Hi AK,

I've got a transformer in my MH, I rewired it with a couple of relays to ensure it disconnects from the batteries when in use.  I did this because it cooked my batteries when we where in a shed for 3 months, when we replaced the motor 2 years ago. When we went into the shed the batteries were fully charged and we were running everything 12v off the transformer, problem was it was feeding a constant unregulated charge in to the batteries which in turn fried them.

Considering solar panels feed in to the solar controller at around 18 volts, I don't think the transformer could be used connected to the solar controller because it would only be outputting in the 12 volt range. Unless you can tweak the output to something that the solar controller is expecting to receive.  That said, if you have an MTTP controller it might work but I have my doubts, I would think a Battery Charger would be a better option.

Regards Steve.

-- Edited by madaboutled on Sunday 25th of February 2018 01:09:20 PM

Maybe something like this....

https://www.ebay.com.au/itm/Variable-Power-Supply-Switch-Mode-4-15V-60A-13-8V-12V-Ham-Radio-Car-motor-240V/263437746925?epid=625786113&hash=item3d561d02ed:g:maYAAOSwCkZZVKg3

Looking at the specs something a bit bigger that can be run continuously might be the go.

 

Steve.

Aus-Kiwi wrote:

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Is anyone using transformer to run 12v when batteries are low ?  It seems the chargers out there are not rated high enough or very expensive ??  I have 40 amp charger but supplies 18 to 22 amps on 300 AH battery pack . I assume its the regulator reducing charge ?  seems these regs are designed for single car batteries ? The solar charges them in morning by 10am on a nice day . Often wander if transformer connected to solar reg would do a better job ?? Or is it just the battery cycle and Im worrying, thinking of it too much ??  

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It is the battery "Impedance" that is limiting the charge

Battery "Impedance " [resistance to current flow]& is a combination of the batteries internal "Ohmic "resistance PLUS the actual battery voltage @ that point.in time. Any voltage drop in the battery charger  DC leads & connections can limit current flow

The charger sees that as part of the battery impedance

Check for voltage drop in DC  leads & connections while under load [charging]

The total should not exceed 0.25V, the lower the better!

You cannot / should not connect a "Transformer" to any solar panel or solar regulator or even to a battery[any DC source]

The solar panel & regulator will see that as a dead short [virtually no ohmic resistance]  the output of the transformer will be ZERO

Connect between reg and diode on solar . Mainly thinking at night or bad overcast days . One of two things to charge batteries quick to say ?? 12.6 volts or supply enough to supply feed. The trouble with MOST battery chargers is they drop the amps . The load is confusing the reg ?? Of course this is for short term charge . Not to be used full time !!

Aus-Kiwi wrote:

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Is anyone using transformer to run 12v when batteries are low ?  It seems the chargers out there are not rated high enough or very expensive ??  I have 40 amp charger but supplies 18 to 22 amps on 300 AH battery pack . I assume its the regulator reducing charge ?  seems these regs are designed for single car batteries ? The solar charges them in morning by 10am on a nice day . Often wander if transformer connected to solar reg would do a better job ?? Or is it just the battery cycle and Im worrying, thinking of it too much ??  

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The battery acceptance rate is what is causing the charge reduction because the regulator within the charger is trying to limit the charge voltage. If you force the charge voltage higher the current will increase, the battery will have the electrolyte boiling both from heat and electrolysis bubbles of hydrogen and oxygen and if it can't vent the gas the case will start to bulge. If it does vent the battery compartment is now so full of the perfect mix of gases to blow the thing to bits so you sure don't want a spark in there.

The end result will be a stuffed battery with buckled plates. Setting the charger to equalise mode will do just what you are trying to do and have the same results on all but flooded cell batteries.

 

If you don't want the battery internal resistance to cause the rise in charging voltage that is causing the charger to slow down, you need a better chemistry battery .... Maybe you are starting to understand one of the reasons people are changing to this better chemistry battery, this is the faster charging part, just one of the many benefits  

 

T1 Terry   

 

EDIT: By the way, you are not seeing fully charged from the solar by 10am, you are seeing the end of the battery acceptance of that charging rate and that is not even close to fully charged. If the charge rate is low then you might have reached 80% SOC, but generally more like 70% SOC and the remainder needs to be added at a much reduced charge rate, that is what you can see your mains charger doing. 

-- Edited by T1 Terry on Tuesday 27th of February 2018 04:20:46 PM

Aus-Kiwi wrote:

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I guess that could work as direct 12v supply ? Taking load off storage batteries. ? I have inverter / charger built into motorhome . It seems the 60amp charger section is not working. From memory a Mastervolt . The DC side doesnât get used much or more the point . Over 4 years I have hardly known the DC charger doesnt work .

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Hi Aus-Kiwi,

I had a Mastervolt unit in a previous MH. It was not charging correctly and I had it fixed. A really good bit of kit and worth the effort to fix it, 3 stage charging with temp compensation. The electronics tech was impressed with the quality of the older unit.  I believe the previous owner had connected the batteries back the front which is specifically warned against and it had blown a couple of items. It worked well then as a DC house supply and heavy duty charger and a seperate trickle to the truck batteries too. Better built than newer units you commonly find.

Jaahn     

Yes battery voltage is up over 13v by 10am ., what I am seeking to fix is the charging system at night even with charger on . It hardly charges batteries . The built in reg I guess is for a single 12v battery ? Where I have 3 X 120 AH batteries . The load which is sat box, TV . LED lights , maybe little 12v fan ? Another LED TV . . The charging is mainly an issue on overcast days . Yes I will get the Mastervolt fixed ! Yes it has temp sensor between batteries . Hope I explained this correct . At no point am I trying to charge without a regulator !! Was looking at transformer to imitate solar ., either through 240 or gene .. The Mastervolt i would guess has never worked ? Mainly because I have hooked up to 240 and batteries went low on overcast day.

Yes. Iâm just trying to prevent flat batteries or too much drain keeping the amber light on . At times it goes into red . From memory 12.5 v which I am trying to prevent go to . If I have 240 or able to start QUIET generator. Not so bad now we have fitted a low voltage sensitive cut out relay for motor batteries . Being diesel, auto .. Maybe I am looking into it too much or worrying over nothing !! No point trying to pioneer when there is a system there !! Just need to repair or replace it !