Insurance Quotes
Insurance Discount Campsite Offers All offers
UK Sites French Sites European Sites Map Search Text Search Near your Location Popular Searches Leave a Review My Saved Sites Add a New Site
All Sections Caravanning Camping Tent Talk Motorhomes Trailer Tents Backpacking Equipment Statics UK Campsites Camping Abroad General Chat News More Sections Latest Posts
All Adverts Tents for Sale Caravans for Sale Motorhomes for Sale Equipment for Sale Post an Advert Campsite Jobs
All Categories Caravanning Advice Caravan Equipment Tents and Camping Motorhomes Towing and Towcars Equipment Furniture and Cooking Electrical / Gas Shows and Events General More Categories
Join for Free Log In

Advertisement

Message Forums
Welcome Guest Register  Log In  Search  Latest Posts
 Reception - All Forums
  Motorhomes and Campervans 		Share   Post on X / Twitter  Share on Facebook  Email
Subject Topic: Charging engine battery
Post Reply
Personfleck2
27/11/2014 at 8:12am
 Location: Derbyshire
 Outfit: Elddis accordo Motor View fleck2's Profile View Profile   Reply to fleck2 Reply   Quote fleck2 Quote  
Joined: 27/4/2006

Platinum Member
Platinum Member

Forum Posts:   1188
Site Reviews Total: 8
Site Reviews 2026: 0 
Site Reviews 2025: 0 
Site Reviews 2024: 0 
Site Reviews 2023: 0 
Site Reviews 2022: 0 
Site Reviews 2021: 0 
Site Reviews 2020: 0 
Site Nights 2026: 0
Site Nights 2025: 0
Site Nights 2024: 0
Site Nights 2023: 0
Site Nights 2022: 0
Site Nights 2021: 0
Site Nights 2020: 0
I have a brilliant idea:

Has anybody fitted a diode between their leasure battery and engine battery so that when on hook up they both charge but the engine battery can't be discharged by the TV etc when not on hook up.

I'm thinking it would also need a current limiting resistor in series with it to protect the diode during engine cranking. Diodes have a small voltage drop across them but it's only about 0.5v.

Am I missing something? What do you all think?


Personfleck2
27/11/2014 at 1:33pm
 Location: Derbyshire
 Outfit: Elddis accordo Motor View fleck2's Profile View Profile   Reply to fleck2 Reply   Quote fleck2 Quote  
Joined: 27/4/2006

Platinum Member
Platinum Member

Forum Posts:   1188
Site Reviews Total: 8
Site Reviews 2026: 0 
Site Reviews 2025: 0 
Site Reviews 2024: 0 
Site Reviews 2023: 0 
Site Reviews 2022: 0 
Site Reviews 2021: 0 
Site Reviews 2020: 0 
Site Nights 2026: 0
Site Nights 2025: 0
Site Nights 2024: 0
Site Nights 2023: 0
Site Nights 2022: 0
Site Nights 2021: 0
Site Nights 2020: 0
Well I've connected it up roughly to measure what happens.

The engine battery was sitting at about 12.5v and leisure at 13.8v
If I connect them directly, the engine battery charges at 3.7a

After connecting the diode the engine battery starts charging at 1.1a but steadily falls. Last time I looked it was 0.7a

With the 10ohm resistor in line it only charges at about 50ma so the resistor is a bit too big.

With the EHU switched off the engine battery still takes a small charge from the pleasure battery, about 20ma. But that would drop to nothing after a while I think.

So far so good 😎


Personspartan3956
27/11/2014 at 3:10pm
 Location: staffs
 Outfit: Bentley Donington View spartan3956's Profile View Profile   Reply to spartan3956 Reply   Quote spartan3956 Quote  
Joined: 28/6/2012

Standard Member
Standard Member

Forum Posts:   84
Site Reviews Total: 0
Site Reviews 2026: 0 
Site Reviews 2025: 0 
Site Reviews 2024: 0 
Site Reviews 2023: 0 
Site Reviews 2022: 0 
Site Reviews 2021: 0 
Site Reviews 2020: 0 
Site Nights 2026: 0
Site Nights 2025: 0
Site Nights 2024: 0
Site Nights 2023: 0
Site Nights 2022: 0
Site Nights 2021: 0
Site Nights 2020: 0
Hi
I have a similar system using a solar panel connected to the leisure battery only
To top the engine battery i use a 12 volt charger from leisure to engine battery
it basically charges the engine battery when the leisure reaches 13.3 volts.
No problems when engine running
would work on electric hook up.

http://www.shop.sterling-power.com/acatalog/BM1.pdf


Personsaxo1
27/11/2014 at 4:26pm
 Location: None Entered
 Outfit: None Entered View saxo1's Profile View Profile   Reply to saxo1 Reply   Quote saxo1 Quote  
Joined: 29/10/2005

Diamond Member
Diamond Member

Forum Posts:   4490
Site Reviews Total: 0
Site Reviews 2026: 0 
Site Reviews 2025: 0 
Site Reviews 2024: 0 
Site Reviews 2023: 0 
Site Reviews 2022: 0 
Site Reviews 2021: 0 
Site Reviews 2020: 0 
Site Nights 2026: 0
Site Nights 2025: 0
Site Nights 2024: 0
Site Nights 2023: 0
Site Nights 2022: 0
Site Nights 2021: 0
Site Nights 2020: 0
On Hymer motorhomes when on hookup the vehicle battery is trickle charged and the habitation battery is charged via a 3 stage charger.
knarf


Personfleck2
27/11/2014 at 8:00pm
 Location: Derbyshire
 Outfit: Elddis accordo Motor View fleck2's Profile View Profile   Reply to fleck2 Reply   Quote fleck2 Quote  
Joined: 27/4/2006

Platinum Member
Platinum Member

Forum Posts:   1188
Site Reviews Total: 8
Site Reviews 2026: 0 
Site Reviews 2025: 0 
Site Reviews 2024: 0 
Site Reviews 2023: 0 
Site Reviews 2022: 0 
Site Reviews 2021: 0 
Site Reviews 2020: 0 
Site Nights 2026: 0
Site Nights 2025: 0
Site Nights 2024: 0
Site Nights 2023: 0
Site Nights 2022: 0
Site Nights 2021: 0
Site Nights 2020: 0
Quote: Originally posted by saxo1 on 27/11/2014
On Hymer motorhomes when on hookup the vehicle battery is trickle charged and the habitation battery is charged via a 3 stage charger.
knarf


My charger will be three stage but it doesn't charge the engine battery which seems a bit silly for the sake of a bit of wire and a couple of 50p components.
I suppose unless you're parked up for a month you don't need it to. We park up for longer periods abroad because you get a cheaper rate.

I've left it charging all afternoon and it's dropped down to a 270ma charge now, I'm going to have to test it with the engine running at some point, but I can't see there being a problem with it.

I tested it this afternoon with the EHU off and all the lights and inverter on inside and the engine battery showed no discharge at all


Advertisement

Wolfbox


Personwints
04/12/2014 at 10:08am
 Location: Leyland
 Outfit: Hymer S650 View wints's Profile View Profile   Reply to wints Reply   Quote wints Quote  
Joined: 06/2/2006

Standard Member
Standard Member

Forum Posts:   19
Site Reviews Total: 0
Site Reviews 2026: 0 
Site Reviews 2025: 0 
Site Reviews 2024: 0 
Site Reviews 2023: 0 
Site Reviews 2022: 0 
Site Reviews 2021: 0 
Site Reviews 2020: 0 
Site Nights 2026: 0
Site Nights 2025: 0
Site Nights 2024: 0
Site Nights 2023: 0
Site Nights 2022: 0
Site Nights 2021: 0
Site Nights 2020: 0
I've fitted this, it works a treat....it's a split charge device that will charge the engine battery, wether on ehu or solar, once the leisure battery reaches 13.6v.

Only 3 wires, easy to fit.

http://i.ebayimg.com/images/i/121413910665-0-0/s-l140.jpg

Allen


Personwints
04/12/2014 at 10:13am
 Location: Leyland
 Outfit: Hymer S650 View wints's Profile View Profile   Reply to wints Reply   Quote wints Quote  
Joined: 06/2/2006

Standard Member
Standard Member

Forum Posts:   19
Site Reviews Total: 0
Site Reviews 2026: 0 
Site Reviews 2025: 0 
Site Reviews 2024: 0 
Site Reviews 2023: 0 
Site Reviews 2022: 0 
Site Reviews 2021: 0 
Site Reviews 2020: 0 
Site Nights 2026: 0
Site Nights 2025: 0
Site Nights 2024: 0
Site Nights 2023: 0
Site Nights 2022: 0
Site Nights 2021: 0
Site Nights 2020: 0
Just realised the link is the image only.

The ebay seller is rpsleisure.

Hope that helps.

Allen


Personfleck2
04/12/2014 at 12:46pm
 Location: Derbyshire
 Outfit: Elddis accordo Motor View fleck2's Profile View Profile   Reply to fleck2 Reply   Quote fleck2 Quote  
Joined: 27/4/2006

Platinum Member
Platinum Member

Forum Posts:   1188
Site Reviews Total: 8
Site Reviews 2026: 0 
Site Reviews 2025: 0 
Site Reviews 2024: 0 
Site Reviews 2023: 0 
Site Reviews 2022: 0 
Site Reviews 2021: 0 
Site Reviews 2020: 0 
Site Nights 2026: 0
Site Nights 2025: 0
Site Nights 2024: 0
Site Nights 2023: 0
Site Nights 2022: 0
Site Nights 2021: 0
Site Nights 2020: 0
Yes mine has 3 wires ground and the 2 battery positives. I've put a little volt meter module in the circuit to see the engine battery voltage. It all fits in an old PIR light connector box so it's quite small. I've opted to have it free standing and the connection wires are on insulated croc clips.
Total cost is about 3 quid tee hee.
I can post pics and diagram if anybody's interested.


Personlisterdiesel
07/12/2014 at 9:38am
 Location: Rushden Northants
 Outfit: Mercedes 614D Conversion View listerdiesel's Profile View Profile   Reply to listerdiesel Reply   Quote listerdiesel Quote  
Joined: 03/7/2011

Platinum Member
Platinum Member

Forum Posts:   581
Site Reviews Total: 0
Site Reviews 2026: 0 
Site Reviews 2025: 0 
Site Reviews 2024: 0 
Site Reviews 2023: 0 
Site Reviews 2022: 0 
Site Reviews 2021: 0 
Site Reviews 2020: 0 
Site Nights 2026: 0
Site Nights 2025: 0
Site Nights 2024: 0
Site Nights 2023: 0
Site Nights 2022: 0
Site Nights 2021: 0
Site Nights 2020: 0
The forward voltage drop on a standard diode is about 0.6 - 0.7V, less if the diode is the Schottky type.

Obviously it will reduce the voltage from the leisure battery, but it will do the job required if the leisure battery is up on charge at 13.5V or so. Otherwise it won't do much at all.

Remember also that on starting the vehicle, the diode will try and pass a fairly large current as the starting battery volts fall sharply.

If the leisure electrics share a common negative with the vehicle electrics then a small DC-DC converter would do the job.

Peter



In order to post a reply you will need to register, or if already registered please log in here

Prev       Next
Quick Links - All Forums - Motorhomes and Campervans - Top of Page

     Share   Post on X / Twitter  Share on Facebook  Email


Latest News, Discounts and Competitions  see all...















    Upcoming Event

UKCS Meet Elvaston Steam Rally 2026 03/07 to 06/07

Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.


6659 Visitors online !

Free UKCampsite.co.uk Window Sticker  -  Add a Missing Campsite

[Message Forums]  [Caravan Sites & Camping]  [Company Listings]  [Features / Advice]  [Virtual Brochure]  [Special Offers]
[Reception]  [Competitions]  [Caravans & Motorhomes For Sale]  [Event Diary]  [Tent Reviews] 

[Contact Us] 



Please note we are not responsible for the content of external sites & any reviews represent the author's personal view only. Please report any error here. You may view our privacy and cookie policy and terms and conditions here. All copyrights & other intellectual property rights in the design and content of this web site are reserved to the UKCampsite.co.uk © 1999 - 2026


Advertisement
Advertisement

Advertisement