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Critique for my alt / battery idea please...


SiWhite
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Current setup on the 90 is two 90a Mondeo alternators wired through two charging circuits to two Optimas - one for vehicle electrics and t'other for the 8274.

I'm a bit wary of leaving the winch battery connected to the alternator for up to a month between uses - no real reason why, it just doesn't seem 'right' - I've been disconnecting the belt for the second alternator between off roading trips. I've experienced the belt slipping and melting before when getting heavy use from the winch, so need more juice for winching.

My plan is to keep the two alternators (I like thier non-price and the redundancy of two) but connect them via an X-Eng split charge relay to the two batterys as normal. I've a few questions.....

1. Will adding two alternators like this make 24v? Instinct says no, but I've previous for making mistakes like that before...

2. Does a battery mind being on charge for months on end without any use?

3. Would I get the benefit of both alts into the winch battery under heavy load?

Thanks in advance for the help as usual.....

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1. Will adding two alternators like this make 24v? Instinct says no, but I've previous for making mistakes like that before...

2. Does a battery mind being on charge for months on end without any use?

3. Would I get the benefit of both alts into the winch battery under heavy load?

1. No, still 12v.

2. A battery prefers to be charged, than not, regardless of use.

3. Yup, vehicle battery will be drained in winching too.

exact current draw depends on the subtleties of having matched batteries and alternators, though i don't know how relevant this would be in real-world use.

I take it you intend to use the split charge to seperate the batteries from each other?

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1. Will adding two alternators like this make 24v? Instinct says no, but I've previous for making mistakes like that before...

2. Does a battery mind being on charge for months on end without any use?

3. Would I get the benefit of both alts into the winch battery under heavy load?

Thanks in advance for the help as usual.....

1) As Luke says, same voltage add the currents.

2) Depends on the charger, it is possible to overcharge a battery but there are chargers that switch off and only come on again from time to time to maintain the charge.

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I take it you intend to use the split charge to seperate the batteries from each other?

Exactly, so I can drain the winch battery by leaving camping lights on (which will also come from the winch battery) and still start the engine.

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Current setup on the 90 is two 90a Mondeo alternators wired through two charging circuits to two Optimas - one for vehicle electrics and t'other for the 8274.

I'm a bit wary of leaving the winch battery connected to the alternator for up to a month between uses - no real reason why, it just doesn't seem 'right' - I've been disconnecting the belt for the second alternator between off roading trips. I've experienced the belt slipping and melting before when getting heavy use from the winch, so need more juice for winching.

My plan is to keep the two alternators (I like thier non-price and the redundancy of two) but connect them via an X-Eng split charge relay to the two batterys as normal. I've a few questions.....

1. Will adding two alternators like this make 24v? Instinct says no, but I've previous for making mistakes like that before...

2. Does a battery mind being on charge for months on end without any use?

3. Would I get the benefit of both alts into the winch battery under heavy load?

Thanks in advance for the help as usual.....

One way to do it would be:

1: Connect output (B+) from both alternators to common point - either on main battery positive terminal or common point on starter solenoid

2: Connect D+ (charge warning lamp) from each of the alternators over a charge warning lamp of minimun 2watt to independant (ignition switched) positive supply

Cables used in 1) and 2) should be of identical lengths and diametre - to ensure equal voltage drop and equal load sharing between the alternators. For 100amp generators 16mm2 cable would more than enough for the main feeds. For D+ circuts 1.5mm2 is ok. REMEMBER CORRECTLY RATED FUSES!

Then you would have a scenario where the load is shared equally between the two alternators.

If you choose so, the output from the two alternators can charge 1, 2 or more batteries. Connect the positive terminal on one battery to positive terminal on the other battery.

To make a split charge system the cheap and easy way using a small 30 amp automotive solenoid.

Terminal 86 on the solenoid shoud be connected to D+ on the alternator. This wire will only provide a small current to trigger the solenoid so can be made from 1.5mm2 cable and should be fused with a 5 amp fuse (as close to the alternator D+ as possible)

Terminal 85 on the solenoid should be connected to vehicle earth (1,5mm2 cable will do fine)

Terminal 30 on the solenoid should be connected to main battery positive terminal. 30 amp fuse as close as possible to the positive terminal on battery. Use 6mm2 cable.

Terminal 87 on the solenoid should be connected to the aux battery postive terminal. 30 amp fuse as close as possible to the positive terminal on battery. Use 6mm2 cable.

The two batteries should both have their negative terminal connected to vehicle earth.

(For winching the same principle regaring split charge systems can be applied, just use a normal winch solenoid rather than a normal 30 amp automotive solenoid)

Regarding your other question - a battery can be overcharged, but not by a automotive alternator, as they are fitted with a charge management system (by taking input current from D+ feeding a tiny amount into the field windings the output voltage of the alternator can be quite easily regulated. Your battery would very much rather stay connected to the alternator than not.

Hopyfully most of this will be understandable. I work with electronics every day, but we speak another language over here in Denmark! Any misleading gramatical blunders is purely uninteded!

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Be wary of using a winch solenoid for use in a HD split charge system, they don't like the continuous rating.

BTDT several times.

jw

There's a way round that with a bit clever relay circuitry - you arrange that once the solenoid has been called a resistance is connected in series with it, this reduces the holding current. This method is (was) used in relay logic circuitry to reduce power consumption and heat build-up. The contacts used to do this are known as "economy contacts."

I got round this problem on my fridge compressor project by wiring a bulb in series with a solenoid valve. The low cold resistance of the bulb allows sufficient current to call the solenoid, then the bulb heats up, its resistance increases and the current reduces but is sufficient to hold the solenoid.

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Be wary of using a winch solenoid for use in a HD split charge system, they don't like the continuous rating.

BTDT several times.

jw

Maybe you have been supplied the wrong solenoid...?

There actually are several different kind of Heavy-duty solenoids, some are biased towards short pulses of on-off, others are constructed for coutinous operation. This totally depends on the solenoid used.

Normal winch solenoids - as supplied with winches - are, at least from my expirience, pure carp!

Use the right hardware for the right job! Most solenoids the manufactures supply with winches is only rated for 80A continous. Letting the current flow throug the solenoid is actually the easy part for the solenoid - the tricky thing is wether the solenoid is able to switch (break) the current flow. Solenoids fails when switching a current, rarely by letting a current flow through (unless, of course, the solenoid is totally unaccpteble for the actual job)

Using the right kind of solenoids enables one to be 'creative' about split charging... A two (or four) battery system can be charged by two independent alternators (as per previous posting) then all connections to the batteries made through HD solenoids, then add another circut of HD solenoids from postive to negative - switch the first circut off, and the second circut on, then you have 24 volt for welding!

(And yes, if the solenoids are correctly rated, and of the proper type, they will have no problem coping with (or switching) the current flow.)

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I think the problem is with the coils overheating, not the contacts.

The pulling power of the solenoid coil depends on ampere-turns, so they tend to wallop as many amps through the coil as possible to get a strong mechanical action. They assume a winch solenoid will be intermittent in usage so they can get away with using thinner wire than they would with a continuously rated device.

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I think the problem is with the coils overheating, not the contacts.

The pulling power of the solenoid coil depends on ampere-turns, so they tend to wallop as many amps through the coil as possible to get a strong mechanical action. They assume a winch solenoid will be intermittent in usage so they can get away with using thinner wire than they would with a continuously rated device.

Didnt see your posting before posting my reply. Totally agree though (and you explained the facts much clearer and using much less words than I...)

Of the quality solenoids I have worked with, I have never seen one fail because of overheated coil, but again, it is a matter of choosing the right hardware for the job - or using clever solutions like you compressor setup!

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What you could try with a bit of ingenuity is to use a solenoid off a pre-engaged starter.

These have two coils, one to call the solenoid, the other to hold it.

The calling coil is earthed through the load, so after the contacts have closed it is effectively shorted out, contact being maintained by the holding coil which is earthed to battery neg. The hot ends of both coils are connected together and made live to call the solenoid.

EDIT

That said, it may be a bit more difficult in your split charge application as there is no load as such.

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