Running a <span class="highlight">battery</span> charger with load connected to <span class="highlight">Battery</span>

Hi Peter,
Thanks for the great explanation.

I must say I had not counted on running the genny for that long! It sort of defeats the purpose of having the inverter if thats the case.

The guy I bought the property off just used have the genny & because its so quiet out in the Mallee & the noise of the genny was so intrusive I decided to set up the battery & inverter system figuring mostly I could use the battery for power. Actually I have not set it up on site yet. I have it set up at home giving it a dry run before I commission it at my property in 2 weeks time.

I must say that the solar panel idea sounds like the go, particularly since there is no shortage of sunshine out in the Mallee where the van is located.

Based on the fact that that I will only be drawing a small amount of power from the inverter (a few compact flouros in the van & laptop at night) in addition to the Engel fridge, do you reckon a 10amp RMS charger is the go or would a higher output be ok for the battery? Less genny run time the better I reckon because I hate generators when I am camping!

Thanks again
Stuart

Hi Peter

I have a 40AMP smart charger that has all the stages and modes you speak of. I have bought it to use with our camper trailer that is fitted with 2 x 100amp AGM Batteries. (Camper to be delivered soon)

I have used it recently with a loaned trailer fitted with 1 x 100amp AGM and it seemed to work really well.

It automatically detected the amp level required to charge the battery and also showed the level of charge of the battery etc on the display.

My question is that I noticed the power supply setting on the charger but have no knowledge of what it does. So I subsequently left the charger in the auto mode. I was running 2 x Waeco fridges at the time. It all seemed to work fine both plugged into 240 power at a caravan park and running through our Honda EUi20 Generator which we ran for 3 - 5 hours each evening.

I was just wondering if you could expand on the power supply mode setting so that I can get a handle on what it does and how I should get the most out of the charger.

For instance if we are in a caravan park and plugged into power all the time should I leave the charger in power supply mode all the time when running the fridges.

Appreciate you input

Regards

You're most welcome Stuart.

Your daily load budget looks to be in the vicinity of 60Ah (fridge: 2Ax24hr, lappy 4Ax2hr, lights: 1Ax4hr).
Due to battery inefficiencies, you're looking at putting 70Ah back into it every day.
85% of that can be done by quick boost/ and a bit of absorption charging at 14.4~14.8V, and the remainder comes from the solar panel.
Using the 10A charger, the genny will have to be run for 70*0.85/10 equals almost 6 hours.
A 25A charger (which delivers the max recommended charging current for a 100Ah AGM battery) takes 2.4 hours for the same task.

If 2.4 hours is still unacceptable, then there is an option which requires you to run the genny for only 50 minutes.

Batteries need to be of the spiral wound AGM type for this.
Select two of these 50Ah units wired in parallel.

The charger needs to be able to deliver 70*0.85/0.83 equals 72A, to achieve this feast.
Another option is to use two 25A chargers in parallel, in which case the run time is 70*85/50 equals 1.2 hours.

So these are your options.
For more information on the chargers and batteries, pls check my profile.

@ Jason,

yes, when on a permanently powered site, definitely select 'power supply' mode.
In this mode, your batteries are being float charged (they only take in very little current during this), and the rest of the 40A on tap is for the loads.
'Power supply' mode is the same thing as a single stage charger permanently set to 'float' level.
Still, battery temperature compensation is important for best battery life, so attach the sensor to them.

Note that when left in 'auto', there is the real possibility that the boost voltage is kept up for extended periods of time.
This leads to over-charging and gradual loss of electrolyte.
I estimate this loss to be in the vicinity of 1~3 grams per hour.
In a typical 100Ah AGM battery, you can afford to lose around 0.3~0.4 litres of water over its life.
So there you have it: if the battery is left to dry out at the above rate for 10 hours every day, then the battery will be toast in a few weeks time.
That's why the bulk/absorption stage needs to be controlled very tightly by the charger.

Any interference from concurrent loads during charging potentially shortens battery life.

cheers, Peter

Wow this all gets pretty complicated!

Actually I do understand Peter's explanation & I would certainly be fine with switching modes of the charger I purchase but what bothers me is that when my kids go up to my place on their own there is no way they will switch anything over. In fact I reckon they will wonder why all the food in the fridge goes off because they have flattened the battery by not charging it for 3 days.

I would like to automate the charging side of it if I could so that basically someone can crank up the gennie from time to time & than forget about it for a while. I guess to a degree the solar panel does that.

Hi Peter,

Thanks for the explanation again. Your a wealth of knowledge. I was typing the above response while you were responding to Jason's & my second request.

I don't think I will go down the AGM battery path at this stage as I will be setting up a more permanant power system to run my bore pump when I get the property paid off & I build a cabin there. So for now I will get a high AMP charger so that I can run the genny for less time. A few hrs run time in the afternoon before sunset while we go off for a birdwatch at the dam, will be fine & I will get some real long extension leads so the gennie can have it's home behind a nearby sandhill.

Regards
Stuart

Stuart,

yes, you get away by operating the batteries in a partial state of charge for a while (means float charging them which stops dry out, but adds sulfation)

Instead of 8 years, you probably get 2~4 years out of them by doing it this way.

So you just have to budget $65.00 per year for the battery instead of $25.00 :)

AGM batteries can be had for peanuts nowadays, which makes this a feasible option.

cheers, Peter

G'day Stuart.
Have read the replys to your question with interest, I also have battery charging dilemnas from time to time.

Of course the most important thing is not to leave any battery completely discharged for any length of time and I would see this as part of your problem.

I agree, solar is your most appropriate solution, but there will be times Like quite recently) when the sun just don't shine and the generator is imperative.

Depending on the type of gen. you have there can be way to make it almost silent.
Our gen. on the farm (240v.) was a single cyl. 1500rpm Lister which was very noisy.
I put some sisalation on the shed wall with batts behind, dug a hole in the ground and buried a 44gal. oil drum, connected the exhaust to the drum by welding a pipe socket to it and a vertical outlet through the shed roof.
It was very effective.
mike

Hi Mike,
Thanks for the info on leaving a battery in a discharged state. I already am aware of this because my friend who also has a property with a small cabin is forever leaving his batteries flat for weeks on end & then he wonders why they dont last long!

As for the noise of the genny I have actually made a sound deadening enclosure for it & will be trying it out in a couple of weeks. i have made sure it is well ventilated too.

Stu

Thanks for the great info Peter.

I have been told that the charger I have is suitable to leave connected to the Batteries (2 x 100amp AGM's) all the time (as it will go into float mode) when the camper is in the garage. Is this recommended or is it better to put the batteries on the charger only every couple of weeks or similar. No load would be connected up to the batteries at this time.

Also when charging the batteries from the charger of an evening using the Generator, is it better to disconnect the fridges during this time?


Thanks again.

Hi Wayne,
I am reluctant to spend too much on my system at this point because I will be setting up a much bigger energy system on site in a couple of years so would rather keep the cost down due to this temporary system becoming obsolete then.

Stu