80 series second battery for leisure, retaining 24 volt start..?

[Lorin]

I was just wondering.......

What would be the problem(s), if any, of using the second battery on an 80 as the leisure battery? Aside from the obvious that if it was drained, the truck won't start!

If I understand correctly, the second battery only comes into play when starting the truck. At all other times it is isolated from the truck electrics other than the alternator for charging (if this is not so, it can clearly be done as per the 12 volt start conversions). If so, what if all the leisure electrics were to run off it through a voltage disconnect that ensured enough power was always retained to start the truck? Add in a solar panel (which I intend to) to assist in keeping the battery topped up and it is unlikely the disconnect would ever have to kick in.

I also think think it is possible to fit two smaller 75ah batteries into the battery tray, giving a reasonable capacity for leisure. If they were wired in parallel am I right in thinking this would still be fine for the 24 volt start?

Why am I asking? Because if it would work, it would save me the cost/hassle of converting to 12 volt start just to get the leisure batteries under the bonnet, which is where I want them.

 

[Pumpy]

Why? do you really need that awkward space next to the wheelarch where the leisure battery normally goes for something else?

Advatages: it's under the bonnet where you want it, spare space next the wheelarch.

Disadvantages: Longer heavy cable run through bulkhead to aux fusebox; extra circuitry to prevent excessive drawdown on starter battery, possible diminished starting umph on a cold high altitude morning in the middle of nowhere; can't use a cheaper big 110Ah...

Sorry it's not the techy reply you're after, but worth a rethink?

 

[stumog]

Where is the space near the wheel arch you talk about pumpy? Can you post a pic of the location of yours?

 

[Pumpy]

mines in there, in the dark...

 

[Lorin]

Unfortunately that space is allocated! I also want all my electrics under the bonnet ideally.

 

[stumog]

I did think youeant there.

 

[stumog]

I thought that the nearside battery go a shot of 24v at starting. Something like that which means you can't use it to feed anything.

I don't have any feeds that come off it.

My battery is behind the back seat. And will be putting it back there once I build the storage in the back

 

[Lorin]

Yeh you likely have a point there Stu. But wouldn't both batteries get the 24v spike when starting?

 

[StarCruiser]

There is no 24v 'spike'. There is nothing but 12v across each battery. They are across each other, + to + and -to - during non start periods when the alternator charges them both 'in parallel'. When it comes to starting, the relay clicks in and disconnects the + to + and -to - connection s and links the + of the right hand battery to the - of the left. The - of the right hand battery remains solidly connected to the chassis, engine and body and the + of the left hand remains solidly connected to the starter terminal.

Your idea is worthy of thought, and I will give it some (when I remember). Potential problems I foresee are:-

1, The need to have really good (conduit) insulation and protection for the conductors on the leisure (left) battery and the knowledge and understanding (warning) that 24v will exist at times from + to chassis earth.

2, the need to look into battery compatibility for both starting and leisure use. Leisure batteries are usually capable of lower currents but a deeper discharge whereas starter batteries give high current for short bursts and do not like to be deeply discharged. That said, I believe there are batteries that can accommodate both.

3, any charger would need to be compatible with being bridged out, or careful thought would need to be given to where the connections were made/ taken from.

4, you would need to run any leisure wiring as a + and - pair. Absolutely no chassis earth return could be used…ever!

Those are my first thoughts but they dont blow it to pieces for me. This could be an interesting one.

 

[Towpack]

The only issue you may have is the 'unbalanced' charging the batts will suffer if the LHS battery is heavily discharged when used as a leisure power source, leaving the RH batt with an (almost) full charge.
You wouldn't get 24v across the + and - of the LH batt alone during starting provided you use seperate + and - cables directly from the batt posts and not the vehicle chassis/body earth, to the leisure equip you want to power.
2 x 75ah batts wired in parallel and fitted in the RH tray could effectively be treated as one batt. JMO

 

[Chris]

I've been through all this and I'm glad that there's two respected voices answered the question already. All that technical stuff if good, but here's something from my experience having split the two. I did the split and added an Optima yellow under the bonnet as a leisure battery. I also added a yellow in the back charged from a CTEK DS250 and Smartpass. The battery in the front just got connected through a Nat Luna split charge relay. This isn't a split charger it's just a splitter. Whilst the battery in the back was very happy and continues to be so around 2 years on, the front Yellow suffered quite quickly. Performance dropped off and unless I connected it to my mains CTEK charger, it just wouldn't come up to the right capacity. The alternator just isn't enough to properly service an Optima AGM battery. People who say Optimas aren't any good have most likely been trying to charge them as a normal battery. I swapped it out recently and put a standard cranking battery back in and that's as happy as anything. It has a much bigger Ah capacity than the Optima (which work in a different way) so using it as the leisure battery doesn't knock it too hard and it charges happily from the car's alternator. The Optima I took out is still fine and been on charge today sitting at nearly 15v. A car alternator only runs at 14.5 volts until the cranking battery is full, which generally takes very little time given how well Cruisers start. If you've had all your gear running in camp all evening, you won't replace the charge taken by just driving along.

So, however you split it, be aware that battery choice is important. I am not sure that splitting their roles and keeping 24v start is the right idea for battery life. Better to go 12v start put a quality battery in the second slot and connect with a smart charger.

 

[Lorin]

Chris, I agree with you re the charging for the leisure battery. If this idea was possible I'd want to also disconnect the parallel connection between the two sides and charge the leisure side via a smart charger - a Sterling b2b in my case. I'd also be using standard lead acid batteries.

My question was really just to see if there was a way to avoid the expense of having to do the 12 volt start conversion. I have thought that if it really was 'easy', surely it would have been done, but I am curious to know what the barriers are. If it is possible, I would look at doing it. If my starter then ever failed, fitting a 12 volt and doing what's needs doing to the start relay would then make absolute sense.

 

[Temujin]

mines in there, in the dark...
View attachment 103631

Hi, I'm in the process of fitting a leisure battery to my 80 4.2Td - Please can you give me brief details of your wiring system - ie did you connect your leisure battery to one or both of the front batteries of the your 80. Thanks

 

[Chris]

This is a 4 year old thread. Got to be a record surely! Hi Temujin. There are several ways of doing this and really you need to perhaps give a little more detail beofre we can narrow it down a bit. What sort of battery, where, what sort of useage etc etc.
But in principle, you'd connect to the UK passenger side battery to get a feed. But personally, I wouldn't go directly to the 3rd battery. I'd suggest some kind of split charge device at the VERY least between the two plus fuses of course. Better than that, I'd fit a DC to DC charger in there.

 

[Temujin]

Hi Chris, Thanks for your reply!
Yes, I am planning to have a split charge system - I'm going for a good quality AGM leisure battery - to run a fridge, a few lights and an inverter.
I thought about putting a DC to DC charge in the setup - my only question is that - do these only work with 'intelligent' alternators?
Any information on setup/equipment to use will greatly appreciated.

Thanks again,

Temujin

 

[Chris]

Noooo, the DC2DC unit eliminates any issues with input current. You can feed it from a wind turbine if you like or a hamster in a wheel. It ensures the best output to the battery from whatever you stick in it. IF you use an AGM, I would say it's essential to use a DC2DC unit. Without going over other threads on the matter, experience has shown pretty much overwhelmingly that feeding several batteries directly with one alternator isn't good. The alternator only sees one massive battery and can't possibly work out which each one needs. It's bad enough having two factory batteries under the bonnet without adding a totally different one in the back.

Alternators give out 14.5v until they sense fully charged then drop back to 13.8v. This isn't just intelligent ones, they all do it. So if the vehicle drops back to 13.8v and your leisure battery isn't properly full, it will only get 13.8v minus the drop over the cable of course. And that's simply not enough for most AGM batteries.

In a nutshell really.

 

[Temujin]

Hi Chris,

Thank you so much for your reply, your advice has been invaluable!
I am currently planning to turn my truck into an overland camper - so no doubt I'll be asking for your advice again!

Thanks again.

Very kind regards,

Temujin

 

[Chris]

It's why we're all here. We all started somewhere.

 

[Temujin]

Cheers mate!