wanted 10 amp battery charger schematic ?

How much are you prepared to pay? Do you want off-the-shelf or DIY?

"Ross Herbert" "mark krawczuk"

** An off-the-shelf or DIY ***schematic*** ???

............ Phil

Touche Phil...

Ok, the first question still applies though. It all depends what parts the OP has on hand. If he has a suitable transformer and bridge rectifier he might add a Projecta 2 stage charge controller like the BM140

and discussed in this forum If it does indeed cost only $50 then building something from scratch might be more expensive.

Ross H

DC supply--->current limit cct----->voltage regulator cct--->battery

When first connected the battery charges at 10 amps max set by the current limit circuit.

As the battery volts rise to near 13 point (whatever you want) volts, the current drops off to a trickle or float charge.

If the float charging is happening too soon just fit a switch or knob to bump up the voltage regulator output so that the charger operates in constant current mode for however long you want. 10 amps times 10 hours = 100 amp hours.

Here is an example of current limit regulators and constant voltage regulators using LM317

Look at the bottom left hand corner of page 16.

Build those two circuits and see if they please you knowing that the current limit is 1 amp. If you are happy, boost the current handling of both the current limit and voltage regulator circuits to ten amps. That data sheet has some ideas. The web will show you more current boosting ideas.

If you had a handful of tiny toggle switches you could put ten in a row that switched in or out ten LM317s set for 1 amp current limit a piece connected in parallel. That is a bit over the top I know but I like that idea. Simple, and easy to see what the current is set to. Five switches on gives five amps. Ten switches on gives 10 amps. Forget that idea if you have to buy retail.

Regards, John Crighton Hornsby

Basic requirements are a transformer and a rectum frier. You'll need a hefty transformer (150VA at least) and a 50A bridge rectifier. You'll probably find a schematic in the back of the DSE catalogue (if they still print one).

You should also note that most commercial chargers only have around half the claimed output -- ie a charger labelled 10A will output around 5A. They apparently use some tricky electrical formula, like multiplying the actual DC output by 2. The price tends to rise exponentially if you want real amps (as does its capacity to boil batteries dry).

It's no longer basic if you want it regulated. Easiest and cheapest way for only 12V use might be to to use Oatley's solar regulator kit in conjunction with a rectified supply or basic charger. It's a very nifty regulator circuit (costs around $30).

If it is only for a 12 volt battery you can probably buy a hefty regulated DC supply for a lot less then a commercial charger. Wes have a 13.8V 6A supply for around $100 (trade). Some adjustments will be required -- not exactly rocket science but some basic knowledge necessary.

Jaycar once offered a kit for a 6, 12 and 24V 10A regulated charger from Silicon Chip, which they've since dropped. Price at the time was around $200 for 6 and 12 volt or nearer $300 for 24V 10A (transformer upgrade required). Alternatively you could use a smaller transformer and limit the output to 8A. You can no doubt buy the reprint from SC and source the necessary bits. It's a relatively complex project for a beginner though. It also has a raw output of 50V or so which isn't without risks for the unwary.

I've been using one for a number of years without serious complaint. Price wise it was a bargain.

-- John H

"John_H"

** Nearly all car battery chargers are labelled with " RMS Amps " - which is a blatant scam. Because current is delivered into the battery via 100 Hz pulses the RMS value is much higher than the average DC value. Of course, its the latter that actually produces increased charge in the battery.

The practice arose from the common use of moving iron current meters to monitor charge rate - these meters are rms responding by nature.

............. Phil

If you do have a suitable transformer and bridge rectifier you might consider the add-on picaxe circuit in Silicon Chip Circuit Notes Sept

2004

There is an updated (Jan 05) program listing in a zip file at the bottom of the page.