charging battery from generator---how long does it take?

[coolmom42]

In 2-3 years, I'm planning to convert a van to a minimalist RV, and estimate that I'll need about 100 amp-hours of power every couple of days, absolute max. (LED lighting, fan, water pump, charging electronics, maybe at some point a 12 V fridge.) So that means a 200 amp-hour battery bank at 50% or less discharge level.

I recently purchased a Honda EU1000 generator, with the intent of running home fridge/freezer in a power outage, plus the long-term intent of using it to charge a future camper battery.

My understanding is that this will require a good quality battery charger between the generator & battery bank.

Battery chargers come in different amp ratings, so how do I choose the most useful amp rating for my needs?

Is the amp rating calculated at 12 V DC output?

With the generator running at say 800 watts/12 V = 67 amps x 90% charger efficiency that gives 60 amps possibly going to a battery bank. Correct me if that's wrong, please.

So given the 60 amps possible from the generator, does the charger then become the limiting factor?

With a 20 amp charger.... does that mean it would take 5 hours to restore 100 amp-hours to the battery bank?

Just trying to figure this out. My plan is to gradually acquire smaller components and then pull the trigger on the van in 2-3 years, depending on lots of factors.

Any input appreciated!

[jrnymn7]

With that honda 1000i, you're pretty much limited to a 30a charger. Yes it may handle a 40a for short durations, but on a regular (daily) basis, and for several hours at a time, it would do a real number on the genset. Open link and click on specs:

http://powerequipment.honda.com/generators/models/eu1000i

A 30a(dc) charger will pull about 6.5 amps(ac).

With a 150Ah AGM bank, at 50%, and a 30a charger set at 14.4v, it will take about 90 minutes to do a 50-80%, and about another hour to do the next 80-90%. Take notice, that's 45Ah's in 90 minutes, followed by only 15Ah's in 60.

Keep in mind, most portable chargers are crapola. They operate outside of ones control, and often charge at inappropriately high voltages, i.e; above 15v. And converters are great for converting, but way too slow for charging in a boondocking/generator situation. You need a charger, and not necessarily a 3 stage. A mega watt s-350-12, for example, would serve you well.

http://www.12voltpowersupplies.us/

... Another YES to going solar 🙂

Good luck with your project... I converted a mini school bus.

[mena661]

Keep us in the loop on what you discover!

[coolmom42]

The plan is to start out with a good quality cooler, which I already own, possibly add a 12 V fridge at some point. The only bigger power hog that would tempt me is a microwave.

If it's too hot to be comfortable with a fan for ventilation, I'll go up, north, or home. If it's too cold to be comfortable, I'll go south, home, or to a RV park with electricity for a space heater.

But I definitely will check out the alternator capacity. On Saturday I'll be over near a large Nissan dealer that has 3 of the NVs on the lot, if time permits, I'm going to check them out.

[mena661]

You could always upgrade the alternator to something more up to the task if you need to run big power stuff from it. See MEXICOWANDERER, he's an alternator guru among other things electrical.

[coolmom42]

pianotuna wrote:
Hi coolmom,

Nice that it comes with an inverter. How many watts can they do on a continuous basis? Pure Sine Wave?

See if a 2nd alternator is an option.

I do see pulses of up to 70 amps from the alternator my dual path charging system. At about 35 amps continuous voltage starts to drop on the engine side. At that point I sometimes shut down one charging path to limit amperage and not over load the OEM 130 amp Ford alternator. I've toyed with the idea of adding a second rectifier located away from the hot engine compartment.

Duty cycle is something to not ignore. It might be an expensive lesson to burn out an alternator.

Double conversion is rarely the best path for battery charging.

You have chosen an exciting project--I wish you great times while doing so.

coolmom42 wrote:
I'm looking at the Nissan NV or Ford Transit vans, and they generally do have a heavy-duty alternator. That's on the list to double-check when serious van-looking time arrives.

They also have a built-in inverter that would allow me to plug in the battery charger at any time the van is running. The inverter plug-in while driving would be a good way to top off the batteries, since most days I will be driving some.

I'm not sure about the inverter details. That's one thing I'm going to look at pretty closely. My understanding is that it's marketed towards construction/tradespeople, so is intended to run power tools. So it should be 15 amps or so.

A friend of mine burned out the alternator on his F-350 running a circular saw off the inverter, so I'm well aware of the potential for problems. Marketing and reality don't always match for sure.

Good point about the double conversion. You people will talk me into solar yet.

Nice thing about a project like this is that a person can start very basic and then add extras as desired.

[pianotuna]

Hi coolmom,

Nice that it comes with an inverter. How many watts can they do on a continuous basis? Pure Sine Wave?

See if a 2nd alternator is an option.

I do see pulses of up to 70 amps from the alternator my dual path charging system. At about 35 amps continuous voltage starts to drop on the engine side. At that point I sometimes shut down one charging path to limit amperage and not over load the OEM 130 amp Ford alternator. I've toyed with the idea of adding a second rectifier located away from the hot engine compartment.

Duty cycle is something to not ignore. It might be an expensive lesson to burn out an alternator.

Double conversion is rarely the best path for battery charging.

You have chosen an exciting project--I wish you great times while doing so.

coolmom42 wrote:
I'm looking at the Nissan NV or Ford Transit vans, and they generally do have a heavy-duty alternator. That's on the list to double-check when serious van-looking time arrives.

They also have a built-in inverter that would allow me to plug in the battery charger at any time the van is running. The inverter plug-in while driving would be a good way to top off the batteries, since most days I will be driving some.

[coolmom42]

^^^^OK OK so I'll look at solar!!! LOL

Quite possibly in a couple of years the prices will have come down more.

[westend]

coolmom42 wrote:

MEXICOWANDERER wrote:
A question is, with one thousand watt limit what are the options in a power factor corrected charger dept? Trying to recharge 100 amp hours at 30 amps is dooming the user to listen to the generator for four hours at a stretch to charge to 75-80% with regular batteries and perhaps 80-85% with AGM. I would be -mighty- tempted to fit a 140 amp alternator to that van and let it whack the AGM's for a half hour while concurrently running the Honda. But there is a finite amount of amps that a Honda 1000 will ignite and if memory serves me correctly that figure is 50 amperes or less

I'm looking at the Nissan NV or Ford Transit vans, and they generally do have a heavy-duty alternator. That's on the list to double-check when serious van-looking time arrives.

They also have a built-in inverter that would allow me to plug in the battery charger at any time the van is running. The inverter plug-in while driving would be a good way to top off the batteries, since most days I will be driving some.

It will probably be more efficient to charge your house batteries with the vehicle's alternator while traveling rather than doing the two conversions with an inverter and charger. A separate rectifier and bigger wire will be an improvement over the stock charging system. FWIW. I have a HD alternator in my Ford truck and it is a great piece of gear. Just replaced the original battery last year. 10 yrs., one month of not-so-easy life.

I'd suggest you review solar charging some more. It is one of the best charging systems for the boondocker and is basically maintenance free. I use mine to run refrigeration and the whole system was cheaper than a new absorption fridge. I wouldn't own an RV without solar.

Battery University

[SteveAE]

coolmom42 wrote:

My background in chemistry made it pretty easy to comprehend.

It shows.
I have no doubt that shortly we will be the ones coming to you for answers to our questions.

Best wishes on your project,
Steve

[coolmom42]

SteveAE wrote:
coolmom42,

I have nothing of substance to contribute to this thread, but I do want to congratulate you on how well you have researched your upcoming project and verbalized your questions. Good job.

Steve

Thanks.

I've done a lot of research into batteries while travelling with now-former boyfriend in a travel trailer. He has good mechanical skills but wasn't really interested in the electrical stuff. My background in chemistry made it pretty easy to comprehend.

[coolmom42]

mena661 wrote:
45A charger on the Honda 1000W generators is about the max it will do.

Makes sense, thanks.

[coolmom42]

MEXICOWANDERER wrote:
A question is, with one thousand watt limit what are the options in a power factor corrected charger dept? Trying to recharge 100 amp hours at 30 amps is dooming the user to listen to the generator for four hours at a stretch to charge to 75-80% with regular batteries and perhaps 80-85% with AGM. I would be -mighty- tempted to fit a 140 amp alternator to that van and let it whack the AGM's for a half hour while concurrently running the Honda. But there is a finite amount of amps that a Honda 1000 will ignite and if memory serves me correctly that figure is 50 amperes or less

I'm looking at the Nissan NV or Ford Transit vans, and they generally do have a heavy-duty alternator. That's on the list to double-check when serious van-looking time arrives.

They also have a built-in inverter that would allow me to plug in the battery charger at any time the van is running. The inverter plug-in while driving would be a good way to top off the batteries, since most days I will be driving some.

[coolmom42]

pianotuna wrote:
Hi Coolmom,

AGM are faster to charge and can accept current faster, but recharging any lead acid chemistry to 100% will still require MANY hours of generator run time. The trade off comes with lower total capacity. A group 27 is probably not going to be 100 amp-hours.

Mostly folks settle for 50% to 90%. If that takes say 3 hours, then getting from 90% to 97% will take an additional 3 hours. Probably 97% to 100% takes yet another 3 hours.

OK after looking at the Interstate battery charts, I can see that 2X of the Optima group 31 would get me to 150 amp-hours for 75 useable. That will likely be adequate for my needs.

[coolmom42]

pianotuna wrote:
Hi Coolmom,

AGM are faster to charge and can accept current faster, but recharging any lead acid chemistry to 100% will still require MANY hours of generator run time. The trade off comes with lower total capacity. A group 27 is probably not going to be 100 amp-hours.

Mostly folks settle for 50% to 90%. If that takes say 3 hours, then getting from 90% to 97% will take an additional 3 hours. Probably 97% to 100% takes yet another 3 hours.

Probably what I'll be doing is 4-5 days dry camping at a time, at the most, followed by going home, or a couple of nights at a campground/RV park with shore power. Then I can plug the battery charger in for about 12-16 hours at a time. That should be plenty of time to get the batteries to 100%. At home, I can leave it plugged in as long as needed.

So getting the batteries to approx 90% of charge once every 5 days max time frame, then up to 100% every 5 days or so, should be adequate, from what I've read about battery life.