Using a generator to charge batteries

My understanding with deep cycle batteries is that they will last longer and preform better charging them slowly.

Fast charging is not good for any battery.

Baz.

Spot on Bonz, but in saying that fast charging IS good for getting the beer cold if the fridge has stopped! LOL

If you have a good 3 stage charger it should not matter AS much because it will only charge them on bulk for a short period. If you were using a truck charger type thing that was just blatting them full on it would not be good. But being Gel Cell battereis you would need a 3 stage that supported that type of battery anyway. You'll find that they need to bulk charge at about 14v, then switch to about 14.7v then float at 13.8v or so. If the charger supports these batteries it will either have a switch to set it to Gell Cell type batteries or the really expensive smart ass ones may even do it automatically, but I would suggest finding one with a switch.

I'm guessing he probably doesn't want to carry another petrol motor'd contraption around with him. The Christie is a good thing for what it was designed to do, IMHO. However, it is significantly noisier than the gennie and it only has one purpose. The gennie is not only much quieter, but has the added benefit of being able to run 240v appliances.......INCLUDING a battery charger.

In short, the gennie can cover all the bases that the Christie can do; but not vice versa.

Yeah - what HE said!

Thanks very much for the idea though....

Cheers
Muddy

Even at 25 amps it would still take about 10 hrs or so to fully chage both batteries (including "charging losses"). Depending on the type of battery you may well be able to go higher than this.

Remember also that there may be some switchmode chargers (usually identified by the abscence of a large heavy transformer inside) that may not run with some of the raw AC generated by some generators ("dirty AC").

The way to fix that problem is to also run a 75 or 100 W incandescent light whilst running the charger. This puts a load onto the generator that settles it down.

PeterD

Yeeeesss....

The output from the DC connection would not seem to be a lot of good for the batteries based on that reading! And 8 Amps charging current is going to be a slow way of doing the job!

Looks like I am going to be looking at a 25 Amp 240v Smart Charger which will give the batteries a good drink while also leaving capacity to run the fridges (70 litre Trailblazer and sometimes a 40 Weaco) and computer direct off 240 while the genny is running and give the batteries a good rest.

As Bonz pointed out above a 50 Amp charger is pretty huge and probably pretty big dollars as well as physical size. Suffice to say that genny capacity is not a problem for running a battery charger and that is what I wanted to know.

Wonder if people out there realise how little of their genny capacity they are using if they only use a 1 or 2 KVa genny for charging batteries....

Cheers
Muddy

"The output from the DC connection would not seem to be a lot of good for the batteries based on that reading! And 8 Amps charging current is going to be a slow way of doing the job!

Looks like I am going to be looking at a 25 Amp 240v Smart Charger which will give the batteries a good drink while also leaving capacity to run the fridges (70 litre Trailblazer and sometimes a 40 Weaco) and computer direct off 240 while the genny is running and give the batteries a good rest."

You've summed it up perfectly,

Geoff

Did you actually have a load connected when you took that screen cap??? Have you ever wondered why they recommend that you do not disconnect the battery of your car when the engine is running????? This is EXACTLY why.

The charging output (of the gennie, and the cars alternator) needs a battery connected to to regulate the output.

Deep and meaningful discussions could ensue from here on, but sufficient to say being armed with half the information is not necessarily helpful...

Hook a battery up to the charger output on the gennie and then show us the waveforms as well as the measured voltage and measured current.

When you apply a significant load to the DC output on a portable generator it will drop down to 13 V or less. This makes it not very good for battery charging purposes. It is useful however to put enough charge back into a battery to start an engine.

PeterD

No sheite Sherlocks?

Geoff

Or,

"leaving capacity to run the fridges (70 litre Trailblazer and sometimes a 40 Weaco) and computer direct off 240 while the genny is running and give the batteries a good rest"

Would form a handy base load along with the charger,

Geoff

Hi Geoff

Yes, quite right.

I also use the time to charge the laptop and boil the jug on my EU2.0

An internally regulated alternator can give up to (your) "60 to 110 amps" at the terminal on the alternator, it cannot "push' current out if there is nothing to absorb it

The "regulator does nothing to regulate any current output, it regulates the output VOLTAGE of the alternator only. The amount of current charge the alternator puts out is a respose to the difference between the battery voltage and the voltage that the alternator has been set to. As the battery voltage rises (from being charged) "to meet" the alternator set voltage, the current reduces (ohms law, NOTHING to do with the regualtor).

Gary,
I can only assume the two batteries are connected to the alternator/regulator, lol

Also remember a vehicle alternator puts out 13.5 - 14 V when the motor warms up due to the temperature compensation built into the alternator. This is less than the output of a three stage charger in the absorption stage - so a battery will not receive full charge if you use a vehicle alternator to charge it.

PeterD

Peter,
Simplistically stated, while the alternator/regulator is putting out more power than what is in the battery, the battery will be relieving a charge.

Eg, if the Alternator/regulator is putting out 13.5v and the battery is only 12.2v the battery will become fully charged at 12.66v (wet cell Cranking battery) because the power going into the battery is greater than the power contained with-in the battery, said with-out using any 'big words' lol.
The battery will show as 13.5v when tested, while being actually charged, however this is known as surface charge and will disapate when the charging stops.

Some explain it using the 2 x buckets of water syndrome, if bucket (a) is 50% full and bucket (b) is 100% full, and a tube is run from the base of (a) to the base of (b) the water will level out in both buckets at 75% full, however if you continue to add water to bucket (a) it will continue to add water via the tube to bucket (b) till (a) is also full.

Mainey

We can not use simplistically stated statements when calculating charge currents into batteries. The old bucket of water is only good for explaining purely resistive circuits. When you start talking about capacitive, inductive or chemical loads things get complicated and other things have to be taken into account.

There is a magic figure of 2.2 V/cell which is the voltage above which has to be exceeded to put any charge into a well charged battery. Sure a discharged battery will take some current from a lesser voltage but not much current. I once had a small, fairly well discharged car battery that I used a regulated power supply to charge - I had to wind up the voltage to its maximum (16.5 V) to get 1.5 A into the battery - it took nearly an hour before the current came close to the PSUs maximum of 10A and I had to commence reducing the voltage to prevent the overload circuit cutting the output off. This should demonstrate to you that it is not a simple bucket of water or Ohms Law situation when you start to calculate battery dynamics so you can forget your buckets of water.

Manufacturers of three stage battery chargers do not set their absorption voltage at 14.4 to 14.7 V for no valid reason when they recommend their chargers for charging batteries with a 20 hour capacity of up to 25 times their maximum output current. This voltage incidentally is a lot higher than a car's alternator runs at when the engine bay is at running temperature.

PeterD

Actually, you are both off the mark.

Automotive type batteries, whether they be wet cell, Gel Cell or AGM, will not fully charge unless the charging voltage is 13.8 or higher ( this will vary slightly between makes ) and as most alternators have a constant output voltage of between 14 to 14.3 volts, there is no reason why your alternator can not charge all your automotive batteries to at least 95%, given enough time.

With exception of the Discovery 3 and Range Rover Sports, if your alternator is running at less than 14 volts once the motor is at it’s normal operating temperature, it’s time to have your regulator checked.

All batteries require at least 13.8 volts at 25c to get the chemical reaction working properly to allow the battery to take a full charge.

Anything above this 13.8 mark will simply speed up the charging rate. In other words, the high the voltage over 13.8 volts, the quicker your batteries will charge.

Note, there is an upper limit to how high a voltage a given battery can take without damaging it. This upper limit varies greatly between makes and types of batteries.

Always go to the web site of the manufacturer of what ever brand battery you are using and get the correct charging info for your specific battery.

Cheers

drivesafe

Auto alternators have temperature compensation. For an example of their curves see www.landiss.com/battery.htm - The voltages you are quoting are for engines that have their bonnets up and their engine compartments are not up to running temperature or they have been sitting for a while and have cooled down before restarting and the alternator voltage tested. Both my disco TDi and Td5 output 14.4 V when first started and drop to 13.7 V about 5-10 km down the road. This is sufficient for the starting battery to recover.

The general consensus among electrical engineers is that 13.8 volts is only a maintenance type charge, it takes a higher voltage to achieve a top up type charge.

For a fuller understanding on the subject of deep cycle house type batteries have a look at
http://www.victronenergy.com/upload/documents/Book-EN-EnergyUnlimited.pdf
Take particular note of sections 5.2.2 and 5.2.3.1 Automotive electricians have a simplified view of battery charging as they are only schooled to any depth in starting type batteries. To get a good understanding of deep cycle batteries you need to consult a marine electrician who has had extensive experience with boats that people live aboard.

PeterD

Nothing beats hands on experience, so my recommendation is that anybody wishing to find out just how there alternator is charging, is to measure the voltage at the battery after you have had a bit of a drive.

My D1 was always 41.1 volts no matter what the temperature was.

Never bothered measuring my D2 ( didn’t have it long enough ).

My Mk III RR is rock solid 14.3 at all times, hot cold or otherwise.

My D3 varies and as stated, like the RRS, is the exception to the norm.

Some late model D2s do have a varying voltage but this is because they were the first stages of the new system found in D3s and RRSs.

Of the many vehicles I have installed dual battery systems in, few had a continuous voltage level of less that 14 volts.

Don’t care what one reads in a text book or similar, I design and manufacture dual battery controller and base their development on out-in-the-field findings.

There are a very small number of vehicles that did have temperature modifying voltage regulators but for the vast majority of 4x4s, 14 to 14.3 IS the average.

Only the D3 and RRS are designed to charge as low as 13.5 and as high as 15.7 as controlled and required by the vehicle voltage monitoring systems.

Cheers

So reading the various posts above;

You do have to have more power going INTO the battery than what is contained with-in the battery to charge it ?

The problem is the EXACT numbers are now in dispute :((
but as can also be read even these numbers will vary from vehicle to vehicle !!

A bucket of water won't recharge a battery lol

Hi Mainey, as far as current goes, there is not much difference between types of batteries.

The vast majority of automotive batteries require somewhere between 5% and 10% more current during charging than will be stored. So for every 20 amps needed by the battery, you will need to supply between 21 and 22 amps of charge.

In small dual battery set ups, the additional current is not all that important but once you start getting up in storage size then the additional current requirements should be factored in.

Cheers

Charging current overheads vary as a proportion of rate of charge coupled with size of battery.

If you have a 100 ah battery it may take 53 hrs at a 2 amp charge rate (106 ah going in), but it will take 5.5hrs at 20 amp (110 ah going in) These are basic figures off the top of my head, but are pretty representitive.

If you had a 10 ah battery you could reduce the currents of the above example appropriately (ie one tenth), but not the times. (normal batteries)

Some AGMs are designed to take an effective "not limited" charge rate and can be fully charged up to their capacity within two hours (some small 10-15 ah ones in less than 1 hour using a 20 amp charger), it is at these points that you see the "charging rate x time" equations take a bit of a hammering and things get less efficient, but only up to about 20% over .

Notwithstanding, there are other influences that affect a batteries ability to absorb current, such as battery construction and heat, as well as age, etc. There is no "one size fits all" answer only the best solution to a particular set of variables.

Hi GarylnOz, if only it was that simple.

AGM batteries in the right situation, can be charged much quicker than conventional wet cell batteries.

Wet cell batteries, for a start, should not take so low that they need to have that amount of amps replaced.

Next, even taking one to as low as 25% State of Charge, will require at least 6 hour to 8 hours to fully recharge these types of batteries.

Just because you have a supply current of 20 amps at a given voltage does not mean the battery will take 20 amps constantly till it’s fully charged.

You will get the bulk of the charge, up to about 75% then the current requirements of the battery will taper off pretty quickly from this point and will continue to drop off as the battery gets closer to full charge.

Cheers.

As I stated in an earlier Follow-up the 12 V output is not capable of charging a battery to any great depth so it is not capable of destroying your battery.

PeterD

Sounds like a good choice Muddy. I run a 1KVA gennie and a 25Amp CTek multi stage charger. I now carry four AGM deep cycle batteries (2 in Hilux, one in CT and one for elec motor in boat). When charging with the gennie, I generally only charge till absorbtion stage is complete. At this point battery is probably at least 85% to 90% charged (but this is a guess) and current draw drops to just a few amps. Not worth running the gennie to suck out that final bit of charge. Whenever I have access to 240V mains, I fully charge.

All works great for me.