Menu

Show posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.

Show posts Menu

Messages - J_Sail

#31
Upon further thought, a couple more tips:

1) I believe you would be very well served by a 100amp magnetic-hydraulic breaker of the type below:
https://www.bluesea.com/products/7144
or
https://www.bluesea.com/products/7187

Either should provide enough margin (and trip-delay-time) to avoid nuisance trips, but still provide reasonable protection against motor overheating damage if someone abuses it. The first one (187-series has a 5/16" stud and clearance to accept a 1/0AWG lug; the 285-series has 1/4" studs). Note that the delay curves shown on the two look more different than they are, due to different scales used. Both have better time delays than a Series-C breaker, which is less well suited to handle starting in-rush and momentary overloads.


2) Using your leftover #1AWG wire is a great idea. If you have enough for both the negative and positive runs in their respective colors that's great. If not, there is a very slight advantage to making the negative the heavier of the two. The windlass won't care, but when measuring voltages at various points, it's easier for a sailor to get confused when the drop on the negative is greater than the positive. On the other hand, it's even more important to follow proper color coding, so unless you want to do a lot of color tape application, the color of your leftover wire you have will dictate what it gets used for.
#32
Jon,
As you probably already know, you are free to put a larger breaker up to the ampacity of the wire, which is much higher than 70a. The only other consideration is that with motor loads (as I have posted before when discussing bilge pumps), it can be useful to have the breaker sized such that it will trip if you overload the motor so much that it's at risk of burning up its windings. Some motors have internal over-temperature protection, others don't. So if you call the manufacturer, you may want to ask if it is over-temperature protected, and if not, what they think is a good upper limit on a breaker to still get some protection against motor burnout if over loaded. For a 600w motor I would hazard a guess that 90-110a would be a good range to consider. (The manufacturer's tech support may or may not be sufficiently knowledgeable to help.)

Stu,
Yes motors draw much more current on startup (think back to the discussions of the short-term current for the starter motor on diesel engines).

In fact, motors draw more current anytime they are spinning slower than their no-load max rpm, whether it's due to starting inertia or mechanical load. When stalled (or starting from stationary) the current draw can easily be 3-10x. The wattage rating of a DC motor is for it spinning at full speed with no load. As you add mechanical load, the motor slows, and the current and wattage go up. So a 600w motor raising an anchor is going to draw more than 50A (and more than 600w) even after startup. I am not sure how much more Jon's winch motor will draw, though as I don't know how the winch is geared internally.

Jeremy
#33
Ron,
The info you refer to is basically what Jon quoted the manual. They may tell him more on a phone call, but they might just point to the manual. I think Jon is looking for additional guidance from someone experienced (hopefully an expert) who knows how much the motor will draw when starting under a load (i.e. anchored) and how much voltage sag is acceptable during starting. That would let him determine if he is okay with #4 AWG at his length or should increase to 2 AWG, with them commensurate cost, and difficulty in routing.

Regarding 3 AWG, Jon is correct, that is a common issue in converting from metric. For reference, each change of 3 gauge steps is an almost exact doubling in cross-section. Thus, 3 AWG is the same area as a pair of 6 AWG wires and is half of 0 AWG. So even though it is not commercially available, it is fine as a spec.

Hopefully MaineSail will see this and offer some sage advice.
#34
Nice work! I'm an old engine junkie and appreciate how much harder it is to work in such cramped quarters.
#35
Main Message Board / Re: New Traveler - WOW!
July 05, 2017, 03:48:44 PM
Ken,

Was that something along the lines of YBYC*?

* "Your Bed Your Choice"  ... Maybe better to not go there...


Your posts on bedding have been excellent. It's important for folks to understand that a paper-thin layer of bedding does very little good if there is any chance of even the slightest motion. Sealants rarely can handle thickness changes of over 50%. Given the thermal expansion/contraction over temperature extremes of sitting in direct sunlight and then cold nights, a paper-thin layer that gets squeezed to microscopic thickness when parts are expanded by heat, is unlikely to seal when things cool down. Modifying the interface to provide for a thicker layer of captive bedding is almost always a vast improvement.

#36
Quote from: Dancrosswis on June 27, 2017, 10:50:47 PM
Thanks for all of the great input.  I appreciate everyone's efforts. 
...
MPS-35.  Well, I never called it a MPS-50.   And, I only called it a MPS-150 once, before I wised up.  It is a MPS-35, designed for the Danfoss BD35F compressors.  Those compressors operate on either 12v or 24v, so my (limited) understanding is that the compressor will run fine on the MPS-35's 24v output voltage.  The MPS-35 has automatic power source switching (from AC to DC) built in.  No additional relay is needed.  The attraction of the MPS-35 was that it looked to be mostly plug and play.  But, if I don't need it to help my batteries--then I don't need it.

I mentioned the MPS-50 because the link you included took me to a page on the MPS-50, thus I asked about all three possible P/N's. As it turns out, though, it looks like the MPS-50 is just a slightly more powerful version of the MPS-35. More importantly, you are correct that the MPS does indeed include the relay built-in. I finally found the instruction manual online. Also, you are correct that the fridge compressor will auto-switch dynamically between 12v and 24v operation (I was concerned that it had to be pre-set to either 12v or 24v). So, it appears you could fairly easily add the MPS-35 to your setup.

As MaineSail correctly noted, it is true that some battery chargers will react to the on/off load of the fridge by invoking a higher-voltage charge cycle for some period of time. It looks like the Xantrex you have checks the battery voltage every 15 minutes, so hopefully that would limit the duration of any mis-provoked charge cycle. So, it's unclear if the potential benefit outweighs the extra complexity; you could go either way and someone will disagree!

As to proper float voltage, according to the manual I looked at, you can influence the profile by both selecting the battery type and the temperature setting (if you don't have the optional Battery Temp Sensor). Normally I would recommend the Batt Temp Sensor option, but I suppose it is conceivable you could instead set the temperature switch to HOT on the charger panel and get reduced float voltage at the expense of slower charging. That *might* make sense if your boat sits on the charger 24x7 with short sailing periods and the batteries rarely get run down much. (Caveat, I have not looked carefully at the numbers, so take with a grain of salt). As to which battery profile to pick, as MaineSail has said elsewhere, look at the voltages in the spec sheet for each profile and compare them to the specs of your specific batteries rather than assuming the names the charger manufacturer called them make sense. In your case, since Interstate is a re-labeler rather than a manufacturer it may be harder to get precise battery specs.
Your charger sounds like this one:
http://www.xantrex.com/documents/Discontinued-Products/TC20_40(445-0050-01-01_Rev-A).pdf
Look at the sections on Battery Temperature and the profile definitions in the Specs section.
#37
There are two separate issues being conflated here.
1) Your originally stated worry that running the fridge from your boat's 12v system while on the charger is bad for the batteries because it places a load on them.

2) John Nixon's statement that leaving your battery charger on 24x7 is bad for the batteries due to the small charging current created by the float voltage it applies.

#1 is a misplaced worry, as I explained in my previous reply. There is no load on your batteries when they are on the charger; the needed current comes from the charger.

#2 is a theory that I do not see espoused by leading experts in the field. I have not seen the study and research that John referred to. The leading expert in the yachting community seems to be Rod at Compass Marine (aka MaineSail) and his articles on selecting and setting up marine battery chargers and his extensive writings on caring for marine batteries do not mention it. My understanding is that the general consensus is that if one sets a quality modern marine battery charger to the float voltage recommended by the battery manufacturer, it is fine to leave it on the charger 24x7. It is true that many years ago it was not uncommon to find battery chargers with wildly incorrect float voltages, and too high a float voltage can shorten battery life. In my professional field (I am an electronics engineer) I have seen that problem with some computer UPS units that had float set too high, but not in any modern marine setups I have worked on.

You are making your setup more complicated, so I suggest you consider the extra complexity and the uncertainty surrounding any potential benefit before pulling the trigger.

IMPORTANT - Regardless of how you view the above, there are two problems with your plan that must be addressed.
1) If you are going to use a small DC power supply to run the fridge while on shore power, it should output 12-14vdc, not 24-27vdc. The unit you linked to says it outputs 24 or 27v. Hopefully it can be set to 12-14v, or it won't be right for your 12v fridge.
By the way, is it a MPS-35, MPS-50 or MPS-150? I think you have referred to it as all three at various points in your thread.

2) You will need a relay and additional wiring if you want the fridge to automatically switchover from your boat's 12v system to the separate power supply. That function is not built into the devices you have bought.
#38
Noah is correct, there is no need for an separate AC power module for your 12v fridge. That device is for owners of portable 12v fridges who want to also plug them in at home. There is no benefit on a boat with a shore-power battery charger.

When your battery charger is on, the power to run your fridge is coming from the charger, not your batteries. (Similarly when the engine is running it comes from your alternator.) That's because the charger or alternator puts out a voltage higher than the battery voltage (in order to charge it), thus the fridge simply slightly reduces the max rate of charge. It does not drain or in any other way, tax your batteries.  Also, you would need complicated wiring to accommodate it.

The IsoTherm, on the other hand, is a clever device that temporarily lowers the temperature setting of the fridge when energy is "free" from either the shore-power/charger or the engine running. It does so by detecting the higher 12v system voltage present under those circumstances (i.e. >~13v) and substituting its own thermostat. The idea is that chilling the fridge extra cold during those times, will cause it to cycle on less later, when you are on battery. If you are a cruiser whose use of engine or shore power fits the pattern it could be useful. If you have solar or wind power, though, it may be fooled into doing its extra-cool when you would rather have the solar charging your batteries. 

Jeremy
#39
And are you 100% certain they were not already sitting in the bucket, having gotten there from somewhere else?
#40
Main Message Board / Re: Fuse question
June 01, 2017, 12:12:37 PM
The short answer is a definite YES.

The primary purpose of fusing is to prevent the wiring from becoming a fire hazard in the event of an overload. The cause of such overload can be a failure in a device or a short circuit in the wiring (due to a breach in the insulation). Thus the wire to the bilge pump needs protection even though the only intended load is the pump. What if something like either a loose anchor or a sharp edge of a screw shorts the bilge pump supply wire to ground? In that scenario, the small normal draw of the bilge pump is no longer a factor, and the unprotected wire rapidly overheats and potentially starts a fire.

Thus the advice to size fuses/breakers (aka over-current protection or OCP) to protect the wire, not the load. The largest allowed amp value is a function of the gauge of the wire, the temperature rating of the wire's insulation, how many wires are bundled together, and whether the pathway includes an engine room or not. It is not a function of what the load normally draws. Those guidelines also allow one to slightly oversize the fuse in certain circumstances.

HOWEVER, there are limited cases where one MAY choose to undersize the OCP. One of those is for motor loads, where it might be nice to have a breaker that trips when the motor becomes temporarily overloaded due to something jamming it. In that case, there is a point of view that having a breaker that trips and can be conveniently/quickly reset may be better than risking the motor overheating and burning out. Some bilge pump manufacturers  provide a spec for such a breaker. In that case you may want to use a breaker that is smaller than the rating of the wire. If it's a fuse rather than a breaker, then I would probably not undersize it, as a blown fuse is almost as bad as a blown motor if you can't quickly find and replace the fuse.
#41
Main Message Board / Re: Fuse question
May 31, 2017, 10:15:30 AM
MaineSail's name is Rod, but mostly we just call him MaineSail; he doesn't seem to have taken offense yet.

Double-check your calcs and keep a spare fuse or two onboard, just in case, but you may well be just fine. If at some point you ever decide to fuse the #10 a bit higher, BlueSea does make an inline fuse holder that can take Maxi fuses as large as 60A (although the holder is rated at 48A continuous, so I would not fuse it above 50A). It has #6 pigtails, but could be readily spliced to your #10.
https://www.bluesea.com/products/5068/MAXI_In-Line_Fuse_Holder

I would encourage you to fuse your reserve battery too. It doesn't matter if it's almost never used, the concern is something somehow causing a short in its cable. That could occur from something hitting, cutting, or chafing the insulation somewhere or from a careless moment during servicing, with potentially catastrophic results. Unless you are severely limited on vertical height, it's trivial to add a BlueSea MRBF/holder right to the battery terminal.
https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A

If you have not yet read MaineSail's article, it (and all his others) are a valuable resource.
http://www.pbase.com/mainecruising/battery_fusing

Enjoy,
Jeremy
#42
Main Message Board / Re: Fuse question
May 27, 2017, 05:07:40 PM
All of those fuses should be there, but in my book the more important of the two is to have a fuse at the battery. Fortunately, if you have a little bit of headroom, BlueSea makes a Marine Rated battery Fuse and holder that mount directly onto the battery post.  Take a look at:
https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A

Mainesail has discussed them on his site and on various forums.
http://www.pbase.com/mainecruising/battery_fusing
#43
Main Message Board / Re: Fuse question
May 26, 2017, 02:48:06 PM
Quote from: KWKloeber on May 26, 2017, 11:40:38 AM
Quote from: J_Sail on May 26, 2017, 11:29:05 AM
Quote from: mainesail on May 26, 2017, 04:21:19 AM
In a good DC panel design there is always a DC Main breaker. Some builders put this breaker right at the battery switch, to follow the standard, and keep the battery switch as close to the batteries as possible.

I'm curious, in the case where the battery switch is at the battery box and there is a suitable fuse near the battery switch protecting the wire to the Main DC panel, do you consider it poor practice to not have a readily accessible Main DC breaker somewhere (breaker rather than fuse)? I realize it's nice to be able to use a breaker to turn off the Main DC Panel, and one could argue that there is a safety benefit to being able to quickly restore power to the Main DC Panel after an overload, but are either of those sufficient to warrant a breaker over a fuse in order to be considered "good design"? I know it's a judgment call, but I would value your professional insight.
J

Why not replace the fuse w/ a surface breaker, or thru-mount breaker next to the switch?  (seems best of both world's option)
Or leave the fuse, and put a switch only at the panel to disconnect the feed?
ken

Ken,
All of those are options, each with their own pros and cons. For example, the placement of a toggle circuit breaker in or at the battery box (which you present as best of both worlds) also opens the possibility of something inadvertently turning of the Main Panel, a risk not present with a fuse. These tradeoffs can be debated endlessly.

My posting, though, was specifically to solicit MaineSail's opinion as a leading professional in the field for his view of acceptable best practice.
#44
Main Message Board / Re: Fuse question
May 26, 2017, 11:29:05 AM
Quote from: mainesail on May 26, 2017, 04:21:19 AM
In a good DC panel design there is always a DC Main breaker. Some builders put this breaker right at the battery switch, to follow the standard, and keep the battery switch as close to the batteries as possible.

I'm curious, in the case where the battery switch is at the battery box and there is a suitable fuse near the battery switch protecting the wire to the Main DC panel, do you consider it poor practice to not have a readily accessible Main DC breaker somewhere (breaker rather than fuse)? I realize it's nice to be able to use a breaker to turn off the Main DC Panel, and one could argue that there is a safety benefit to being able to quickly restore power to the Main DC Panel after an overload, but are either of those sufficient to warrant a breaker over a fuse in order to be considered "good design"? I know it's a judgment call, but I would value your professional insight.
#45
Yes, you can parallel the two controllers feeding a single 20 or 25 amp fuse near the battery.

The actual point where you tie the two controllers to a single wire can be chosen for your routing convenience. Just make sure that at all points you use heavy enough wire to both keep within the safe ampacity of the wire (easy) and to also keep the voltage drop on both the positive and negative wires to a total of well below 3%. The lower the better, both to minimize losses in the wire and so that the controller's sensing of its output voltage accurately reflects the true voltage at the battery. Even relatively small voltage drops across the wiring from the controller to the battery result in less than optimum charging profiles. Don't go nuts over it, but increasing one size from whatever a wiring chart recommends for your length and current can sometimes be a worthwhile investment.

Also, my experience is that wiring runs are always longer than they look. So either measure or over-estimate.

If the wire run is 15 feet one-way, then using #10 wire (@1.0 ohms / 1k ft) for each panel and tying together near the battery, the total drop at 7 amps (peak output on a super sunny day) would be 0.105v on the positive and 0.105v on the negative, for a total drop of 0.21v, which would be great. If you tie the controllers together and use #10 for the two together then the drop would double to 0.42v (14 amps passing through the wire's resistance). That's slightly over 3% of 13.5v (a typical voltage while charging).

If you use a #8 (.6282 ohms/1k ft) for the two combined, though, your drop is only 0.26v (2%). 

BUT if your one-way distance is much more than 15 feet (which it could well be), you need to adjust the calculation.

Disclosure - I just did this calc quickly without much checking, so others on the forum should feel free to double check my work. You can also use an online calc, such as:
http://www.calculator.net/voltage-drop-calculator.html
Also I don't own a C34 so don't have a good gut sense for the wire length involved.

I used 7 amps as the max output from each controller based on a theoretical peak of 100w into a 14v load (battery during charging at twice that current due to two panels). The reality is that it is likely to be more like 5 amps (or less) per controller in real-life conditions. So if the wire gauge becomes a cost or other challenge, you can redo the calcs at the lower current.