rigger 47 Posted August 5, 2010 Share Posted August 5, 2010 island time PostPosted: Wed Mar 04, 2009 2:08 pm Post subject: Hoping someone out there knows a bit more about electric motors than I do. My autopilot pump is drawing more current at full load than it should. It is a Simrad RPU160, connected to a Simrad AC20 AP computer. The computer can provide 10 amps continuous, or 20 Amps max for 5 secs. The pump spec/manual says 17 amps at max pressure (60 bar). However, when the stern is shunted sideways by a wave, the AP fails with a current overlaod message. In the marina, as a test, I held the Wheel and the AP "port" button and can generate the same error. I then measured the AP pump draw while conducting this test. It drew 24 amps, which is why the computer complained and switched off. So, I see two possibilites. The pump is stuffed/worn out/damaged windings, OR the load on the rudder load is just to much for it. I don't want to buy a new pump ($1500 odd) if it is going to prove no different! Does anyone know what the stall load normally is for an electirc motor, compared to max working load? Or any suggestions how I may test this? I'm thinking of measuring the hydraulic pressure at the ram somehow, to see if the pump is actually producing 60 bar, but I don't have the gear for this... Suggestions? Thx Matt ======================================================================== wheels PostPosted: Wed Mar 04, 2009 4:06 pm Test it under no load and see what the current draw is. If there is a winding short problem, the current will be high even under no load. Plus the motor should sound to be running slower than usual. You shouldn't be able to stall the rudder yourself. The Ram will develop a lot of power measured in 1000's of Kg's. But it is also possible that relief valves are fitted (should be fitted) so you could actually be overcoming the relief point. Although that would mean they are set too low. The motor should be available as a spare. I would ask Simrad what the cost would be for motor replacement and if it is affordable, send it to them for evaluation. ======================================================================== island time PostPosted: Wed Mar 04, 2009 4:59 pm Hi Wheels, The no load consumption is a BIT high (8.3 amps, should be 7.5) There are relief valves in the pump body, but this is not what is stopping the pump - when you fix the wheel, activate the AP, and watch the amps - the pump is switched off by the computer. This is also confirmed by the error message on the AP. The more I think about it the more I think it is the pump motor. It is the combination of pump and supply (computer) that Simrad recomend. There is no indication of a problem with the computer. Surely the right pump should not be able to overload the supply... Cheers Matt ======================================================================== island time PostPosted: Wed Mar 04, 2009 5:05 pm Further to that, the only reason I can stall the rudder manually, is because the main steering system is mechanical and still connected - so I have a heap of purchase. There is no way you could manually stop the ram without that. It still takes a bit of strenght.... ======================================================================== wheels PostPosted: Wed Mar 04, 2009 5:35 pm Can you measure the voltage at no load and at loaded. Remember that the motor will have that current rating measured at a test voltage. Unless specified, it is possible the test voltage is 13.8V. The higher the Voltage, the less the current drawn. If the battery voltage is low, the current will be higher. 8.3A is not what i would have called high. In fact it is about what I would expect you would see at 12.5V. 13.8 x 7.5 = 103.5W divided by 12.5 = 8.28 The other point to check is the brushes. That is the major wear area. ======================================================================== island time PostPosted: Wed Mar 04, 2009 6:33 pm Yep, pretty much what I thought! Voltage was 14.2 when test started, dropped to 13.4 when drawing 24 amps... The test only lasts about 3 secs... The batteries are 120amp hour and fully charged (solar and wind). I appreciate your time... Matt ======================================================================== wheels PostPosted: Wed Mar 04, 2009 6:44 pm Hmmmmm. Well certainly check brushes. That part is easy and is the major wear part. At the same time, you can check the bearings for noise. If rumbly, they need replacing. The pump itself is so damn simple, I can't see it causing the problem. It is possible there is a blockage, but being an enclosed system, it's very unlikely. Normally if a bit of something does lodge somewhere, it is in the relief/non-return valves and causes creep. The brushes should be available as a part, bearings should also be but can often be found at a bearing shop. The motor should also be available as a part. The pumps tend to either work or leak. All the best on it mate. ======================================================================== island time PostPosted: Wed Mar 04, 2009 7:17 pm Sorry, should have put this in the last post. Brushes are ok, and I have just replaced the bearings and oil seals. I've asked Simrad if just the motor is available as a spare... Guess I ahve to bite the bullet and buy it to see if that's what the problem is. Hope it's not a waste of money! Thanks for your help. Matt ======================================================================== wheels PostPosted: Wed Mar 04, 2009 7:46 pm I wonder if they could send you a new motor with the view of returning if it doesn't solve the problem. Or if they have a known good second hand motor they could loan you to see if that is the issue. ======================================================================== island time PostPosted: Wed Mar 04, 2009 8:22 pm Yep, I've asked (via email just now) I'll see what happens.... ======================================================================== island time PostPosted: Sun Mar 08, 2009 6:26 pm Update. No motors in NZ or Ausy. Advance trident says "get one somewhere else if you can" or buy the whole pump from them ($2200 !!) The problem is that I'm not convinced the motor is actually faulty. The manufacturer of the motor has now given me by email the max amps of the motor at stall - 46.7 amps! So the "right" autopilot computer can only do 20 for 5 secs, or less than half the max. The spec for the pump says 17 amps at 60 bar - so tomorrow I'm getting a local engineer to measure the hydralic pressure at the pump to see if we are getting the 60 bar. If it is ok, there is nothing wrong with the pump. SO, what I propose to do is to connect the pump direct to the 12v supply using 2 Double Pole single throw relays - 12 v 50 amp, with a 50amp fuse on the supply side. My theory is that the AP computer will then only have to feed the coil side of the relays - a fairly small load that it should handle fine. The motor can then draw whatever it needs..... What do you think wheels? Cheers Matt ======================================================================== wheels PostPosted: Sun Mar 08, 2009 7:16 pm yeah that sounds like a good idea, However, Check that you don't have a user adjustable cut out or current setting on the Pilot. Many pilots have this setting because the pilot is brainless as to what pump you have fitted. So you should be able to set a parameter of max current. The setting may currently only be set to say 15A and yet the pump is drawing more. Normal operation would be fine but when the weather causes more demand on the pump, the pilot says no it will burn out the motor so I won't give it and set of the alarm instead. ======================================================================== island time PostPosted: Sun Mar 08, 2009 7:53 pm Unfortuantley there is no way to alter this in either the software, or anything that Simrad/Navico will tell be can be done. The RPU160 pump is the one recomended by Simrad/Navico for the AC20 computer that I ahve though, you'd think the factory would have matched them properly..... Cheers Matt ======================================================================== wheels PostPosted: Mon Mar 09, 2009 5:54 am That is indeed strange as my old Standard Horizon AP50 has that adjustment. I may be wrong, but I was under the belief that the SH became the Simrad. The adjustment on mine is on the PCB of the main control computer. I have two adjustments. One is overload an the other is max position of lock to lock. These are both small adjustment pots. There are also other pups available. $2200 is very expensive for a pump that size. I would shop around for other units to see what is available. At $2200, you may as well buy throw in an extra 1K ruffly and buy a new Navman package. (I think the cheap unit has a pump with that??) ======================================================================== Slacko PostPosted: Mon Mar 09, 2009 8:57 am If you go down the relay route, try to get some solid state ones rather than relays. Quieter, and they won't burn out the contacts if the outputs are switching on/off constantly with the motor loads. ======================================================================== Link to post Share on other sites
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