Battery Charger Question

I am no expert on these matters however I have had a ctek 25000 for 18 months and it has been a wonderful bit of gear.
I have often had accessories running whilst charging and probably due to ignorance have never noticed any difference in charge times.
Cheers

Doddgey

Hi

I'll forward your question thru to Don, our electrical design engineer, and get back to you with an awnser asap.

Give us a call if you would like to check our prices on CTEK, Xantrex and Victron.

cheers

martin

The charger regulates the voltage not the amps.

So if you connect something that pulls 15 amps, then the output of the charger will increase.

It is not the charger that runs your accessories while charging.
Any load will draw its power from the battery bank and the charger is used to recharge the battery while it is supplying power.
So, providing the battery is of sufficient capacity to run your accessories while it is being charged by the battery charger, you should be OK.

The term "smart charger" is used to classify a charger that has multiple charging cycles and can detect what one to use at a given time.

If your total number of accessories exceed the ability of the battery to provide a reasonable amp hour rate, you need to do one of three things.

1. Reduce the number of accessories you use at one time.
2. Create a larger battery bank by connecting additional batteries in parallel.
3. Use a generator of sufficient size to run all your stuff.

There is an option on the Ctek to use it as a power source but this is for relatively light loads.

I am curious what you run that draws a heavy load such as you mention.


Bill.

Hi Guys, thanks for all the replies.

Martin, that would be great, I'd be interested to hear what he has to say.

Phil G, this sounds like the way I would expect it to work but do you have any literature that shows this? There's certainly nothing solid I could find on any of the manufacturers web sites.

Bill, I've heard this statement before that it is the battery that runs the accessories, not the charger. I'm not sure exactly what context this is meant to be in. Surely while the charger is connected and running and your loads are less or equal to what the charger is supplying then it is the charger running the loads. Certainly no power is coming out of the battery in that circumstance so the power has to be coming from the charger.

I'm not running all that much but these things add up pretty quick. The fridge is 77W when it is running, the lights are 2 amps each x 3, stereo could be up to 10 amps I guess + other accessories such as battery chargers and phone chargers. When on battery I only run the fridge and 1 light and the fridge doesn't come on all that often. However, when the generator is running I would prefer to turn on all the lights and run the stereo and charge anything that needs charging. If my battery charges at a rate of 10 amps I would have thought I could run 15 amps of load and still have the charger charge the battery (assuming 25 amp charger).

Currently I'm just using a computer power supply that I modified to bump up the voltage and that manages to run everything and charge the battery but it's not very smart and probably won't be very good for the battery. However, I don't really want to spend $400 to get something that doesn't cut the mustard.

What I don't understand is why these chargers don't have a shunt to measure the load and simply ramp up their output to compensate.

I got this reply from ctek today:

Hi

Thanks for your question.

The chargerwill continue to charge the battery with the same output amps that the battery recive.

Best regards

Pierre Lofgren

I'm not really sure what that means but I guess it means that the charger won't supply any extra current when you turn on devices. I've had a similar cryptic reply from projecta from someone who used the term "amps per hour" (so basically he doesn't really understand the basics). Considering also the reply from the other thread that stated using load while charging will damage the batteries I'm thinking that these chargers are fundamentally flawed in that none of them measure the load separately. I thought the whole idea of them was to charge batteries AND run the load at the same time. If you're away for several weeks at a time and only run the generator for a certain amount of time per day then how are you meant to charge without running the accessories? I would imagine that most people would be like me in that they run the generator only at night, right when you want all the lights on and the stereo.

Thanks peter, I guess that answers my question. I was hoping I was wrong. One of the very first questions that popped into my head when I started looking at these chargers was how do they distinguish the load from devices vs load from charging the battery. It's amazing that in 10+ years the industry hasn't come up with a better solution, especially considering how simply that solution would be. One thing I find interesting is that these charger can operate as a power source but only at 5A for what is meant to be a 25A charger. Surely if it's a 25A charger then it can put out 25 amp.

I'm really not sure which way to go now. I was thinking that I could go with a lower amperage charger and use the computer power supply to run devices when I was on power but the problem with this is that I don't get the real kick that a battery can provide when there is a sudden load (eg fridge turning on)

With regards to your mention of the alternator and ECU that was one option I was looking at, creating a 12A geny with an alternator and motor. I mean why run an inverter generator that turns 12V into 240V just to use a charger to turn it back to 12V and then an inverter to turn it back into 240V again :-) I just need to work out how to hook up an ECU into the equation and make it think it's still in the car. That's a project for the future :-)

Where the current comes from is not all that relevant.

Lets suppose we have a ctek XS25000 and a 100AH battery and a fridge connected with a run current of 6 Amps.

Using the specs from the manual here. page 6-7.

1. Desulphation - not relevant here.

2. Soft start. Charger puts out 25A until the battery reaches 12.6 volts. If the fridge runs in this period, 6 amps goes to the fridge and remainder to the battery. As long as the battery reaches 12.6 in less than 4 hours - no problem.

3. Bulk. Charger puts out 25A until battery reaches absorption voltage 14.4V.
Max 20 hours. Any extra load will increase the charge time eg 6 Amps to fridge when running, 19A to battery etc. The only effect of a load will be to slow the charge time. As long as the battery makes 14.4 V in 20 hours, no problem.

4. Absorption. The charger maintains a voltage of 14.4 volts by adjusting the current until the current drops to 4.5A. Max 12 hour. An extra load in this phase will cause the charger to adjust it's current to maintain 14.4V. In this phase there is the possibility that an external load could cause the charger to maintain this mode longer than intended as any external load will be in addition to the 4.5 Amps going to the battery that the charger is monitoring. An intermittent load like a fridge is not a problem as when it stops running the extra load disappears aned the charger senses the reduced current and changes modes. A constant load like lights could cause a problem as the charger cannot sense the 4.5A end point accurately. EG 2 Amps of lighting load would confuse the charger as it would continue until the current drops to 4.5A, 2.5a to the battery, 2A to the lights. The 12 hour maximum time will protect the battery.

5. Analysis. Checks the battery voltage after 3 minutes. If battery drops below 12V indicate error. An external load here could cause an error if it causes the battery voltage to drop to 12V.

6. Float. 13.6 volt for Max 10 days. The charger is controlling the current to hold the battery at 13.6V. Any external load will cause the current to adjust to maintain the 13.6V

As long as the external load is within the capabilities of the charger output, the only thing to consider is the extension of the absorption phase time.