Battery charger with no batteries: crazy or what?

[MapisM]

Everyone here seems to be ignoring the safety aspects of having some old knackered batteries on board that should IMHO be dumped - NOW
Duff batteries can cause huge damage and batteries (in general) should be respected.
You say that the old ones are getting hot - I bet they are bulging as well - IMO they need throwing out ASAP

Nope Hurric, since I disconnected them the other day, they are all as cold as the surrounding environment.
If they would keep overheating forever with no charger, my next boat might well be a Benetti, courtesy of the royalties on the discovery of a free and perennial energy source...!

Otoh, I agree that I could as well remove them from the boat, but I was thinking to do that when they will be replaced.
What sort of problem do you think they could create, just by laying there disconnected for some weeks?
I never heard of batteries cracking/leaking/exploding, unless overheated.


Re. the two schools of thoughts, I'm in the same camp as you are.
I always used cheap lead acid - actually not the cheapest, which would be the STARTING batteries designed for high CCA but not deep discharge, but the cheaper DEEP CYCLE batteries I can find. And I never had any problems with them.
Ok, with the current set I pushed my luck a bit, 'cause I should have replaced them at the beginning of the season, and decided to see if they could last for another summer, which they eventually did - well, almost!
So, I'm not so intrigued by lythium, TBH. Also because the lower space/weight is not so relevant, in a displacement boat like mine.

 

[MapisM]

Having read the notes on Victron site and though some more, I agree it can probably handle it. A well discharged set of batteries would take a straight 50A for several hours, so 30 seconds powering passerelle shouldn't bother it too much.

Thanks Anders, that's pretty much what I was thinking, but it's nice to know that I'm not missing something.

 

[Hurricane]

So, I'm not so intrigued by lythium, TBH. Also because the lower space/weight is not so relevant, in a displacement boat like mine.

Ahh - yes - but just think how much capacity you could have if you filled your current lead acid space with Lithium!!

 

[Beyondhelp]

Thanks for your warning, but I'm not sure if you saw my previous post where I confirmed that after disconnecting the batteries and running on the charger alone, apparently everything was working fine.
And still is, after almost two full days, by now. I mean, the charger never overheated, and it's handling the DC demand of everything I'm interested in.
The only inconvenience, as I previously mentioned (but which I can only notice because I know what I did and I'm keeping an eye on the instruments) is that when the higher absorption equipment (like the passerelle or the fresh water pump) start, it takes a second or two before the charger increases the current supply from say 5 or 10 Amps to 40 or whatever is required.
And in that second, the voltage drops below 20, and the passerelle obviously starts moving very slowly.
But it really takes close to nothing before the charger increases its output, the voltage comes back to normal, and the passerelle moves normally.

Are you suggesting that this could ruin the charger, and/or some other equipment? And if yes, why?
Thanks in advance.

Ok Sorry I didn't know if I got in soon enough. Usually I read the full thread unless I see something I consider potentially dangerous/hazardous. Put really simply unregulated battery chargers can produce with little or no load much higher voltages than would normally be seen when attached to a battery (alternators can do the same too). Now I'm not familiar with your charger and it would be crazy to design such an unregulated charger to a boat as it would shorten the life of the batteries significantly, but with the chances of damaging anything potentially far more expensive I felt the need just to jump the queue and say be careful, especially since you said the batteries were getting hot (really not good).

However if you have since been running without them anyway, and if via the battery monitors you are seeing nothing strange or unusual, then its safe to assume that the charger is regulated and in fact is capable (just) of the job you are asking.

The other problem you mention is also the kind of thing I'd expect to see with a power supply with inadequate output stability. That's to be expected if its intended for connection with a battery bank. What that means is that normally, a fairly brutal power supply would have a large bank of capacitors on its output. This stops sudden surges in load from causing the voltage drops you are seeing. DC motors draw a lot of current when they initially turn on, I would guess perhaps 4-5 times their normal running current. These can in worse case scenario cause a power supply not intended for this kind of usage to trip out entirely for a split second, resetting anything sensitive connected to it. The other side effect you can sometimes get is buzzing or humming in audio kit if a power supply is not properly filtered without a battery load attached.

 

[MapisM]

Aha, understood, all makes good sense.
I'm not so worried about sensitive stuff, 'cause as previously discussed the only equipment which might fall in such category is dash electronics, and I don't actually need any of that, for the remainder of the season.
But thanks for highlighting/explaining the logic, I appreciate.