Battery Chargers

Hook the battery up first.

As Lyn said, connecting a battery would be an appropriate solution.

If you need the charger to work without the batteries, you should talk to the manufacturer. Modifying either the feedback transfer function (control electronics) or the system transfer function (power electronics) has to be done by a professional. Performing such tasks may be dangerous for the equipment or for the users, which, in the end, could get you in jail. So this better be something intended for personal use.

http://www.operatingtech.com/lib/pdf/A%20Guide%20to%20battery%20Charging.pdf

Firstly you might explain what you mean by fully and half controlled for these devices.

I am assuming that the battery is connected when you are adjusting the float and boost voltages as most chargers these days won't provide any output until they see a connected battery.

You say the voltage drops when the load is applied - how big is the load?

If the load is greater than the charger can adequately compensate for, then the obvious result is a depression in battery terminal voltage due mainly to voltage drop across the internal resistance of the battery.

How to overcome this:-

1. Reduce the load - probably not practical.

2. Increase the size of the charger so that more current can be provided to the load.

3. Increase the size of the battery bank ie. more batteries in parallel, this will increase the effective plate area and thus reduce terminal voltage depression - a short term solution as, if the charger is inadequate for the load size, then eventually the bank will still lose the ability to supply the load.

4. Change to a battery chemistry that can handle heavier instantaneous loading - LiFePo4 technology is one such type that will deliver far higher discharge currents while still maintaining suitable terminal voltage than will any of the lead acid chemistries. Again the charger will eventually have to replace consumed energy whether this be during load down time or via a larger charger.

"I am adjusting float voltage and boost voltage on no load and connecting the load"

I'm guessing that you are questioning my assumption that the battery is connected when the charger is adjusted under no load conditions.

Are you assuming that the battery is the load?

"load" may refer to the load on the battery (a motor etc.) rather than the battery being the actual load as you appear to believe - you may be correct, more information would assist in determining that.

With the above in mind, adjusting the charger output with the battery connected but with no load applied would be the normal way to do it.

OK. Your point is well taken.

Hopefully, OP will get back to us.

Anything with an impedance as low as a <...battery...> will drag down the voltage of the connected charging source until the charge level inside it starts rising. The charger may well contain current-limiting circuitry that will protect both it and the battery against over-current. In such circumstances the measured voltage at the terminals will be lower than the open-circuit voltage owing to the current being poured into the battery.

The charger will continue to pour charge into the battery until the battery open-circuit terminal voltage starts rising, during which the charging current will reduce and the charger outlet terminal voltage will rise. When the open-circuit battery terminal voltage rises to the same level as the charger outlet no-load terminal voltage are the same, the current into the battery will reduce to zero.

It is, therefore, nonsensical to try to regulate the voltage of the charger either with it open-circuit, or with a battery that is completely discharged, for that is not how a charger works.

Dear sir,

Thanks for reply.As battery charger is also a dc power supply,I want to find its voltage regulation.For that purpose,I adjusted float voltage on No load and boost voltage also on no load.Afterwards,I connected it to electrical heaters as load.Battery is not connected.Then I observed that the voltage is falling even at low dc current also.I have set the current limit at high level,but still the dc voltage is falling from the no load set points.This gives an inference that voltage regulation of the charger is not proper.hence,I wanted to improve the voltage regulation.I need forum members help to improve voltage regulation of the charger.

Repeating a fallacious assumption does nothing to solve the problem.

What the forum has, once again, is a failure to communicate.

<disconnecting>

Most emphatically, very few chargers are designed to work properly without a battery connected!! A battery behaves as a very big capacitor for smoothing the charger output & charger control circuits will be upset by the big ripple without battery.

A fully charged battery will draw negligible current & applying load to drop voltage will reduce that current [so long as voltage is above discharge level of battery]. You should allow time for voltage to stabilise after load change (battery will initially behave like capacitor, often Farads!). A voltage drop of 2% at full load would not be a problem. The important point is that the float voltage is kept right at the normal load current - voltage at zero current or when charging flat bettery is not relevant - one sets the voltage at normal load, not at no-load.

Since you have not given the battery type/number of cells, Ah capacity, specified float voltage, "end of discharge voltage"; normal load and its variation from that & timescale for variations, charger rating or where you are measuring voltage [cable volt drop charger to battery or load is usually significant] or even the voltage values you measured with what & why you think they are "not good" - help is difficult to give.

It is not clear if this battery is pure standby with mains always available or if there is regular charge/discharge [solar power?].

If the system is designed properly, the load will be OK with any voltage between boost level and "end of discharge" volts less cable volt drop, which is much more than the regulation around float voltage e.g. 2.5 volts/cell to 1.85 volts/cell [float say 2.25 v.p.c. +/- 1%] - there is no purpose in worrying about variation as "DC power supply". Note that necessary boost voltage for low temperature increases a lot from standard data sheet value.

I would suggest you investigate charger ripple level without battery connected [connect AC voltmeter via capacitor 0.1 microfarad (assuming 1 megohm input resistance of voltmeter - DVM?)] to clarify problem. Excessive ripple could affect load function.

Also advise the battery/charger parameters mentioned please.

<disconnecting>

It is very unusual for chargers to regulate without a battery connected - increased ripple without battery can upset regulation. They do not always regulate with zero charger current - maybe regulation only above 10% rated charger current.

When you write "load", we cannot know if you mean battery connected to charger without load [often the case for boost charge when load cannot tolerate "boost" voltage] or charger to battery & load in parallel.

Usually, there are current limits for float and boost (separate potentiometers) - if these currents are exceeded for some minutes after battery is connected then voltage will be reduced until battery current falls off.