Low volt sensor for 12 volt cooler

[Refueler]

Your idea ofan additional charger is not so bad. I think that I might be able to manage that. I can simple put a 240 v switche into the system & power up the main charger for a while each day or when I arrive in port & plug in the other charger once I am up to full power. If the domestics do run down the cool box will shut off & the start battery will also isolate via the VSR that i have betwen that & the domestics. The batteries are all AGM by the way
I now need a suitable charger that will not burn out on constant load & will just provide the 3.5 amps.

You will have to make sure the second charger does not feed into the other charger on the battery side.

I would put the switch on the battery side - because whichever charger is not connected to battery will be effectively 'off' anyway.
The 240v side can be left connected ..
Simple A - Off - B toggle switch in the +ve leads of the chargers is enough. That way you have complete simple manual control of which charger to use ...

 

[Refueler]

If the above does not solve the problems try one of Refueller's novel solutions

Tks Vic !!

I'm just trying to find simplest answer ......

Given that a cheap bog standard simple charger can be had for about a tenner .... and should just about balance out with the coolbox ... - seems easiest way to do it.

The trick of course is to not have charge rate higher than the coolbox requires .... or at least try to stay as close to it as possible.

 

[VicS]

You will have to make sure the second charger does not feed into the other charger on the battery side.

I would put the switch on the battery side - because whichever charger is not connected to battery will be effectively 'off' anyway.
The 240v side can be left connected ..
Simple A - Off - B toggle switch in the +ve leads of the chargers is enough. That way you have complete simple manual control of which charger to use ...

This wont matter or do anything detrimental surely. You don't normally isolate a battery charger output connection when other charging systems are in use. I would switch the mains inputs.

 

[Daydream believer]

14.7 volts for the absorption stage is rather high. It may be OK for lead calcium batteries but it is too high for other types. It would be unacceptable for Gel, AGM and sealed low maintenance batteries. Even with open flooded lead acid it would cause excessive gassing leading the need for frequent topping up. The gassing could cause the gas detector to alarm if not vented externally. This would be a nuisance , especially at night.

Your Dolphin charger should have several user selectable charging profiles. You could select one with a lower absorption voltage ( eg for FLA or for AGM ) You will still have the charger stuck in absorption mode rather than reducing to a float voltage of 13.2 or 13.7 depending on the battery type selected but maybe it will be a tolerable situation.

Your Dolphin charger may also have a "night mode" switch . This will allow the charger to operate at a lower maximum current without the fan running. Using the night mode option would solve the problem of the noisy fan at night.

The 3.5 amps taken by the coolbox will not be sufficient to prevent the batteries "overcharging"

If the above does not solve the problems try one of Refueller's novel solutions

The charger does not have any switching options.The supplier of the batteries ( Alpha batteries) confirmed that the voltages supplied by the battery charger under normal charging ( without the coolbox) was Ok. . I tried the charger on the old batteries when they were flat( AGM)& it followed the charging regime specified for the new ones. ie 2.5 hours at a lower voltage, then ramping up then dropping down etc . So it matches the spec sheet for the new ones Ok.
The charger fan only runs when the charger is putting in a lot of charge. Under normal use it goes off fairly quick. & the voltage drops
It is the cool box that b..gers the process up & keeps the fan running & voltage high.

 

[Daydream believer]

This wont matter or do anything detrimental surely. You don't normally isolate a battery charger output connection when other charging systems are in use. I would switch the mains inputs.

Switching the charger 12 V side becomes a problem because it has 2 wires. one to the start battery & one to the domestics so i would have to switch both

 

[Refueler]

This wont matter or do anything detrimental surely. You don't normally isolate a battery charger output connection when other charging systems are in use. I would switch the mains inputs.

With my simple old fashioned charger - they usually are based on coil wound iron cores ..... so leaving it connected battery side will have a small drain through it.
The more modern Dolphin charger _ I do not know if thats solid state or coil wound .... so I assume better to isolate on battery side to avoid any current going to it from the other charger.

I agree that we tend to leave charger systems in place on boats ... but check out as example a Carver panel in a Caravan .... it has a definite panel switch to isolate charge side from car vs charge from charger powered by mains ...
The power side was unswitched ... it was always on the battery side ...

 

[Refueler]

Switching the charger 12 V side becomes a problem because it has 2 wires. one to the start battery & one to the domestics so i would have to switch both

Then leave them and switch the 240 ....

 

[VicS]

With my simple old fashioned charger - they usually are based on coil wound iron cores ..... so leaving it connected battery side will have a small drain through it.
The more modern Dolphin charger _ I do not know if thats solid state or coil wound .... so I assume better to isolate on battery side to avoid any current going to it from the other charger.

I agree that we tend to leave charger systems in place on boats ... but check out as example a Carver panel in a Caravan .... it has a definite panel switch to isolate charge side from car vs charge from charger powered by mains ...
The power side was unswitched ... it was always on the battery side ...

Yes it will but not anything to do with the iron cored transformer but rather due to the old fashioned rectifier that it contains.

( Back current through an old 1¼ amp trickle charger of mine is approx 0.2 mA and through an old 6 amp charger approx 2mA)

The technical data for a good modern charger which is designed to be permanently connected should state the back current. Ctek quote <1 Ah per month for their M100 charger and <2Ah per month for the M 15 and M25 chargers.

I have never owned a caravan so do not know what "Carver panel" is or does and a bunch of Google searches have found nothing relating to the current topic.

 

[Refueler]

My thought is not so much the mA ... but the fact that its still passing something. It was only a comment anyway.

Carver Panel ? Many caravans have a control panel that switches the domestic supply of the caravan from car power when towing - to 12v or 240v on site.

Carver is a brand name .... there are of course many other brands ... I just know Carver from owning vans in the past.