Help with Water Pump

[alec_t]

I'm suprised the FETs don't get hot when the pump stalls. Alec, Do you think they are ok?

Average FET dissipation when the pump rotor is locked is ~2W according to the sim. Should be ok.

With the battery out the voltage from the regulator will be set at 13.6 volts. So it there is 20 volts there should be 12 volts (13.6) as well.

Good point. Wasn't wearing my thinking cap .

 

[ronv]

Average FET dissipation when the pump rotor is locked is ~2W according to the sim. Should be ok.

That would be right if the fet was full on, but the current limit makes it so there is about 10 volts across the motor and another 10 volts across the FET. That puts it up at about 40 watts. But having said that it is only on for 2 seconds and off for about 20 so the average is only 4 watts. My guesstimate on the heatsink based on the diminsions is about 7C/watt so the heatsink will go to about 53C, but the junction will be at about 85C during those 2 seconds. Toasty, but should be ok don't you think?

 

[alec_t]

it is only on for 2 seconds and off for about 20 so the average is only 4 watts

Thanks for the temperature calculations, Ron. I was getting 'on' for ~1 sec and 'off' for 20 in the sim, hence 2W average. Guess we were doing something different . Either way, with the alarm sounding I don't think Joe will leave a pump stalled for long! So the heatsinking should be ok.

 

[KeepItSimpleStupid]

Junction design temps are usually much higher than 85 C. More like 120 C, if I remember.

 

[alec_t]

@ronv

I don't think D1 is required if the input to the 317 is moved back to the other side of the PDM diode

With that connection but without D1 there will be a 0.4V (one Schottky diode drop) reverse voltage across the 317 when the 20V drops. Is that enough to turn on something inside the 317 and harm it ?

Edit: Shouldn't cause harm, since a diode across the 317 is the standard way of protecting it.

 

[KeepItSimpleStupid]

@everybody

Does it make any sense to do the following:
1) when on battery backup limit the amount of time the alarm sounds: e.g. 10-20 minutes.
2) When power is restored, alarms are continuous with the silence switch, I think, as designed.

Discuss the ability to include a "I was running on backup power" indicator. I'm just throwing out by being a devil's advocate. i don't think it's needed.

The suggested 3 power supply system, I think, makes sense.
How, exactly would you want to power the alarm module?

 

[salty joe]

Re post #1726The effect of power failure was something I didn't take account of for the 7812(s) used in the Tide and Wave Controllers . Apologies, Joe. Those should be revised by connecting a reverse-biased diode between the input and output terminals of the/each 7812. If you have a spare 3A Schottky that will do nicely (although a bit OTT).
That's an option (which would avoid having to add diodes across the 7812s). Or Joe may prefer to keep the control of the other pumps entirely separate.

I have not done anything to the controller as I’m not clear what the better option is. Trying my best to follow what you guys are talking about.

The only snag I see with running all the 12V logic from the battery is that if the battery died, or for some other reason wasn't available, then there would be no water movement at all; which the coral might not like (but I know zilch about coral, so Joe can advise if static water would be a problem).

My fear is with no water at all moving through the 100+ gallon filter, the stagnant water in the filter becomes putrid. When power is resumed, the fouled water enters the tank and the most delicate creatures die first, further fouling the water. That vicious cycle can crash a tank. Coral can handle a few days bumming out in water with very little movement.

The really loud "wake the dead" piezo draws 110mA. The other piezo I have draws 10mA. If it helps, I think the not so crazy loud piezo would do the trick. Shoot, if I hid it in the kitchen we'd hear it throughout the house. If it makes things easier, let's use the little 10mA buzzer.

The low ESR 470u caps arrived today, so I was going to start making clean copies of the PDM. I’ll add a diode at the LED and the 470u cap across the pump leads. Can/should the snubber at the pump leads be omitted? Should I hold off just in case the battery backup demands changes to the PDM?

 

[alec_t]

How, exactly would you want to power the alarm module?

From the 12V output of the battery backup supply.

My fear is with no water at all moving through the 100+ gallon filter, the stagnant water in the filter becomes putrid.

The backup supply for the filter pumps would prevent that. The other pumps, of course, would only run when the mains supply was present.

If it makes things easier, let's use the little 10mA buzzer.

Either would be ok powered from the backed-up 12V. Run time on battery would be extended by ~6% if the 10mA one were used, though; unless you were around to switch off the alarm or it had an auto-shutoff as KISS suggested.

Can/should the snubber at the pump leads be omitted?

I'd leave them in....belt and braces.

Should I hold off just in case the battery backup demands changes to the PDM?

The only PDMs possibly needing a slight change (connection points for the 20/12V supplies) would be those for the filter pumps. The other PDMs should be ok as is.

 

[ronv]

Joe,

I sent you a link for the parts for the charger. I hate to see you buy everything off of e-bay.

 

[salty joe]

Thank you Ron.

 

[salty joe]

For the tide and wave controlled PDMs, (that won’t have speed control) am I correct to omit terminal points for prolong, speedcon,and isense?

 

[KeepItSimpleStupid]

I sense is worth keeping. Being able to measure the voltage across the sense resistor easily will be worthwhile.

Still consider to make each module as identical as possible to allow substitution. i.e. Spares.

 

[alec_t]

I agree with KISS on both points. So maybe make at least one other PDM the same as for the filter pumps?

 

[salty joe]

OK thanks-will do. I was just looking to lose a boatload of wires and termination points.

 

[alec_t]

It depends how modular you want to go. There's also the current to consider. For the tidal pumps, two starting up simultaneously will draw ~9A briefly. If all 4 PDMs for that controller are on the same board you would need 9A-capable wire if all 4 were fed from a single Supply+ terminal, whereas 4.5A wire to each PDM would do if each PDM had its own Supply+ terminal. What is the current rating of the terminals?

 

[salty joe]

Wow, really good point on the pump load. I'll try to find out what the terminal points are rated for, in the meantime you changed my mind about combining power ground and 20V. I'll still have two PDMs on a board, but each PDM will have its own 20V and power ground. Thanks for that heads up.

 

[salty joe]

The terminal points have a 15A 300V rating. Whew, that's a relief. I'm still keeping a dedicated power and ground for each pump. Very much appreciate you having me check that out.

I'm starting on clean copies of the PDMs until the charger is ready to build.
Thanks a million.

 

[alec_t]

When they're all built it would be an idea to test them against each other without the pumps connected. Voltages at corresponding points in each PDM should match (more or less). Any 'odd man out' would be suspect. Good luck with the build.

 

[salty joe]

Thanks, great idea. Should I measure across Rsense, the V at all Q1, Q2, and Q3 legs that are not grounded, +pump lead, 12V, is that a good start? Any other points I should measure and compare?

Just finished the first clean PDM with the latest improvements. I'll get started on the next one tomorrow.

 

[alec_t]

Should I measure across Rsense, the V at all Q1, Q2, and Q3 legs that are not grounded, +pump lead, 12V, is that a good start? Any other points I should measure and compare?

All good. Perhaps also the junction of R11/R12.