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Old 12-05-2019, 03:51 PM   #1
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Surge Protection: A Seriously Technical Discussion

Having just acquired a new-to-me trailer I've joined irv2 and I've started thinking about surge suppression and energy management. In particular I'm toying with the idea of building my own system using an Arduino, or Rasberry Pi for the EMS part.

The first thing I'm investigating is the surge, or transient protection part of the problem. After looking around the forums I've decided that, for some reason, no one uses whole-house systems in their RV's. I would think they'd be easy to wire in, or perhaps even plug into empty breaker slots. Anyone know of any reason not to use one of these? Many of them are waterproof like this $70 Intermatic model. One advantage of these devices are that they're UL 1449 certified (meaning they're not supposed to catch fire should the MOV's fail). I don't think any of the RV surge protectors meet this particular certification. Another advantage is that you can pick them up at your local big-box hardware store. They obviously don't deal with over/under voltage conditions, but that's mostly a separate problem.

While there are a number of technical articles and app notes on using MOV's and other devices for surge protection, there don't seem to be any suitable DIY designs for 30A or 50A RV service, so I'm trying to come up with one, not just to save money, but because if I build it, I can repair it.

As part of my research I looked at pictures of the Progressive Industries EMS-HW series of converters. I don't have one, but from pictures I've found their design raises some questions. For example, the thicker MOV's that they use (at least the ones I can see in pictures) are 20D122K and 20D122KJ. These are 1200V parts! They obviously do the job, but the varister voltage is much higher than I would have expected for anything other than between L1-L2 in 50A service. Anyone else surprised by this?

I also can't figure out PI's surge ratings. For example, the MOV board when populated for 30A use has a total of four MOV's, two thick (PN above) and two thin. The thick parts with a J rating have a Joule rating of 680J and an amp rating of 10,000A. I don't know what the thin parts are, but I doubt that they have higher ratings, so adding the likely ratings for all four parts would give 40,000A and 2720J whereas the product specs are 44,000A and 1790J. There is another MOV on the digital board, perhaps it's included in the specs.

The one other thing I've noticed is that there's no thermal or fuse protection that I can see on the thick MOV's. I suspect that the two thin MOV's are in a parallel configuration and that there might be a thermal fuse I can't see in the pictures. On the 50A version there are two sets of thin MOV's and I can see what looks like a thermal fuse next to one of the sets.

Most of the reference designs I've found protect every MOV with a thermal device or a fuse. I'm not sure that is required on the N-G MOV as the EMS will not allow large voltages on that pair. Littlefuse has an MOV with a built-in thermal device called TMOV that only cost less than $3 each. Even if I put 3 in parallel across all three circuits it would cost me less than $30 in parts.

Let me know if you know of a robust, and safe surge protector design that's suitable for RV's, or have thoughts on how one should be designed. Given campground wiring and long power cords, short of a direct lightning strike, I don't think super-fast transients are going to be much of a design consideration. Also, when factoring in the EMS part, and depending on the switching speed of the contactor relay, it may be possible to use the contactor to protect agains lower voltage surges (e.g. TOV's or temporary over voltages). Perhaps that's why PI can use 1200V parts.
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Old 12-05-2019, 04:07 PM   #2
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Surge protection, like lightning transients or voltages high enough to blow out a MOV, are not the typical RV electrical issue. In my experience low voltage and open grounds are much more common.

A Progressive HW protector (or a Surge Guard, aka Southwire, protector) both offer an array of electrical fault detection that household units like the Intermatic do not.
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Old 12-05-2019, 05:57 PM   #3
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I would think it would be much simpler to just purchase a Progressive or Surge Guard product and it may even turn out to be cheeper that buying all the parts and making one yourself, especially if you factor the value of your time.
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Old 12-05-2019, 07:42 PM   #4
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I use the TRW 35550 30 Amp RV service hardwired surge guard, commonly available for around $ 190 plus sales tax. Quite a comprehensive set of features, I think it's well worth $ 190 ...

Normally Open 30 Amp DPST Hot-Neutral Industrial Contactor Inside
Hot-Neutral contactor opens or stays open if one the following conditions exist:
- less than 102 volts on input (must be less for over 8-14 seconds)
- more than 132 volts on input (must be over for over 8-14 seconds)
these will block immediately on end of power up startup 128 second delay
- open ground
- voltage on ground (I understand the threshold is 3 volts)
- Hot Neutral Reversal
- less than 128 seconds has elapsed since power applied to input and no
other conditions exist ( this is to protect compressor motors against
power interruptions )

H-N , H-G , N-G surge protection with 6500 A max spike current MOVs

Green/Red Line voltage LED and Green Solid/Flash delay/caution LED
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Old 12-05-2019, 07:50 PM   #5
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Quote:
Originally Posted by bob26rls View Post
After looking around the forums I've decided that, for some reason, no one uses whole-house systems in their RV's. I would think they'd be easy to wire in, or perhaps even plug into empty breaker slots. Anyone know of any reason not to use one of these?
With all due respect, what do you think the Progressive and SurgeGuard devices do? Some are purely surge suppressors, but the more popular units have surge suppression and EMS combined into a single device.

As someone else already has posted, the need for EMS protection is generally greater than the need for simple surge suppression.
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Old 12-06-2019, 04:32 PM   #6
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I agree, brownouts and poor pedestal wiring are going to be more common than lightning surges. That's why I plan on using an Arduino or Raspberry PI SBC to monitor the voltages and connection conditions and to control a contactor relay accordingly. That said, surge protection is still important.

My hopes for this thread were that we could have a technical discussion about surge suppression in RV's. RV's are different. I'm still trying to decide, in the context of surge protection, if an RV is a house, or just a giant power strip with a really long cord.

Surges (or transients) are generally less than a few milliseconds in duration -- too short to allow protection by disconnecting with a mechanical relay. By comparison, one cycle of 60 Hz is ~17msec in length. That's where the MOV's come in. They can react in nanoseconds. Large surges are rare, but very destructive. They can come from lightning, a power pole being knocked down, or a transformer failure. In an RV park, the smaller surges, which may be quite common, are likely to be caused by RV's being plugged in, or unplugged, auto-transformers being disconnected, motors (e.g. well pumps), or even your own AC cycling. Basically anything that changes the load suddenly, or has a magnetic field that will collapse when disconnected can be a source of surges.

As has been suggested, I could just buy something, but what would I be getting? By itself, the Joules specs are meaningless. They're a money spec, just like amps is the money spec for vacuum cleaners. You're supposed to believe that more Joules = better and spend accordingly. It's worth noting that Joule ratings aren't part of any standards.

Neither SG or PI state what the pass-through or clamping voltage is. That's the voltage that gets through to the stuff you want to protect during a surge. The current ratings, when available, are probably just the sum of all modes as that gives a bigger, more impressive number.

I've noticed that MOV's with higher clamping voltages tend to have higher Joule ratings. The 20D122KJ MOV part numbers in pictures of the EMS-HW30C have a clamping voltage of 2010V. Yes, over 2kV! That doesn't sound like much protection to me. I don't know what the part numbers are for the thin MOV's that are probably protecting the L-N mode. Hopefully L-N protection is 600V or less, but we don't know.

Using higher voltage parts can help a manufacturer in two ways. First, the higher Joule spec as just mentioned, and second, fewer warranty claims. The MOV isn't going to degrade as quickly in the presence of the much more common lower-voltage surges. The Joule spec usually relates to how much energy an MOV can dissipate -- once. For smaller-energy surges, it's more like death by a thousand cuts. Over time the MOV's degrade and then fail, often failing when it doesn't seem like anything big happened. It was just the 1000th cut. It didn't need to be a big surge.

So, I guess the question I'm trying to answer is what specs do I want in a surge protector in an RV? Once I know that I can start picking MOV's (or buying something with more complete specs).

Here are the typical parameters and reasonable ranges:
Code:
Maximum Continuous Operating Voltage: 150Vrms
Voltage Protection Rating (Clamping Voltages):
   L-N,L-G, N-G: 300-700V ?
   L-L: 500-1200V?
Max Discharge Current per mode: 40-100kA?
Nominal Discharge Current per mode: 3-20kA?  (can survive 15 surges)
UL 1499 certified:  Yes if purchased.
BTW, I've come to one new conclusion about whole-house circuit-breaker style SPD's (surge protection devices). They won't work well in RV's because they only protect the L-N mode, which is may be OK for many home panels where G and N are often the same thing. Not true in an RV.
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Old 12-06-2019, 05:56 PM   #7
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Originally Posted by bob26rls View Post
My hopes for this thread were that we could have a technical discussion about surge suppression in RV's.
You seem to be having a conversation with yourself as it sounds like you're trying to impress with your technical knowledge.
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Old 12-06-2019, 06:32 PM   #8
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Quote:
Originally Posted by bob26rls View Post

Let me know if you know of a robust, and safe surge protector design that's suitable for RV's
Surge Guard and Progressive both have a series of units that fit this bill. Reventing the wheel is not why the majority of us purchased RV's. Buy one off the shelf and relax.
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Old 12-06-2019, 08:46 PM   #9
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You seem to be having a conversation with yourself as it sounds like you're trying to impress with your technical knowledge.
Well, TechWriter, you're wrong. I'm hoping to engage in a stimulating discussion with other technical people who have a similar interest. That's why I titled this thread "Surge Protectors: A Seriously Technical Discussion". Instead, I seem to have attracted a bunch of replies from people who just want to offer me advise on what to buy.

Quote:
Originally Posted by spdracr39 View Post
Surge Guard and Progressive both have a series of units that fit this bill. Reventing the wheel is not why the majority of us purchased RV's. Buy one off the shelf and relax.
spdracr39, you might familiarize yourself with the history of Progressive Industries. That company wouldn't even exist if the founder followed your advice directive.
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Old 12-07-2019, 01:50 PM   #10
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Surge Protection: A Seriously Technical Discussion

I was a power, motor, mainframe computer, PC geek/guru, plus whatever tech for 40 years.
I understand what my Progressive Industries EMS does, how it does it, and how many times it has saved my RV stuff.

I now choose to not understand the stuff, but just trust it.

Arduino or Raspberry are small and inexpensive devices. Thatís just fine! But having everything in a single, totally effective package is too simple to ignore.

My PT-50C is about 10 years old. It owes me nothing.
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Old 12-07-2019, 05:29 PM   #11
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I think most of us on here trust the EMS series from Progressive Industries to fully protect our rigs, no matter what the problem is. I don't worry about the technical aspects of the unit are, as long as it does the job! JMHO
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Old 12-07-2019, 05:34 PM   #12
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I think most of us on here trust the EMS series from Progressive Industries to fully protect our rigs . . .
. . . or from Southwire (Surge Guard).
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Old 12-07-2019, 05:39 PM   #13
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. . . or from Southwire (Surge Guard).
Does SurgeGuard have one now equal to the EMS PI? And if so, do they give a lifetime warranty?
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Old 12-07-2019, 05:45 PM   #14
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To the o.p.


As I think you suggested earlier- under and over voltage situations are more common than damaging surges. So, If I were to to it again it's likely I'd buy an Autoformer that now also includes other protections as well....in a customer- replaceable module. However, I currently have a Progressive unit that has been very dependable with great customer service to back it up. The discussion is interesting though.
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