Onboard charger output. | MotorhomeFun | The Motorhome Support and Social Network

Onboard charger output.

Mar 30, 2019
122
156
Funster No
59,476
MH
Coachbuilt
Exp
Since 2016
How can I determine the output of my onboard charger? . I do have a multimeter 🙂
 
Jun 8, 2012
1,345
1,140
Reading
Funster No
21,386
MH
Riot Van Conversion
Exp
Since 2012
The multimeter will tell you the volts on your charger output. However, that tells you only so much (although this might be enough depending on why you are asking). To tell amps, you will need some sort of shunt (an accurate low resistance device in line with the battery) to measure the voltage across that. Your multimeter might have such a 10A device built it, but it would be hairy to use it safely and it is one of those "if you need to ask" type questions.
 
Jan 19, 2014
4,913
12,403
Derbyshire
Funster No
29,757
MH
Elddis Accordo 105
Exp
since 2014
How can I determine the output of my onboard charger? . I do have a multimeter 🙂
Set the multimeter to volts DC and put the probes on the battery terminals. Sometimes the onboard charger is just a 13.8v power supply like our Elddis one was. To see what it's up to you've either got to watch it or get it's user manual.. Or Google it 👍

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OP
Itsmcb
Mar 30, 2019
122
156
Funster No
59,476
MH
Coachbuilt
Exp
Since 2016
The the make and model number and I'm sure one of us on here will find the info.
It's in a 96 Kontiki 640. Built into the power supply unit in the wardrobe. No labels at all sadly. Everything is working fine, I am thinking of adding a second 110 amp leisure battery and was just curious how quickly (or slowly) it might charge them.
 
Jul 6, 2009
164
201
Funster No
7,383
It’s 10 amp at 13.8 volts. It will really struggle to keep on top of 2 x 110 amp batteries. Depending on. How much demand. Rule of thumb min unit capable of charging at 10% of capacity

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Lenny HB

LIFE MEMBER
Oct 18, 2007
26,204
41,972
On the coast in West Sussex
Funster No
658
MH
Hymer B678 Dynamic Line
Exp
Since 2008 & many years tugging
It’s 10 amp at 13.8 volts. It will really struggle to keep on top of 2 x 110 amp batteries. Depending on. How much demand. Rule of thumb min unit capable of charging at 10% of capacity
If it is that type the Batteries will never get a full charge and will only last a couple of years. If you want your batteries to last you need to replace it with a decent multi stage cgarger.
 
OP
Itsmcb
Mar 30, 2019
122
156
Funster No
59,476
MH
Coachbuilt
Exp
Since 2016
It’s 10 amp at 13.8 volts. It will really struggle to keep on top of 2 x 110 amp batteries. Depending on. How much demand. Rule of thumb min unit capable of charging at 10% of capacity
I do have 270 watts of solar on the roof so during the summer I think the battery gets fully charged from that. I want to add a second battery to give more reserve through the winter. Can I add a second freestanding charger to use through the winter without disconnecting the existing one?
 

Lenny HB

LIFE MEMBER
Oct 18, 2007
26,204
41,972
On the coast in West Sussex
Funster No
658
MH
Hymer B678 Dynamic Line
Exp
Since 2008 & many years tugging
You would be better disconnecting the existing one as it is not doing your batteries any good.
If your current battery is much more than a year old you need to replace that as well when adding the second one.

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TheBig1

LIFE MEMBER
Nov 27, 2011
14,092
25,062
Dorset
Funster No
19,048
MH
A class
Exp
many many years! since I was a kid
if I recall correctly, there is a switch to turn the built in charger on/off. If you install an updated charger, remove the fuse for the built in one. Otherwise the new charger will see the constant 13.8v put out by the old one and assume the battery is fully charged
 
Jan 19, 2014
4,913
12,403
Derbyshire
Funster No
29,757
MH
Elddis Accordo 105
Exp
since 2014
I removed our old charger completely. It's left a nice slot in the top of the fuse box for the mini socket set and clamp meter 😎
 
Nov 21, 2020
21
37
Funster No
78,053
MH
Autotrail Imala 734
Exp
12 years
Im in a similar boat. I am thinking of remmoving the old 10a charger in the sergant control panel and addingt he Victron30 amp multistage somewhere.
My question is if I find the exisiting output cables from the old 10a would the cables from that to the batteries which I am (upgrading to lithium 200a) be ok to take the new current.

Thanks
John

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Last edited:

Lenny HB

LIFE MEMBER
Oct 18, 2007
26,204
41,972
On the coast in West Sussex
Funster No
658
MH
Hymer B678 Dynamic Line
Exp
Since 2008 & many years tugging
Im in a similar boat. I am thinking of remmoving the od 10a charger in the sergant control panel and addingt he Victron30 amp multistage somewhere.
My question is if I find the exisiting output cables from the old 10a would the cables from that to the batteries which I am (upgrading to lithium 200a) be ok to take the new current.

Thanks
John
Not in an Autotrail, cables are way under size for the existing install.
 

TheBig1

LIFE MEMBER
Nov 27, 2011
14,092
25,062
Dorset
Funster No
19,048
MH
A class
Exp
many many years! since I was a kid
just mount the new charger nearer the batteries and run an over specced cable between them

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OP
Itsmcb
Mar 30, 2019
122
156
Funster No
59,476
MH
Coachbuilt
Exp
Since 2016
if I recall correctly, there is a switch to turn the built in charger on/off. If you install an updated charger, remove the fuse for the built in one. Otherwise the new charger will see the constant 13.8v put out by the old one and assume the battery is fully charged
Ah, yes there is a switch on the top of the box👍. I can just turn it off, then I would have a back up if the new charger failed for any reason.
 
OP
Itsmcb
Mar 30, 2019
122
156
Funster No
59,476
MH
Coachbuilt
Exp
Since 2016
I have a single 230v socket in the locker near my battery (ies). Can anyone recommend a suitable charger ?
 
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