Instructables

Fitting a leisure battery to a Mazda Bongo

If you want to use your Bongo as a camper van then it's a good idea to fit a second battery to run your interior lights, radio and camping junk from. Using a simple split charging system you can insure that you don't run you main starter battery down whilst being able to charge your leisure battery whilst on the go.

If you're fairly competent then the the job should take about 2 hours to complete.

If you're interested in Mazda Bongos check out the U.K. owners club here Bongo Fury
 
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Step 1: What exactly are we doing here

First things first. We need to clarify exactly what we are trying to achieve.

I am not going to describe how to wire up your goodies or how to rewire the internal lights etc to run from the leisure battery (that's another howto). I am going to explain how to wire up a split charging circuit so that your leisure battery gets charged up as you drive along.

Your starter battery is connected to the alternator of the van so when you drive along it gets charged. If we connect our leisure battery in parallel to the starter battery it will also get charged as we drive along.

Unfortunately it's not quite that simple. There are a couple instances when we don't want the two batteries connected.

1) Since the starter battery is the most important battery we need to insure that it gets fully charged before we even think about charging the leisure battery.

2) If we are stationary and using the onboard electrics we don't want to risk a flat starter battery so we must ensure it's disconnected from the leisure battery.

To do this we use a special relay that connects / disconnects the two batteries according to the above criteria.

The special relay is a variously called a voltage sensing relay (VSR), smart relay, battery isolator and several other names I can't remember.

It works by only making its switched connection when the input volatge reaches a preset level and unmaking its switched connection below that preset level.

To make sure we only charge the leisure battery when the engine is running and the starter battery is fully charged we need the VSR to make at about 14 volts. When the engine is not running or the starter battery is not fully charged the VSR will see less than 14v and so won't make. This matches the criteria set out earlier.

So our simple parallel circuit now has a smart switch added.
Hycro3 years ago
Would the leisure battery be a deep-cycle battery? If not, wouldn't a deep-cycle battery be better for running accessories for long periods of time??
Kevanf1 Hycro3 years ago
There are three sorts of automotive battery. Standard starter batteries that need constantly topping up (trickled if you like) to stay in top condition. Then at the other end are deep cycle batteries that can be discharged near enough fully without being harmed. In between these are the so called leisure batteries. These can be used as a sort of heavy duty starter battery or a lighter duty 'caravan' battery.

That's a very condensed way of putting it but, in essence, to answer your question, yes, a true deep cycle battery is best but a leisure battery is fine and a fair bit cheaper.

If you are interested the difference is in the way the battery is made. Deep cycle batteries have much more heavy duty plates and some are chemically different (as well as there being specialist gel batteries).
Kevanf13 years ago
Thank you for such a detailed but easy to follow 'ible'. I have an old Land Rover that I intend adding a leisure battery to (only for internal lighting and possibly fridge though, not a winch). I've been looking at various split charge systems and they are pretty pricey for Land Rovers yet are near enough the same thing as this.

Well done.

Take care.

Kevan
 great instructable, but it was a way easier way of doing that. If you get a distribution block, you could splice the positive wire from the alternator and run it to the second battery and put a 12v battery isolator in line with the positive wire. then just ground the battery. 

the isolator is $20 USD on ebay and the distribution block is around $7 - $20 USD (anything over $20 USD is over priced!) on ebay.
Sponge7 years ago
Thanks very much for writing this! Followed, installed and working perfectly last week! (Modified by using water resistant 30A blade fuse holders instead. Availabe from Maplins.)
voxx_man7 years ago
Knowing that there are people out there writing these kind of instructions make buying my Bongo 10 times more enjoyable, thanks loads, I'm going to attempt this at the weekend. I look forward to see other stuff soon, cheers again
jonbongo7 years ago
Looks great. I have a question, I have a leisure battery already in my Bongo for fridge and electric water pump. It worked fine and then intermittently and now doesnt seem to work at all. I've charged the battery 100% but this hasn't changed anything. do you have any ideas where the problem may lie? Thanks.
Every time you use a lead-acid battery, you damage it. The amount of damage is related to the depth of the discharge. If you discharge it only a little, to 90%, you can get thousands of cycles and years of service. 50% is considered a reasonable tradeoff between battery preservation and reasonable use. Thus, you should buy a battery with roughly twice the capacity you actually need. If you discharge it flat, it will damage the plates badly, and you will only get about 10-20 cycles before it is toast. All the charging in the world will not fill it. This is probably what happened to yours, if it was running a fridge - they can suck batteries down dead really fast.
rigglet7 years ago
Great instructable. Interested to know, are you going to create another for the next stage of the wiring? As a newbie to van conversion I was really encouraged by your instructable, and I'm trying to soak up as much info as I can. A site like this is invaluable. Cheers.
pringle7 years ago
Very nice instructable! only if i saw this sooner! Hope you can post any of the other bongo related stuff P.S we just purchased a mazda bongo and are part of the bongo fury club
corblimey (author)  pringle7 years ago
Hi Pringle Glad you liked it. I do intend to put more stuff on as I go. I actually find writing these generally more time consuming than doing the actual job. It is satisfying to think you've helped others though. I'm sure we'll bump into each other on the forum if you lurk there too. Cheers Corblimey
LasVegas7 years ago
Looks good, but how does the leisure battery charge? As it is, it looks like the leisure battery will eventually discharge. I suggest perhaps adding a large diode at the relay with the anode at the Starter battery's positive lead and the cathode to the Leisure battery's positive lead. This would pass the charge, if needed, to the Leisure battery.
corblimey (author)  LasVegas7 years ago
It charges from the alternator via the starter battery in parallel. The batteries are only connected when there is sufficent power to charge the leisure battery i.e. when the engine is running and the starter battery is fully charged. Under those conditions there is nowhere for the battery to dischagre to (apart from the connected lights, etc.) Your suggestion of a diode is actually common practise and they are in fact called split charge diodes. They are commonly used in marine applications but suffer voltage drop across the diode and are not generally favoured in automotive applications. They also require rewiring of the alternator feed to the batteries which is not such an easy job (from a practical point of view), There are newer versions of these "diodes" using mosfets that don't suffer the ineffeciency but they still require the heay duty rewiring.
Okay... So the relay switches in the Leisure battery rather than switching between them. So, if the Leisure battery is only switched in during charging, is it also connected to supply power to something (IE: An Inverter?) when it's not switched in? Otherwise, I don't understand its benefit.
corblimey (author)  LasVegas7 years ago
Yeah, you got it. It is a little confusing as to the leisure battery's purpose becasue I haven't actually connected anything to it yet! I will be wiring up my van's internal lighting, stereo and other 12v accessories to it but haven't progressed that far yet.
That's the idea :) You can hook up a power distribution block behind (same side as second battery) the relay/isolator and ground to the chassis :)
HamO7 years ago
Very well done! I like it. Great pix, nice instructable. Thanks for sharing.