Thermistor Temperature Compensation For Megawatt

[MEXICOWANDERER]

It would mean running a telephone line cable between the charger and battery post.

But I am flummoxed as to the temperature range many people want. I could do this in private and not share. My needs therefore would be from freezing to 40c 104F. An inline switched ten ohm biasing resistor would help to correct deviations in voltage.

If there is no interest in this I'll save this site's server a little extra work.

The object is to create a 36-ampere battery float maintainer in which with a fully charged flooded or AGM battery a load can be imposed up to charger capacity without taking the battery out of float mode.

Different thermistors can accommodate different chemistries.

And the temperature compensation can be switched on or off, rendering the unit as an adjustable voltage charger or adjustable temp compensation floating maintainer.

[MEXICOWANDERER]

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[larry_cad]

hawkeye-08 wrote:
You need to order a couple of these and then you can go back 30 years..

http://www.oreillyauto.com/flux-capacitor.html

clicky

[hawkeye-08]

You need to order a couple of these and then you can go back 30 years..

http://www.oreillyauto.com/flux-capacitor.html

[larry_cad]

MEXICOWANDERER wrote:
Well, it's like this...

I want that 11 position, snap break-before-make switch with resistor array

Configured for AGM and flooded battery voltage span.

The Megawatt voltage divider uses a convenient 10 ohms per tenth volt calibration factor.

An ON/ON 5 ohm primary bias switch can halve the resolution doubling the count to 22 positions.

While an ON/ON/ON switch can select thermistor, 11 switch or all-out 16.13 0 ohms charge rate (for equalizing).

Yeah - yeah I can use a low resistance Bourne pot to bias thereby configure the Thermistor circuit.

**** I can only wish this stuff was around 30 years ago.

:B

[MEXICOWANDERER]

Well, it's like this...

I want that 11 position, snap break-before-make switch with resistor array

Configured for AGM and flooded battery voltage span.

The Megawatt voltage divider uses a convenient 10 ohms per tenth volt calibration factor.

An ON/ON 5 ohm primary bias switch can halve the resolution doubling the count to 22 positions.

While an ON/ON/ON switch can select thermistor, 11 switch or all-out 16.13 0 ohms charge rate (for equalizing).

Yeah - yeah I can use a low resistance Bourne pot to bias thereby configure the Thermistor circuit.

**** I can only wish this stuff was around 30 years ago.

[Chris_Bryant]

I still don't see why you don't just stick a digital pot in there with an Arduino measuring current, voltage, temperature and time.

[larry_cad]

From that explanation, I would guess that the factory pot is connected (on the high side) to a fixed DC voltage source, typically 5VDC. The low side is connected to common (ground) and the wiper arm picks off a DC voltage between 5 and 0, and injects it into the variable voltage source to adjust the output. Very typical for a DC power supply. Your plan is to replace the pot with a temperature variable resistor to control the output via temperature. I would think that a series combination of two thermisters connected from high to low, with the center point of the thermistors connected to the injection point would also work and would give you more variability. Just thinking out loud, so to speak.

[MEXICOWANDERER]

The Megawatt like most Meanwell clones, uses an accessible 1-turn potentiometer that ranges from around 11.5 to 15.5 volts.

By substituting a thermistor within the unit's voltage divider network the sensing system becomes thermally oriented.

By actually working on the units I found the inverse operation (lower the resistance the higher the voltage) has a fundamental useful voltage span that correlates to 280 ohms max down to whatever resistance / voltage level a user desires. In theory a wider scope thermistor can be used to control floating voltages from -40FC to 122F 50C.

The setup is simple - removal of the original pot, solder a length of twin wire with a quarter watt carry potential (24 gauge would be useful to around 60' total back and forth length - meaning a 30' distance between thermistor and float charger.

The beauty of this is that the thermistor could be switched in and out of circuit with a simple ON/ON switch. I am ordering a 16-position single pole click-click switch today, which would allow quite a span in voltage. One side of ON would be thermistor control, the other ON, a manual control. Of course a multi-turn pot can substitute for the click-click switch.

For that matter, another clicky switch can be used as a pull-up with inline resistors for the thermistor. Six ohm increments, and three positions could bias the thermistor. Maybe .1 volt increments negative to plus. It all could be contained in a module with voltmeter and one of Mr. Wizards inductive ammeters.

A fun project.

[larry_cad]

Do I understand correctly that you want to build a variable output, 36 amp charger, using something like an IGBT or SCR, that is controllable, and you want to use a thermister to provide the controlling input to the charger? The controlling action will be based on temperature or else a variable voltage output?