Can someone explain this electrics question?

[gjgm]

The engine hatch is on two rams. I do not know quite how they work, but I assume they are self contained units as there is only power cables (not hydrolics) going to them.
After the boat has been on the hard and not on shorepower, the rams will not work, until there is shorepower connected for 15 mins or so.This weekend, I had the fridge on, again no shorepower, and again, the hatch will not open. If I put the boat on shorepower for 15 mins, then I can hear the relays for the rams now stuttering, and if I leave it a bit longer..all is fine.
The "green light" is on all batteries, but I do not know how good a guide that is.
So, I assume that there is a voltage drop somewhere, but why if I connect to shorepower is there then not instantly enough voltage to the relays to drive the engine hatch?

 

[wofforduk]

might be worth checking your batteries, as a fridge will only draw 5a or so. best way is to get a voltmeter, and ckeck the voltage on your batteries and just before the relays, and have a friend operate them. you will see whats going on pretty quickly - ie if the battery voltage does not change but the relay does then its excessive volt drop, or if the battery voltage drops like a brick then your batteries could be flat/dead.

IMO its a case of taking some time to find out whats going on with your meter - but i would be suspect of your batteries

 

[SEARANGER ANCASTER]

might be worth checking your batteries, as a fridge will only draw 5a or so. best way is to get a voltmeter, and ckeck the voltage on your batteries and just before the relays, and have a friend operate them. you will see whats going on pretty quickly - ie if the battery voltage does not change but the relay does then its excessive volt drop, or if the battery voltage drops like a brick then your batteries could be flat/dead.

IMO its a case of taking some time to find out whats going on with your meter - but i would be suspect of your batteries

Would agree , sounds like a battery problem

 

[Neil_Y]

You can also loose Volts through corroded/bad joints so if there are any electrical connectors that you can take apart clean and bolt up again this might help, but sounds like your batteries might also be the problem.

 

[gjgm]

You can also loose Volts through corroded/bad joints so if there are any electrical connectors that you can take apart clean and bolt up again this might help, but sounds like your batteries might also be the problem.

Yep, tried that, thanks. I have been given a possible explanation offline. If the charger is already running at capacity (ish) then an extra load has nothing to grab from the charger, the power not being available from the batteries. That sort of makes sense to me, as a layman. Still, I am a bit surprised as all three batteries are fairly new, though it may only draw from the house battery. I have'nt tried the emergency start option that connects the engine batteries. A possible explanation, as I know the Webasto and Wallas units are very sensitive to adequate voltage so maybe the rams are too. Once I am using the boat regularly again, I don't seem to get this problem. Well, hopfully !

 

[Jegs]

Mechanical?

If they work during repeated use, might there be friction problem in the ram/s?

John G

 

[wingless]

It sounds like a battery problem.

The ram hatch lift is usually a motor driven lead screw, like from Hardin or from Lenco.

 

[gjgm]

It sounds like a battery problem.

The ram hatch lift is usually a motor driven lead screw, like from Hardin or from Lenco.

Ah, interesting thanks. That sort of concept, the whole unit seems to be inside the ram.
Right, I will try to test the batteries-I guess the house battery is low on juice. There are 4 relays inside an IP box and alot of wiring, but maybe I should spec a bigger battery next time...

 

[Alpha22]

When you charge up your batteries on shore power, how long are you leaving them on for? 15 mins may well be enough to get the rams working, but it is not fully recharging that batteries in that time. Have you tried leaving the charger on for a day or two. Then trying the rams a few days later??

 

[gjgm]

When you charge up your batteries on shore power, how long are you leaving them on for? 15 mins may well be enough to get the rams working, but it is not fully recharging that batteries in that time. Have you tried leaving the charger on for a day or two. Then trying the rams a few days later??

Everything works fine, other than the rams. What I meant was that it only seems to needs 15 mins on shorepower for them to function again. I hope I only have this problem at the moment because the boat is sitting around unused (water pump leak); once it is back in normal use (and here I assume the batteries are then in better fettle) then I have not had this problem.
Really I was justcurious as to why putting the shorepower on did not immediately supply enough power.

 

[septiclecky]

Are you still connected to shorepower when you operate the rams, if so you may well be using the shorepower to drive the rams and not the batteries.

 

[gjgm]

Are you still connected to shorepower when you operate the rams, if so you may well be using the shorepower to drive the rams and not the batteries.

I am concluding that if the house battery drops in voltage too much, the relays don't function. Connecting shorepower does not bring an immediate solution, though leaving the battery to charge seems to resolve this. Once adequately charged, the rams work both with and without shorepower. In my ignorance, I would have thought that conncting the shorepower would immediately supply enough voltage to the relays, and did not understand why the battery needs to recharge. The suggestion made to me was that if the charger is already supplying its full capacity to recharge, then it will not be producing some "excess" to power the relay/rams. Once the charger has spare capacity(or the battery now has a high enough voltage) all works again.
At least, I think that might be the explanantion if it makes sense to someone more familiar with this than me !

 

[wofforduk]

Yep that sounds about right, that if the charger is already providing as much as it can, there is none left to power the rams! Id be thinking of doing a drop test on your batteries, unless there is an unknown load that is slowly dragging battery power down!