2018 06:06 PM
Winnebago 2002 Journey will not charge house or engine batteries ttrv Winnebago Class A Motorhomes 22 03-09-2017 11:42 AM
Do the batteries charge up when running the gen ewaldo Electrical | Charging, Solar and Electronics 19 10-27-2013 08:03 PM
Generator not starting unless V-10 engine is running bobpie Electrical | Charging, Solar and Electronics 11 08-12-2010 05:59 PM

» Featured Campgrounds

Reviews provided by

Disclaimer:

This website is not affiliated with or endorsed by Winnebago Industries or any of its affiliates. This is an independent, unofficial site.


All times are GMT -6. The time now is 11:37 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2022, vBulletin Solutions, Inc.
×