Surge protector for Engel fridge?

[Wyowanderer]

I'll be ordering an Engel MT45 next week for my camper, but I'm a little spooked after reading the (admittedly few) comments about power supplies having trouble.

Edit: After rereading the previous sentence, I realized that it's a bit vague. What I'm referring to is the power supply or circuit board of the fridge. I've seen a few posts about folks having some trouble and having to replace them, and I'd like to do everything possible to prevent it in my new fridge.

My question is this: What device can I use as a surge protector between the fridge and battery to limit voltage on startup? My dual battery setup uses a continuous duty solenoid to isolate the accessory battery when the ignition is off, but I'd like to add a little extra protection during startup.
I realize that I could just unplug the fridge before startup, but I can imagine that it would become cumbersome in short order.
I'm looking specifically for something I can wire inline between the battery and fridge, if possible.

Ideas, advice?

 

[4x4junkie]

A large capacitor (or capacitors in parallel) connected (soldered) across your power cable near the fridge should do the trick. Any spikes or surges created by other devices operating would then be absorbed by the cap.

http://www.allelectronics.com/make-...-UF-50V-ELECTROLYTIC-SNAP-IN-CAPACITOR/1.html

Or you could use 2-3 of the 4700µF @ 25V ones in parallel at the bottom of this page:
http://www.allelectronics.com/make-a-store/category/140100/Capacitors/Electrolytic-Radial/1.html


Same application of capacitors:
I connected three 15,000 µF caps similar to the above where the battery cable is connected at the starter relay on my vehicle after I remote-mounted my battery to the rear. The cap eliminates the possibility of surges or spikes due to the long cable run from damaging anything (EFI system, my own fridge, etc.).

Hope that helps

 

[Wyowanderer]

Thanks for your response.
Can you elaborate a little? If I understand your post, I'll need to solder the capacitor across the positive and negative terminals. Is that correct?
Next question: is this something that is already made that I can buy?

 

[pods8]

What is the background here, when the truck starts it screws up your fridge since the solenoid connects your camper battery right away and it pulls current? Assuming so other options are you could just put a manual switch in on your solenoid and wait to connect it until you're running (chance to forget) or use an ACR or such that doesn't link them up until a high enough voltage is present and a minimum time has passed. Just more options for consideration.

 

[Wyowanderer]

What is the background here, when the truck starts it screws up your fridge since the solenoid connects your camper battery right away and it pulls current? Assuming so other options are you could just put a manual switch in on your solenoid and wait to connect it until you're running (chance to forget) or use an ACR or such that doesn't link them up until a high enough voltage is present and a minimum time has passed. Just more options for consideration.

I'm advised by an Engel rep that the main "warranty" problem they have is damaged PC boards due to voltage spikes, so I'm interested in preventing it from happening in the first place.
It could be that the troubles that are noted are due to electrical system problems, but at nearly a grand for the fridge, I want to take care of it the best I can. I'm pretty inexperienced with electronics so I'm looking for guidance.
What is an ACR?

 

[pods8]

What is an ACR?

Automatic Charge Relay (ACR), Voltage Sensing Relay (VSR), etc. are just relays/solenoids that require a miniumum amount of voltage to connect up the two systems. Thus when you start your vehicle the relay waits until the alternator is outputting at a steady state (and there is usually a little delay as well) before linking things up, thus your auxillary battery will never see anything in regards to the truck electrical system during the starting of the vehicle. Assuming that is something you're trying to accomplish that is one of the options in how to handle it.

 

[4x4junkie]

Thanks for your response.
Can you elaborate a little? If I understand your post, I'll need to solder the capacitor across the positive and negative terminals. Is that correct?
Next question: is this something that is already made that I can buy?

Correct, it would be connected or soldered across the power leads at the fridge (+ to +, - to - ). You could make yourself a short jumper wire a few inches long that has the capacitor(s) on it... Plug the jumper onto your power cord, then plug the fridge into the other side of the jumper.

What a capacitor does is stores an electric charge to act as a buffer against very sudden changes in voltage (such as the spikes created by your starter motor). You might be able to better relate to how it works in terms of the capacitor acting like a "flywheel" on your power cable. Sudden, brief power surges into it (spikes) will create very little fluctuation in it's voltage (or "speed").


Capacitors are available with screw terminals if you don't happen to have a soldering iron... I checked Ebay, they're all over the place there. Pricing looks to be around $7-15 +shipping for ones that would work for you.
http://www.ebay.com/sch/i.html?_trksid=m570.l3201&_nkw=capacitor+computer+grade&_sacat=0

Something between 10,000-22,000µF & 16-30 volts should work (it's value is not critical).
You can go higher too if you want, though they will also get physically bigger as well (there are guys who put setups as huge as 10,000,000µF (or simply 10 Farads) on their car stereo amps to smooth out voltage fluctuations because of their fluctuating power consumption! Your fridge wouldn't need something that huge however).

The automatic relay pods8 mentions sounds like it would do the trick also, however I don't think it would offer protection from other equipment running off the same battery, such as a 12V air compressor motor clicking on & off, for example (I don't know how sensitive the Engel's power unit is really... However I haven't really heard of people having that many problems with them).

 

[wrcsixeight]

If I utilized a solenoid for battery isolation, I would use the blower motor circuit to activate the solenoid, since that is unpowered during engine cranking, and would effectively isolate the aux battery from starter current

 

[Wyowanderer]

The electrical system on my truck disables all power when cranking except for the starter, and it lacks an accessory ignition position. I've wired the radio to work only in the on position, so I don't think it'll be a problem.
The solenoid for the spare battery is powered by the same circuit that supplies the electric choke, which is also unpowered during engine cranking.

Thanks to all. I'm off to build a box for a capacitor.

 

[kevint]

I'm curious regarding people's thoughts on this. Is this really needed if you have a 12v fridge? This seems like it would be a widespread problem that would affect fridges of every brand. I have been looking at fridges but had sort of considered them "plug 'n play."

 

[4x4junkie]

I did note above I have not seen widespread failures with fridges where it was actually determined a voltage spike or transient while starting the vehicle was the cause, however such failures in electronics usually are extremely random making it hard to pin down that a spike infact caused it (sometimes a device doesn't show signs of failure right away, either), so my thought was to simply play it safe much like you would in your house, plugging your computer, TV, DVR/VCR, etc. into a spike/surge protector (as the OP said, a fridge is a pretty good-sized investment, and typically has a fairly sophisticated electronic controller in it). Capacitors are only a few dollars to $20 max (plus a little of your time wiring/soldering it inline), so I see no real reason not to use one.

I had a Yaesu 2-way radio that was glitching fairly often while starting the vehicle (scrambling/resetting the display) that no longer glitches since putting a cap on it, so I know it does help.