Alde fuse(s) blow upon shore power disconnect - WHY?

m_lewis

I have seen multiple mentions, here and elsewhere, that one is likely to blow a little glass 3.15A fuse or two on the Alde when disconnecting or sometimes connecting shore power to the camper.
Why?
Firm advice indicates one should always turn off the Alde before connecting/disconnecting shore power.
Some reports say it is the ground fuse, so running a separate ground from the Alde to the battery's negative post solves this problem. Some say both fuses blow, some say they never have had the problem.
My 2019 400 BDL camper (used) came with two spare fuses in a bag on top of the Alde connection box, so I am assuming that is stock configuration and they never blew. Or, the previous owner had the problem and left replacements handy.
I have on numerous occasions had the power fail and my EMS disconnected the shore power until it was again stable. I have also, either by fault or before I knew this was a problem, disconnected shore power with the Alde on, but most likely not heating.
As an electrical engineer, I find these circumstances difficult to understand. Why would an obviously well designed piece of equipment be likely to blow a fuse on its DC ground line when AC power is interrupted? Is this due to a design flaw, improper installation, a problem with associated equipment (the converter), faulty wiring in the camper, or perhaps the way some folks connect the shore power cord?
Could they be unplugging the shore power cord in such a way that the neutral line is broken before the hot and ground?
Does it only happen when the shore power breaker is not turned off before unplugging the cord?
Does it only happen when the shore power cord is first disconnected at the pedestal?
Proper disconnect technique is to first turn off the breaker on the pedestal, then disconnect the twist-lock connector at the camper, then unplug the cord from the pedestal. Proper connection sequence is breaker off, cord to camper, cord to pedestal, breaker on.
Does it only happen when the Battery Disconnect switch is in the Off position?

I would appreciate reports from anyone having direct experience with this problem, especially if they can recall the sequence used, whether or not the 1kw or 2 kw heaters were operating, and the status of the battery disconnect switch.
I don't want to awaken to a freezing cold cabin and have to take the bed apart to replace a fuse just because there was a power glitch.

MuttonChops

m_lewis said:

I have seen multiple mentions, here and elsewhere, that one is likely to blow a little glass 3.15A fuse or two on the Alde when disconnecting or sometimes connecting shore power to the camper.
Why?

. . . Firm advice indicates one should always turn off the Alde before connecting/disconnecting shore power.

. . . 2019 400 BDL camper (used) came with two spare fuses in a bag on top of the Alde connection box, so I am assuming that is stock configuration and they never blew.

My General Understanding:
  The original Alde Model 3010 had two 3.15A fuses on the main PCB. The Ground side fuse would blow most often if shore power was switched off while Adle was on however the ground side fuse also blew in non-shore-power switching situations. Adle / NuCamp never provided a technical description of why (as far as I know).  Adle / NuCamp did provide the grounding work around, extra ground wire to Adle, that solved most of the ground side fuse failures . . . however having Adle on when shore power was switched off could still blow fuse, just not as often.

The Alde Model 3020 which has been installed since December-2017'ish does not have the ground side fuse on the main PCB.  Model 3020 owners in general have not been having 3.15A fuse failures.

Expect your two fuses taped to Alde are the original factory spares.  My March-2018 build T@B with a Model 3020 also came with two shares . . . and they are still waiting to be needed . . .

Hope that helps.

pthomas745

Changed to slow blow fuse, hasn't happened to my 2017 in a year.

Sharon_is_SAM

I believe the consensus was that the fuse blew not from disconnecting from shorepower, but if the Alde was “on” when next plugged in to shorepower.  The surge caused the fuse to blow.  It happened to us following some upgrade work.  The A/C was not turned off.  When we hooked up to shorepower, the Alde ground fuse blew.  

vhollow

I have a 2018 400, towed with a Chevy Colorado. I too like to know the "whys" of problems, solved or not, and I attempted to provide at least a hypothesis in a long-winded post in Dec of 2018. Although, not being well-versed in the details of electricity, I erroneously characterized the electron charge that flows from the positive to the negative side of the battery. However, I will summarize my experience again here.

First, I should note two things: only a minority of owners seem to experience the blown Alde fuses, albeit a significant one; also, I always unplugged the trailer from both my TV and from shore power with the Alde turned off. Nevertheless, the ground-side fuse repeatedly blew. My hypothesis was that a micro-surge of DC current was traveling up the negative side of the Alde (wrong direction, looking for a ground) when the shore power was unplugged (Alde in off position, always). These are the three measures I took to solve the problem. First, I moved the ground connection from the Alde off the converter and directly on to the negative battery terminal. This move did not solve my problem. So I wondered if there was too much resistance in the negative wire connection from the converter to the battery, impeding the proper current flow from positive to negative and I increased the wire size from the negative terminal on the converter to AWG stranded 8, instead of 10. Interestingly, this did eliminate the fuse burn-out, as long as the trailer was still electrically connected to the TV, but not when it was unhooked. I inferred, or at least suspected from this, that the ground circuit from the trailer to the TV, along with my larger ground wire from the converter to the battery, was sufficient to prevent a surge to the Alde negative fuse. I also noticed that, unlike the practice in vehicles, my trailer battery and electrical system was not grounded to the chassis. In other words, the trailer battery used a floating ground system. I wondered if the negative side of this system, particularly when the battery was fully charged, was not "negative" enough to absorb all current from the positive side at the instant of shore power disconnect, allowing the surge to burn out the negative Alde fuse. So I grounded the battery to the trailer frame, and moved the ground wire from the Alde off the negative battery terminal and on to the frame ground connection. I have never had a problem since then. In addition, I was concerned that the chassis itself was not as good a ground as it could be (which might be why NuCamp didn't use it. This is because the chassis frame members are painted, then riveted together. I worried that the paint might prevent them forming a unified ground. So I bonded them, by sanding off the paint on a little patch of each side of their joined pieces, then wiring those points together. This bonding may well have been unnecessary, and increasing the wire size from the converter to the battery may also have been unnecessary. I don't know, because I did not test the chassis ground to just one piece of frame before doing these things.

I also really do not know if my hypotheses were correct. I just know that my problem disappeared when I grounded to the chassis and shifted the Alde ground wire to the chassis ground point.

m_lewis

@vhollow, interesting. My 2019 400 does have the frame tied to both AC ground and the battery negative in the converter. Perhaps nuCamp made a wiring change between the 2018 and 2019 model years.
As a rule, I like to use very stout busses for power and grounds, so I think your #8 ground-battery cable is good practice. When signals are ground referenced, any change in ground potential due to high currents in the ground buss can disrupt the signal, especially high frequency spikes.