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I see all these adverts for £150 + split charging systems and I think to myself what's really in them and could I buy the bits and do it myself cheaper ?

Discuss

Mo :D

£20 quid forthis one, 20A max tho'

from the wiring diagram, unless someone can correct me, the split charging gubbins altertaly connects the alternator to one of two batteries - auto mode; some have manual mode that allows which battery to charge to be selected.

So I would hazzard a guess to say there is a small oscillator inside that swtich on/off one or two relays at most.

The expense would be to find high power relays; obviously this is limited by how much current the alternator can supply; 100 A would be ample.

If I were to make one, looking at maplin web site I would use 30A SPDT Auto 12Vdc or 20A SPDT Auto 24Vdc relay, cost £1.80 and make my owner oscillator timer using 555. I can't see why a car indicator relay, about £1 , can't be used to switch the relay, approx 3 times per second is fine - not the most efficient way as power will be lost due to having light bulbs to loadthe indicator unit.

I'd be interested to know the switching rate of split charge relays. You might want to keep the connection to the battery longer so maybe some toggle mechnism that is trigger when the indicator is used?

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Indeed you could.

Have a chat with SimonR or look at his website, X-Eng.

You couldn't get a nicer bloke, and his company has just started up so he needs some support!

Absolutely - but I don't understand this on Simon's website

Additionally, when the winch is running and the alternator is charging, power will be drawn from both batteries (through the split charge). This current could be as high as 200A which is even more likely to toast your split charge!

Is this really true ? Whats the point of having a split charge if the power is being drawn through both batteries.

Also where does 200A come from, some winches are pulling more like double that now-a-days.

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Indeed you could.

Have a chat with SimonR or look at his website, X-Eng.

You couldn't get a nicer bloke, and his company has just started up so he needs some support!

oop!! maybe I shouldn;t have posted my stuff on making a split charge on the cheap!! :unsure:

re: Additionally, when the winch is running and the alternator is charging, power will be drawn from both batteries (through the split charge).

hmmmmm; I cannot see how that can happen; the one wiring diagrma I have seen is that split charge is connected between alternator and batteries; and the wires from battery go to the winch; no current should flow from battery to the alternator via the split charge relay. :(

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The reason for having a split charge is that most batteries will be damaged by connecting them permanently in parallel (Eh Nick!). The reason for this is that if one has slightly more charge than the other - it pushes current into the other, but overshoots a bit. The other one pushes the over-shoot back, and it over-shoots a bit and so on. The charge is cycled between the batteries and each time, a little is lost as heat.

Over time this can flatten the batteries - which they dont like!

There are two common ways of making a split charge.

first is using a pair of diodes. I diode is just like a one way valve - it allows current to flow in one direction, but not in the other, but just like a one way valve, there is a pressure drop across it - which manifests itself as a voltage drop of 0.7v (or so)

This system allows the alternator to push current into two batteries, but does not allow any to flow between the batteries. This means that your winch will only draw power out of one battery. This is fine, except for the 0.7v loss - which means your batteries will not fully charge.

You can achieve the same thing with MOSFETS with a much lower voltage drop - but these type of split charges are much more expensive.

The simplest solution is essentially a relay which connects the two batteries together in parallel - but only when they are being charged or discharged (which is fine).

The rest of the time the batteries are disconnected.

In this instance, if your winch is drawing 400A, half will be drawn from each battery. (That's where the 200A comes from).

When my 8274 is stalled, it draws 175A from the other battery (according to my clamp meter) - therefore the split charge needs to be able to handle at least 175A.

If the relay which connects the two batteries together is only rated at 20A - it will quickly toast itself!

The 20A split charges are fine for caravans where you will likely only be running a fridge - but not for winching!

A common solution is to use a winch type solenoid as the relay. The problem is that the coil is not continuously rated and they tend to fail fairly quickly.

Mine has a continuously rated coil and contacts continuously rated at 180A. I have tried pushing over 1000A through it for a short duration and it still works (shorting an Optima out with it!). Even if you are drawing well over 180A through the relay, your winch motor will burn out before the relay.

The main thing I'm offering is easy to understand instructions on how to set it up and how to wire up your winch to get the best out of it. Most of the people who have asked for advice on why their winch cannot pull the skin off a rice pudding have made simple mistakes in the wiring and it was my aim to give both that and a decent high current split charge as cheaply as possible.

If electrickery is your thing - then you will be able to do it more cheaply - but if not, I think this represents far better value than most on the market!

What extra do you get in a £100 split charge? Mostly you get a nice anodised aluminium heat sink and some blue LED's.

Si

PS Cheers for the +ve comments!

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O2, the last thing you want from your split charge system is toggling between batteries. This would give the same effect as constantly attching and removing the jump leads after starting someone else's motor and we all know that that process leads to dead alternator regulators don't we?

There are split charge systems that will connect or disconnect a battery while charging but if done properly through a "soft start " mechanism no harm occurs. These systems use logic to control their operations and are thus more expensive.

jw

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Further, if the engine is running and the split charge system has connected both engine and winching batteries the load applied by the winch to its battery is transferred to the engine battery AND the alternator. For a short period this is acceptable, however, for a long winching job the alternator is being taken outside of its normal operating parameters and will generate excessive temperature. Even worse , if the alternator is of the externally excited kind it no longer has the protection of the normal self limiting design and can self destruct.

jw

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Further, if the engine is running and the split charge system has connected both engine and winching batteries the load applied by the winch to its battery is transferred to the engine battery AND the alternator. For a short period this is acceptable, however, for a long winching job the alternator is being taken outside of its normal operating parameters and will generate excessive temperature. Even worse , if the alternator is of the externally excited kind it no longer has the protection of the normal self limiting design and can self destruct.

jw

Thanks Col - server re-started.

JW, if this were the case, your alternator would probably catch fire if you were to bump start a car with a flat battery - it having to deliver it's full rated load for best part of an hour?

I agree that alternators are not continuously rated, but the duty cycle of an alternator vastly exceeds that of a winch motor. Your winch motor will catch fire long before the alternator is worried!

There are 'proper' managed split charge units about - however, the alternator, batteries and everything else in a Land Rover are abused on a normal basis to an extent that a gentle, electronic managed charger is highly unlikely to have any bearing on the time between failures. Such a feat of electronic wizardry - to my mind is more of a liability in the kind of conditions we operate in. Give me something I can fix with a hammer any day!

I can see this will probably degrade into one of those conversations about how your HiFi sounds so much better because you re-mortgaged the house to buy gold speaker wires.

If you've spent £140+ on a split charge - and it works for you - that's brilliant. I just don't believe the extra cost is justified.

Si

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Pushed the send button before it had finished booting!

Today, it was the database back-end which went down - and refused to come back up! Time to dump MySQL and 'upgrade' to SQL Server me thinks!

Thanks for keeping me posted!

Si

Off to the pub now! (Sorry to keep you waiting Chris!)

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So if I've got this right, you've got a number of options

1) Mosfet split charge - flawed because of the voltage drop

2) Simonr split charge - discharges the batteries together and could leave you stranded

3) Parellel connection - can damage batteries unless perfectly matched and can flatten both batteries

4) Spendy battery control system

All of those are flawed for what I want, which is a fully charged starter battery - even after a long winching session.

So I'm thinking of a manual system

60510.jpg

One of these rated at 175A, about £25. Just to switch the alternator feed to whichever battery I want charged.

I guess with well matched batteries I can leave it on both, unless heavy winching or starting, in which case I just switch to battery one or two.

Switching to off will probably blow the alternator :( But maybe the switch can be pinned to prevent the off position being selected.

Dual voltmeters or some kind of changeover switch would complete the system

Discuss :D

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Almost!

It's the diode type that have a voltage drop.

The MOSFET ones are Spendy.

The SimonR ones, could leave you stranded - but they (or very similar) are what most people use.

The change-over switch is not a bad idea - it's just remembering to switch it back to charging the main battery once you are done - which is also likely to leave you stranded.

A last option (just to confuse matters!) is to use what is called a voltage sensitive switch in conjunction with a simonr type setup.

These are fitted to Defenders in line with the rear de-mist. If your battery is below about 11v, it will not switch on the de-mist.

If you connect one of these to the terminals of the main battery and connect the contacts in series with my relay, if the main battery gets too discharged, the split charge disconnects so the winch is running only off the second battery. The alternator charges the main battery until it is > 11v and then resumes charging both. I would incorporate one of these, but the VSS is about £30. Or 50p from Sodbury!

This makes it absolutly fail-safe.

In practice, I have never managed to completly discharge both batteries while winching. Assuming you leave the winch motor to cool down for a reasonable time, the capacity of both batteries will pretty much be restored.

I'm only running a 70A alternator and using two yellow top Optima batteries with a 4.7kw winch motor. This would give about 15 mins continuous winching time at full load. The winch motor would be toast after less than 5.

In practice, the time at full load (almost stalled = 430A) rarely exceeds a minute - and if it does, you should be using a snatch-block. This will reduce the winch current (on mine) to about 200A - giving about 30min run time with the alternator charging.

I feel pretty safe on the being stranded front.

Try the big switch - it's not a bad idea - I'd just worry about my goldfish like memory ;-)

Si

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Voltage Sensitive Relays are definitely the bomb proof option and are not that expensive [and transferable, so you can get a long life from your investment]. They are compact and have few drawbacks. Rather like older split charge relays (which close when the ignition is switched on), VSR's are activated by their own internal Battery Monitoring System.

Best option is to purchase a marine grade VSR as they are rated for permanent exposure to moisture. Merlin Equipment supply good value and well made kit.

VSR's stay open (off) when the engine is charging. Once the engine battery has reached 13.7V from the alternator charge, the relay will close allowing both engine and domestic battery banks to be charged.

When the engine is stopped, the voltage returns to normal levels allowing the relay to open again - separating the engine and domestic batteries. Unlike diodes, VSR's have ZERO voltage drop (so require no battery sensing on alternator or charging device) and won't allow overcharging.

Merlin's larger 200 amp model is fitted with an Emergency Parallel feature. By pressing a button on the instrument panel, the VSR will hold both the engine and domestic battery bank in parallel for ten minutes. This will allow starting of the engine from the domestic battery bank. Once this time has passed, and the voltage is up high enough (13.8V), the unit will stay engaged until voltage falls back to normal levels.

VSR's are mono-directional - i. e. they sense off one battery only (usually the engine battery and allowing charge to the domestics). Therefore, if you have other charging sources (e.g. solar panels) which are required to charge the engine battery, a 2nd VSR is required (sensing off the domestics and allowing charge to the engine battery).

Size the VSR for the largest charging source on board - e.g. a 100A alternator, use a 130A VSR.

Neil

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A last option (just to confuse matters!) is to use what is called a voltage sensitive switch in conjunction with a simonr type setup.

These are fitted to Defenders in line with the rear de-mist. If your battery is below about 11v, it will not switch on the de-mist.

Si

Thanks for taking the time with this - a really interesting thread,

Stranded through winching I'm not worried about. Its stalling a wet V8 in Moglite and not having a full battery to crank it over is my concern.

Does anyone know if those switches are in a Range Rover (c1991) as I have a loom for that spread all over my garage !!

Andy

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Andy,

Look for a yellow box a little bigger than a regular relay (about the same size as a flasher) with VSS written on it.

In a defender, it lives inside the dash, not in the normal relay panel.

May not be yellow in all cases.

If it has rear de-mist, it probably has one!

Si

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