Step-up DC-DC converter ( 4.2V to 12V)

you've used a bunch of terms I'm not familiar with. would you mind explaining 9Ah and cct.

over here, a battery of 12 volts with CCA of 600 is a heavy duty deal. Cold Cranking Ampere

Also, did you know that there are calcium batteries available, that yield a very high CCA rating. they need no electrolyte top ups, and something about the need to charge. It may have something to do with efficiency. I'm not to clear about it, and the guy that was trying to sell me one wasn't quite clear about it either. He reckons it never needs to be charged, but I think he's misconstrued it from never needing electrolytic top up.

Anyway, I've done experiments with HCL and calcium, and the results are quite impressive. it can increase acidity

Ah - Amp-hour - the rated capacity of the battery (you probably should have mentioned that you did not understand this when we were talking about batteries).

cct - one of the many abbreviations for the word "circuit".

CCA - Cold cranking amps. Only applicable for car batteries (which have small Ah ratings but are capable of large currents to operate the car's starter motor). Refer to Ah instead when dealing with standard batteries as it is a much better value for comparison and design.

Have a look at this battery primer for more info http://www.jaycar.co.nz/images_uploaded/battglos.pdf.

I am not sure what you are talking about regarding calcium-based car batteries, do you have a website link or a brand name perhaps (it wasn't an additive for flooded lead-acid batteries was it)?

Thanks Jack

With 50 years in electronics, this is the first time I have seen "cct" used as an abreviation for "circuit". ckt, yes... but... what ever floats your boat.

Bill

You've started with valve, I've started with transistor, btw the no"k" in circuit then why should it abbreviation be "ckt"?

have a nice day.

sufian

I've got no idea... it just... was... way back when. Maybe cct was counter-clockwise tango or something.

Bill

Sufian,

We've done this on some of our battery operated stuff, and to minimize the modifications needed, we would use a series/parallel combination to get as close to the original voltage as possible. In this case, three cells in series will get you back around your lead-acid voltage of 12V. As far as your DC-DC converter, there are many off-the-shelf solutions, or the manufacturers of switch-mode controllers usually have applications circuits in their datasheets. Linear Technology and TI come to mind. Good luck!

Tom

P.S. Your post would probably feel more at home in Communications and Electronics section.

Tom,

Thanks for the input, I've series/parallel it before.

FYI, the project is to replace lead acid with polymer lithium ion for telecommunication unit and the system cut-off at 10.6V while mine at even lower i.e 9.0V as such about 50% of usable cell capacity not utilized. And I could not modified the current circuitry which will void system warranty.

Anyway, I'll visit LT and TI website.

Sufian

National semiconductors simple switchers line has severl ICs and design ideas for step up convereters. Linear Technology has a switcher cad program on their website that will design the basic convereter for you using the LT ICs, Texas Instruments has a similar program that uses the TI ICs. Some of the ICs require very few external components and cost very little.

Thanks will visit their websites.

sufian

I am not aware of a simple off-the-shelf switch-mode power supply chip that will do exactly what you want (I know of a few that are close), but I believe you may find what you need from either http://www.linear.com/index.jsp or www.maxim-ic.com . You may find they have a battery charger controller chip that will allow you to do both the step-up and battery charging functions in one easy circuit. Other companies to try are Micrel, Linear technology, STMicroelectronics, etc.

Thank-you Jack.

Sufian

Aztec for one has perfected a number of small dc-dc converters of various types just for this use.

there are hundreds of others.

http://www.globalsources.com/manufacturers/DC-To-DC-Converter.html

Aurizon,

Thank you so much, will contact them.

rgds

Sufian

OK, here's my 2 cents for keeping it simple. Parallel connect enough LI cells to get the Ah rating you need. Make 2 more of these cell-packs. Connect the three cell-packs in series. You now have 12.6VDC (same as the 12V lead acid battery) at the Ah rating you need. Done deal? I hope the final weight is within your requirements.

Thank you, done that, unfortunately the system I'm connected to cut-off at 10.6V whereas I still have 50% cell capacity still not utilize and I could not disturb the circuitry as it will void any warranty.

sufian

According to my LI discharge curve, you should be able to extract about 80% of a 12.6V cell pack capacity and still be above 11V depending on the discharge rate, cell temperature, age of the cells, etc. Paralleling more cells (increasing the AH capacity) will keep the voltage higher at the same discharge rate. I'd prefer this type of solution to one that includes the addition of electronics. Just more things to go wrong and negatively affects the potential failure rate of the assembly. If your goal is simply to extend the operating time before recharge, this may be a viable alternative. If, however, you are looking to extend operating time and lighten the weight, well.................? My gut tells me that using a DC to DC step up converter to try and extract more from the cell pack will place an increasingly larger load on the cells during the discharge cycle causing the voltage to drop even more and wind up shutting down completely or going into oscillation (on-off-on-off-on-off) at approximately the same point without producing any significant gain to cell pack capacity utilization.

FYI, the current system is using Lead acid 12V 9Ah which last about 7 days standby time and 3 days talk time. And the system will halt when supply reaching 10.6V.

I've used 12.6V 3Ah Polymer Lithium ion, its meet the 7 days standby time, but still have about 50% unused capacity (system cut-off 10.6 but my pack is at 9.0V cut-off), where it can have another 7 days standby time available.

Cost wise the lead acid is about 30~40USD/unit for 9Ah but mine is for 3Ah, so if I were to increase it Ah then it will cost even higher. I would also need a balancing circuit for 3S2P connection not including mark-up price for my profit.

So if I were to boost it via DC converter, I may end up paying additional 10USD,...well I could live with that and still can make some money, since my pack can out perform lead acid even using 3Ah pack. I can still persuade my client to cough out a lit bit more as they are saving on maintenance cost, space and so forth, which in long run its better than lead acid. Anyhow lead pricing is keep going up nowadays so is lead acid battery then.

rgds

sufian

Get an Inverter to make4.2VDC to Carrier Frequency( You can buy from VFD vendors)

Step down using a HF Carrier Freq. transformer-a tiny device.

Rectify/smooth to get your 12VDC