Keeping a secondary battery topped up from the primary?

cormie

I had a hugely overwhelming and complicated thread here before about using a secondary battery to power dash cams where the secondary battery would only be charged when the van is running and the dash cam would feed off the secondary battery when the engine was off, so it would never drain the primary, but that even if the secondary was drained and the dash cam had turned off due to lack of power, it would instantly turn on as soon as the ignition comes on.

It got very complicated, so much so that I never ended up achieving what I set out, but I think part of the problem was the batteries I had for it, weren't on par with the primary battery.

Anyway, now I'm hoping this request is a little easier. I'm just looking for advice on how I can keep a secondary battery, that's pretty much identical to the primary battery, topped up when the ignition is on? This battery's primary use will be to have as a spare battery in the case a van needs a jump start, to either connect jump cables to it, or take out the flat and put this one in.

Any advice that a complete ignoramus when it comes to electronics/voltages/ampage etc could understand would be great

Cee-Jay-Cee

Solar charger would be the simplest and cheapest method.

Solar Trickle Charger

I use one to keep the battery in my ride on mower topped up over winter when its not in use. Works a treat.

TrailerBob

Long range 4x4 guys use a split charge unit and a second battery or sometimes 3 with one as a full leisure battery. Check out the cTek units, but they can be pricey

Joe 90

Something like this ?

Cheapest option is a split charge relay. Typically camper van has one fitted. It's basically a high amp rated relay (mine is rated at 70 A) connecting the extra battery to the main battery when the alternator light goes out. Most alternators have a dedicated terminal that is energised only when the alternator kicks in which will be perfect for this purpose.

gctest50

This kind of thing :


http://www.ebay.ie/itm/201653671385?rmvSB=true




when the engine is running, it connects the two together

when the engine is stopped, it disconnects them

colm_mcm

Split charger and leisure battery?

mikeecho

cormie wrote: »

Any advice that a complete ignoramus when it comes to electronics/voltages/ampage etc could understand would be great

Find an auto Electrician , let them do the work

cormie

Thanks a lot for all the replies. I want this to be a simple enough set up that I wouldn't need an auto electrician if possible. I definitely like the idea of a solar trickle charger that I could just keep on the dash and simply unclamp from the battery when I need it, they all seem to only have 4 stars on amazon though so I'm hoping there's one decent enough to keep this battery charged:
https://www.tayna.co.uk/Type-110-Varta-Silver-Dynamic-F18-585-200-080-P7709.html

?

Isambard

my camper had a leisure battery but when this packed up, I replaced it with a standard battery because it was cheaper and I barely had a need for a leisure battery. Paid dividends on top of Exmoor when I flattened the main battery by leaving the lights on all night.....just jumped start one from the other.

cormie

I didn't realise there's a difference between a leisure battery and standard batteries? What's the difference? I thought a leisure battery was just a standard battery referred to as a leisure battery to signify it's not necessary to start the vehicle and is just used for power for the fridge or whatever

Isambard

You can't use a leisure battery to start the vehicle apparently...it will kill it ....too many amps or something

coylemj

OP, the system you're looking for is pretty standard on cabin cruisers as well a camper vans so if you're anywhere near a marine supplier you could talk to them. Last time I recall it being discussed, the gadget that switches the charge to the secondary battery when the primary is full is called a 'diode splitter'.

mgbgt1978

http://www.12voltplanet.co.uk/split-charging.html

Op, have a look at the above. The VSR is probably your best bet, and your secondary Battery can be quite small (a small Moped Battery, etc.)

grogi

cormie wrote: »

I had a hugely overwhelming and complicated thread here before about using a secondary battery to power dash cams where the secondary battery would only be charged when the van is running and the dash cam would feed off the secondary battery when the engine was off, so it would never drain the primary, but that even if the secondary was drained and the dash cam had turned off due to lack of power, it would instantly turn on as soon as the ignition comes on.

It got very complicated, so much so that I never ended up achieving what I set out, but I think part of the problem was the batteries I had for it, weren't on par with the primary battery.

Anyway, now I'm hoping this request is a little easier. I'm just looking for advice on how I can keep a secondary battery, that's pretty much identical to the primary battery, topped up when the ignition is on? This battery's primary use will be to have as a spare battery in the case a van needs a jump start, to either connect jump cables to it, or take out the flat and put this one in.

Any advice that a complete ignoramus when it comes to electronics/voltages/ampage etc could understand would be great

Connect two in paraller and put a simple relay switch before the aux one that will disengage when no voltage on Accesory line is present.

gctest50

grogi wrote: »

Connect two in paraller and put a simple relay switch before the aux one that will disengage when no voltage on Accesory line is present.

The "intelligent" relays won't connect them together until the alternator starts charging

Saves power being drawn from the aux. battery during starting

grogi

gctest50 wrote: »

The "intelligent" relays won't connect them together until the alternator starts charging

Saves power being drawn from the aux. battery during starting

From the top of my head, a 13V zener would provide enough of intelligence for the relay