Quick question about battery chargers and temperature monitoring

[tron9000]

I'm just jotting down some thoughts on a Lead-acid battery charger I'm cobbling together with some parts kicking around my spares bins and don't want to purchase that many components, charger on a budget if you will. 

Basically a lm317 or 350 and an op-amp to monitor battery voltage and switch charge voltage when battery is charged.

anyway, I thought about an over temperature cutout switch using an LM35, an op-amp(1 of 4 on a LM324 - cos i got a few knocking around) & a relay, but where do you place the lm35? on the battery or on the heat-sink of the voltage reg controlling your charge voltage?

my design would be a lot neater if it was adhered to the heat-sink of the vreg, but that's not good if i should be monitoring battery temp and i get acid everywhere when the thing goes pop!

anybody offer some thoughts?

cheers

[Joules]

Download some of the well known battery charger manuals and see how they charge batteries.  The expensive chargers do have a temperature sensor, but that is only used to monitor the ambient temperature the batteries are sat at so they can adjust the charge and float voltages for the battery depending on the season.  Our CTEK charger is an 8 step charger, you can pretty much hook up a battery and forget it over the winter.

If your battery rises significantly in temperature, your probably boiling the acid and if its a gell cell you have most likely split it     Not all lead acid batteries use the same chemistry.

[Harvs]

You would need to be putting a lot of power into most LA batteries to see a significant rise in temperature, as they're a huge thermal mass.  The only reason I've seen battery temp monitoring of LAs was to correct the float charge voltage.

[Harvs]

Download some of the well known battery charger manuals and see how they charge batteries.

Or even better, grab the datasheet for the series of batteries you plan on charging.  Admittedly I'm looking at quality Odyssey batteries, but they have a significant amount of information of charge profiles and life expectancy in them.

[w2aew]

Different battery technologies & chemistries have different requirements for proper charging and charge termination.  Most of the lead acid battery chargers I've see simply monitor charge voltage and transition into a float charge mode when full charge is reached.  Other rechargable technologies such as NiCd and NiMH usually use a combination of time, negative delta-V (a drop in voltage at full charge), and temperature (which increases dramatically at full charge due to increasing internal pressure).  Bottom line - there is no universal charging method or charge termination method - and not all of them require temperature measurement.

[tron9000]

thanks for the input guys, I have a bit more to go no now.

and just a little something I found on batteries whilst doing a bit of research: http://batteryuniversity.com/ may be of use to some people.