Blown fuses.

[Maynard Rupp]

I'm a total novice with electrical issues, but can anybody calculate the load that those a/c systems SHOULD be pulling? Does it closely approach 30a? If the calc says no, as someone mentioned earlier there could be a prob with one of the a/c units.

It calculates to a bit over 30 amps. The ships ammeter shows 28 amps, so my calculations are about correct. Don't forget though, we actually blew a fuse with only one unit selected on. The other was turned off for at least 2 weeks. The larger unit, (the one operating), has a 20 amp circuit breaker in the AC panel, yet that breaker did not trip, the 30 amp slo-blo fuse went open.

 

[Maynard Rupp]

The heat from the fuses also melt the wiring behind the fuses and that aint a good thing!

I like your idea about the 50 amp. re-wire, but what would replace those fuses to protect the wiring from the plug to the ships panel? I removed the entire plate with the two 30 amp connectors. The backside and wiring looks like new with no signs of heat in that area, only inside the fuse holders.

 

[captddis]

What I have done is to have a new SS plate made with the breakers in place of the fuses. The breakers get silicone boot covers over them to be waterproof.
As a alternative you could have a seperate plate made for the breakers that would cover the fuse holes.
I use a single 50/ 125/250 cord. Once completed you will never have problems and you will never overload the cord.
I had 3 36c that I maintained and they always had problems with the AC line. On those Hatt only ran 10 ga wire to the panel and one charred the wire halfway to the panel! I believe Hatt put a bulletin out about changing the wire. On my 38 Bert the Ac line melted the plug while I was looking at it before I owned it. I converted it pronto.
Dave

 

[TedZ]

Am i wasting my time?

An AC unit does not pull constant amperage if there is something wrong with the compressor and it does not have to be that major. Low water flow, bad refrigerant filter, worn unit etc. etc. all cause high head pressure or a high draw and will cause a climbing amperage.

Get a tattletale clamp-on meter if you like so you know how high it gets when it blows and you don't have to stand there holding it. Checking an instantaneos reading with a clamp-on tells you what the ampacity is at the moment...worthless.

If you are blowing a 30 amp fuse with a rated 16 to 20 amp load something is broken! That is a lot to be over and you have fixed the obvious things. Get a meter or a logger and stop scratching your head.

Do not put bigger fuses in. Rewire a 50 amp if you want, but aren't you a little concerned that you are going to feed more current to an undiagnosed problem??

Sorry to be direct, but...

Ted

 

[Trojan]

Yeh! Go ahead and rewire for 50 amps. Just make sure you have plenty of insurance. Start by checking your line voltage, check the voltage when the ACs starts, each unit, check the amperage at start up of each AC, check the run amps. Breakers do not open at the exact amps as stated on the breaker. It is somewhat higher and they ARE delayed. That is probably why you are not loosing breakers. I think you have a low voltage condition with a high start-up current problem. Everything is working as it is supposed to. I have seen the same thing happen on other boats. The only thing that will possibly help is a little bigger amp fuse or a higher voltage. Fuses week-en when they are constantly operated at there rated value. Get someone near you that can check this for you. Don't use the meters on the boat. They are not accurate. Don't burn your boat up. If you see no corrosion, there must not be any. So that's not an issue. This is not rocket science. There are replacement fuse cartridges that you can put any fuse element into it you want. The caps screw off and you can put in any size fuse strip you want. What is the temperature of the power cord to the boat. It should be warm but not hot. good luck.


BILL

 

[Trojan]

10 Gauge wire is rated for 30 amp. continuous use.


BILL

 

[captddis]

I am beginning to wonder if I am wasting my time also. The fuses SUCK!!!
Take your 30a cable and run 20 amps CONTINOUS for 12 hours and feel the cable it will be warm. Do this for days at a time and it will fail. On the boats with the 50 amp fuses they get hot and burn at a continous 35 amps. We are talking Florida boating here. the air cond runs 24/7 often without cycling pulling a fair amount of amps CONTINOUS. All you great lakes guys do not have this, even when you use air it cycles and your fuses last.
10 ga may be rated for 30a, but you have 50 feet of cord and another 15 to 20 ft going to the panel= 70 feet. Maybe you are comfortable with this . I am not. I maintain about 60 boats , many Hatts they all have the fuse problems, except the ones I have changed over. If the air cond on Maynards boat was drawing excessive amps the 20 a breaker would trip!
Fuses have not been used in houses for 40 years, maybe it is time to update the boat as well. Do what you want, my way works and is safe.

 

[Genesis]

I never had problems with the inlet fuses on my 45C.

50A service, but we regularly overnighted and dayed aboard, and in the middle of August, both AC units plus all normal house loads (including things like the hot water heater) were on.

I never blew an inlet fuse. Not once. Nor did they get hot. We regularly pulled more than 30 amps continuous without problems.

Fuses are supposed to STAY CLOSED at RATED current. If not then something is wrong with the installation, whether its high resistance or something else.

Fuses went out of style in houses because its too darn easy to put a penny in the fuse box if you don't happen to have a replacement, and that's a great way to get a fire. Bypassing a breaker is a LOT harder.

 

[captddis]

I have never blown any on my 46 either, but all the A/C s and appliances are 220 volts. I have a hard time ever getting to 30a per leg. Usually 15 amp per leg with everything running. The boat in question has 115 volt units and is on the edge with both units running.
The thinking here defies logic! If you have a properly rated breaker, it IS safe! Not to mention better. Viking and Bertram saw the light years ago and went with breakers. Even Bayliner supplies their 32 footers with a 50 a cable as does Grand Banks on their 32 footer. I guess they better call their insurance companies too!
Hey I guess you guys can help keep Buss in business.

 

[Genesis]

Breakers are ok but I personally like the input fuses because they have a thermal component. Magnetic breakers, which are all that are rated for boat use, don't have that second level of protection.

Shore inlet fires are pretty common and can total your boat. I like the added protection against them that fuses provide.

 

[captddis]

I know that is the thinking on the fuses ,but hot hot hot fuses are as scary as a hot inlet or plug. My way of doing the 50A to retrofit the two 30's is to leave the 30 amp breakers at the panel, run new 6 ga wire from the inlet to the panel and use 35 amp breakers at the inlet. The cord never gets warm nor does the plugs. Cool connections = safe . Much like under propping your engines, It is never maxed out! Dave

 

[captadamr]

Hey Maynard,

Did you blow any fues in Ft. Pierce? We used the A/C for 18hrs each day in Ft. Pierce, and for 4 days in Fort Lauderdale and did not have a problem. (knock on wood). The PO gave me a box of fuses and told me it blows them allot, but i havent had a problem yet. Just figured I would give you the expericnce we have had since we have the same hull. But ours only has one unit.

Adam

 

[captddis]

I rest my case!

 

[SKYCHENEY]

If these fuses are such a problem, then how come Hatteras used them for so many years? When these boats were new, they did not have these issues, did they? I still think something else is wrong here. The fuses are not the problem, just a symptom. You need to find out what is causing them to blow and fix that first. We all know that these electrical systems were well designed. Don't go changing the original configuration until you are sure that you need to do so.

 

[Genesis]

If these fuses are such a problem, then how come Hatteras used them for so many years? When these boats were new, they did not have these issues, did they? I still think something else is wrong here. The fuses are not the problem, just a symptom. You need to find out what is causing them to blow and fix that first. We all know that these electrical systems were well designed. Don't go changing the original configuration until you are sure that you need to do so.

DING DING DING DING DING.

If there's one thing Hatteras did right, with high reliability, it was the electrical systems on their boats.

I've found very little to complain about in that area.

I've pulled in excess of 30A on Gigabite's inlet many times - its not that hard to do if you start cooking on a hot night with the AC running - without a problem. I could pop the breakers on the genset doing that on the hook tho - those opened at 33amps (8kw genset)

I like overbuilding, but if you're popping fuses on a 30A inlet with a 20A load I'm suspciious. And BTW, the nameplate ratings on electrical equipment are maximum load numbers, not typical. If you're actually pulling the "nameplate" rating on your AC compressors either its 100F out and you're cranking it HARD to try to get things reasonable or something's wrong - and probably the latter, especially if its persisting over many hours' time.

 

[Trojan]

Warm cables don't burn up because they are on 24-7. High amperage burns up cables. If the power at his dock side is not high enough. Changing to a 50 amp service is not going to change things. It's the fuses that are letting go. We may be up north but we had warmer weather in the month of August then you did. But I don't think that is the problem. From what he describes I would guess he has low shore power or marginal. If he had a corrosion problem it would have burnt at the trouble spot by now. I run 100 ft. of 30 amp shore cord and 2 1600 BTU A/Cs on a continuous basis with no trouble. Except when other people are on line with there Ac's and the voltage is below 105 volts. He could change to the 50 amp service and it may help or just move the problem farther into the boat. And like someone said. It may be his AC is going bad. An improper AC that short cycles could easily draw excessive current at start up. I think we are beating ourselves up. Until he gets some good readings nobody will know. I just don't want him to spend a lot of money an a hunch. I'm just guessing. I have been wrong before. I use a real nice line monitor that records and prints out any faults from the norm that you set. It will check to the .25 volt. I also have a clamp on amp probe. You can get one for around $100. bucks.


BILL

 

[captddis]

Yea I know Hatteras did everything right. Like unsealed penetrations under the pulpit or the blistering on bottoms They are very good but not perfect.
bragging about pulling 30 amps on a 50 amp system, wow that proves a lot.
I am sure Skys boat does not blow fuses he is in Michigan!
A few years ago I picked up a 46 Bert in Toledo Beach. It had too 50a/ 125 inlets in the boat going into the inlets were two 30a cords with a 50a end on them. When I asked for the proper cords, they said they never had a problem.
They would melt here using the air. And you got it I put a single 50/125/250 in.
My post was for Maynard. I am tired of arguing with you guys. I think you would argue with Santa on Christmas eve.

 

[Genesis]

Not in the least.

I said that I popped the 33A breaker on the genset several times, but never the inlet fuses on shore power.

I've pulled all the way to just under 50A before on Gigabite - its not really very hard to do. Get both ACs blasting, have the water heater on (which is a 110V connection) then go cook something on the stove and fire up a couple of the burners, plus warm something in the oven.

Now go look at the ammeter.

Don't try that on generator power.

Fuses are rated at 25 degrees Celsius. Typically they derate 0.2% per degree Celsius over 25C. This is not zero, but its also not huge.

30 amps @ 120V is 3750 running watts, or about 5 gross horsepower. Fuses are specified to open within 10 seconds at 200% of rating for fuses rated over 10 amps.

These are all "fast blow" specifications.

If you have motors on the circuit (and you do in a boat) then slow-blow fuses should be used. Motor starting currents can be up to 700% of their running load, and more importantly, if the voltage is insufficient under starting loads they can stall instead of start, which WILL blow the inlet fuses.

This is a good thing, because the atlernative is the potential for a fire or a destroyed compressor!

Bad connections in dock pedestals and inadequate wiring at marinas are all too common. I've seen LOTS of marinas where my "240V" service is under 200V. This is a major problem with AC compressors in particular as they pull far too many amps and run REAL hot under these circumstances.

ASSUMING THE BOAT IS NOT AT FAULT the reason he's popping inlet fuses is PROBABLY due to inadequate or corroded dockside wiring and/or short-cycling AC compressors. If you have two AC compressors with one running, and the second attempts to start, old-style compressors (that is, piston style - not scroll compressors) "hard start" and can require a surge of 400% or more of their running current. If this draw drops the inlet voltage to 90V, for example, the motor may not start, especially if there is still pressure in the system (e.g. it short-cycles). It will sit there "locked rotor" until the thermal protection in the compressor trips - this typically takes 5 seconds or more.

This is VERY COMMON on mechanical-stat Hatteras boats - there is NO PROTECTION AGAINST SHORT CYCLING ON AT LEAST ONE OF THOSE COMPRESSORS IN EVERY MECHANICAL STAT BOAT I'VE LOOKED AT.

An attempted short-cycle start with inadequate or marginal dock wiring is very likely to burn the inlet fuses. This is a feature - not a bug!

The fix is to solve the problem with short-cycling the AC compressors and if your dock wiring sucks either fix it or bitch at the people who need to do so. This requires either putting time delays in the trigger box (Hatteras typicaslly put them only in ONE zone where you have two compressors - usually the salon one) OR replacing the mechanical controls with electronic ones that have integrated short-cycle protection. This will prevent the compressor starting into a load, avoid the locked-rotor situation and stop the fuses from burning.

It will also stop your AC compressor from (eventually) burning up!

 

[Maynard Rupp]

You guys all have great ideas and thanks for sure. I am taking notes and will check all of this including the possibility of voltage to water ground. Low shore power voltage and rapid zinc loss are sure possible indications of problems. I will never understand why Hatteras used 2 30 amp connectors instead of a 220 volt 50 amp system. I will bet they could have saved money also and you wouldn't need two cords. It is very true that there sure is a difference in problems between the Great Lakes and Florida. Wow. Our first anodes looked new after 20 years. We almost never used the AC units except for heat. One thing that does seem to be working great so far is our bottom paint. You southern folks put that thick crap on with a mop in hopes that more is better. We are using VC-17 which most say won't work in salt water, but so far divers say they are amased. The big advantage of this stuff is no build up what so ever. We re-coat annually, although some go as long as three years. The stuff is as thin as acetone. I will tell more later about this stuff. We need more exposure to be sure of ythe advantages, but, so far, so good.

 

[Maynard Rupp]

Thanks again everyone. Our first look will be an AC guy to check our 16000 btu salon unit. We ordered a "guppy" to help with our anode eating problem. I will do all the voltage to ground tests when I get back to Florida in January. If the AC unit checks out OK, and I suspect it won't, I will continue with the recomended tests..Thanks guys!!