Thanks Dougy: some useful information in that (long) thread.Yes.
For a previous dummy load project, schematic and results, see https://www.electro-tech-online.com...emp-control-fan-load-bank-pwm-circuit.128753/
spec
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Thanks Dougy: some useful information in that (long) thread.Yes.
For a previous dummy load project, schematic and results, see https://www.electro-tech-online.com...emp-control-fan-load-bank-pwm-circuit.128753/
Linear is simple. I just don't like to dump 1000s of watts into silicon. Probably because I spend hours every day trying to not put heat into silicon.
30 years ago I made truck/bus alternator testers. (12/24 volt) Used car head lights as a load. Could not stand the heat. Pointed the light up and heated the sealing. Kept me cool. At that time head lights were cheaper than resistors.
Then you could get really fancy and measure the actual battery voltage and then do all sorts of calculations in the Arduino
What's the consensus?
Hey Spec,
I've got a friend who has some 1 ohm resistive load coils that come out of a commercial load tester. I've yet to have one in my hands so I can't verify any specs on the units apart from apparently they are 1 ohm. He tells me they resemble a stove top element in appearance. When I get my hands on one I'll upload a pic to show you. May or maynot be useful?
Sorry EF,Hey Spec, Haha that's fine! Though your missus could have been a touch more considerate and asked me if that was okay to go shopping . Joking aside, have you had a chance to figure out more of the layout/components? I don't want to imply any pressure for a time crunch, I'm more like a young boy in a candy store type excitement
I agree with your logic here, Also seems due to the cost of the low inductance resistors for PWM style the cost will significantly be reduced by going with the linear approach?a linear approach has non of these problems and represents a lower risk and shorter development time, in my opinion that is.
Should be just right for toasting marshmallow while waiting for the test wouldn't you say.The expelled air will be around 80 Deg C
I've had plenty of experience bashing my head against metal, should be well qualified for the jobon the assumption that you do the metal bashing
Good points Ron.What happens when the battery is removed?
C4 holds voltage for a while.
FET current goes to zero.
Error amps go to full on. Gate voltage = 24-1.5=22.5V. Max gate voltage should be 20V.
What happens when the battery voltage is low?
Error amps go to full on. Gate voltage = 24-1.5=22.5V. Max gate voltage should be 20V.
If the supply was 15 to 21.5V this problem does not happen.
RS
A low voltage cut-off circuit would be pretty straight forward to implement, except that lead acid battery voltage is not very well defined, compared to LiIon, for example. I am assuming lead acid batteries.Will this operate unattended? If so, then I would suggest adding a low voltage cutoff circuit to stop the discharge when the battery falls below x volts. Otherwise, the current will be constant down to a point, then will taper off, but the battery will keep being discharged well below its damage point. And be aware that, as soon as you remove the load current, the battery voltage will rise again. So either give the low voltage trip a fair amount of hysteresis, or make it a latch off function.
Yes, as said previously, the wiring, connectors, etc need to be substantial and high temperature. The layout is also important, although not as important as with a PWM approach for two reasons: no frequency considerations and each channel has lower maximum currents.the effective system resistance, including interconnections, needs to be chosen to ensure that the constant current range continues down to whatever minimum voltage you need to discharge the battery to.
Actually the cutoff voltage is well defined. It's just not a single voltage for all discharge conditions.Also good points ChrisP58; be interesting to see EF's views on them.
A low voltage cut-off circuit would be pretty straight forward to implement, except that lead acid battery voltage is not very well defined, compared to LiIon, for example. I am assuming lead acid batteries.
spec
Actually the cutoff voltage is well defined. It's just not a single voltage for all discharge conditions.
All batteries from reputable suppliers will have charts and graphs on their data sheets for a given battery, showing the minimum recommended cutoff voltage for different discharge currents.
No worries there. The TS has said "Fortunately I'm not working on a budget, whatever it costs will be my budget." ! That must be a first for ETO .you can just keep adding channels but this makes the unit bigger, more complex, and more expensive.