Are split charge diodes just for alternators? I want to split my solar charge.

[Baloo]

Hi All.

 

I am about to split my battery bank of six 110ah batts into a bank of two and four.

I'm going to be using a '1, 2, Both' selector switch and intend to select 'both' only whist running engine.

 

I have 240w of solar on the roof of the boat being controlled by a 20A Juta mppt.

I have a further 160w and wind gennie being controlled by a marlec controller.

 

I was planning to take the feed from the Juta and Marlec controllers to a split charge diode and then on to the two separate banks. I have just bought a sterling 70 amp split charge diode, but reading the instructions and wiring diagram that came with it I think I have realised that if I connect it up as I was planning then the controllers will 'think' that they are not connected to any batteries.

 

Do I need a different piece of kit, or is what I'm attempting not possible?

 

Any help gratefully received.

[Tony Brooks]

No, but a straight forward split charge diode is very bad news re efficient battery charging.

 

Personally I would correctly wire both charging systems and the use a heavy duty voltage sensitive relay to do the charge splitting. This will have close to zero voltdrop and will react to voltage rise so it will split both the alternator and solar charge. An ordinary split charge diose will create up to about 0.7 V of voltdrop.

 

By correctly wired I mean that both the solar and the alternator feed the domestic bank and the relay is used to charge the engine battery. I have explained in other threads why this is a good idea.

 

You can get so called zero voltdrop split charge "diodes" but they are electronic and more expensive.

[bottle]

Why?

 

Every time this has come up (two banks and assuming domestic bank) it has not been advised.

 

Peukert is the word that appears.http://www.smartgauge.co.uk/peukert3.html

 

Also 'split charge diodes' are not advised as they cause a volt drop, usually a 'split charge relay' is advised

[Tony Brooks]

I agree with Bottle - why?

 

You may have a very good reason but its not usually a good idea. Often when this sort of idea comes up its to "cure" and underlying fault and its usually better to solve the fault rather than just cover it up.

[Detling]

I have a small 20 watt panel connected via a split charge diode. The batteries are the starter and the bow thruster battery, these are feed by one alternator, the second alternator charging the domestic bank. As it is a small panel it does not need a controller and the 0.7 voltage drop is not a problem, the idea is to keep the batteries topped up mainly in the winter when the boat can spend several weeks with no attention.

 

If you use a voltage sensitive relay to connect the banks they will spend most of the day connected, as even on a dull day in winter the mppt is going to provide about 13 volts, enough to close the relay.

 

I can think of no way of connecting both controllers to both banks that keeps the discharge currents separate.

[Chalky]

 

Also 'split charge diodes' are not advised as they cause a volt drop, usually a 'split charge relay' is advised

 

You'll loose about 0.7V in each diode. There are ways round this using Mosfets and some controllers use these instead of diodes. If you want to split charge using solar then find a solar controller that supports this. Alternatively use 2 panel arrays, 1 for the engine start and one for the domestic. It's what I've done.

 

If you use a voltage sensitive relay to connect the banks they will spend most of the day connected, as even on a dull day in winter the mppt is going to provide about 13 volts, enough to close the relay.

 

 

However you'll use power to run the voltage sensitive switch in the relay and if it is a relay about 100ma just to switch the coil. Mosfets (transistors) are more efficient.

[Baloo]

Chuffed with the speedy responses fellas.

 

To clarify I have one start batt and 40amp alt which I am leaving as is.

 

The domestic bank of six I am splitting into two banks is currently charged by 150 amp alt + travel power through victron combi. .....

Why? We'll I'd like to give it a try. I can always revert back just by selecting 'both' if it proves detrimental.

I think that having a more versatile system of wiring for batteries has advantages which I'd like to experiment with.

 

I like the idea of taking two batts out of service and 'giving them a break in the sun' as it were, perhaps using each bank on alternate days, probably more likely to achieve somewhere near a 100% SOC that way.

 

Alternatively I like the idea of keeping four in good nick for general use, (fridge freezer, lights, TV Etc), and switching over to the other two (expendables) for less frequent but more demanding usage, ie microwave, Washing machine (with engine running and travel power I think that there is still quite a draw from the batts when the immersion heater kicks in.)

 

Replacing only four rather than six when time comes certainly sounds good, then maybe the best two might find their way over onto the pair.

 

Maybe in future I can try having two traction batts and four wet lead acid.

 

Anyway a relay rather than a diode you say? I haven't heard of them before, I shall have a look into those, can anyone recommend one? I didn't see them in midland chandlers today, not to say they weren't there. It's an hours drive each way to Braunston so I might fit my new diode to the engine start alternator and save the diesel money rather than return it for £35.

[Chalky]

If you do fit the diode then you'll undercharge your batteries or it will take longer to charge them. This is because you'll loose 0.7V at the diode, so if your alternator regulates at 13.4V (old standard) your batteries will never see more than 12.7V and that's not allowing for the voltage drop in your cables. There are 3 ways round this (all are on the smart gauge website.)

• Fit a regulator that regulates to something like 14.4V - you may already have this. You still have the volt drop but you have a bit more headroom to play with. Not perfect but it will work.
• Fit a tractor regulator. These have an extra wire that you connect to the batteries. This changes the alternator from machine sensing to battery sensing which means that it will measure the voltage after the diode. What it will do is wind up its output until the batteries see the required voltage.
• Fit a split charge relay. These come in a number of flavours but in effect they join the two batteries together once the engine is running or the alternator voltage reaches a pre-determined level.

All will work. Split charge relays have been round for years - we were fitting them onto Land Rovers in the 80s.

Edited September 23, 2014 by Chalky

[bottle]

Baloo

 

You experiment if you want to but this has come up before and one bank correctly charged is the way to go.

 

when you split a bank, the bit that is working, has to work harder to compensate for the bit that isn't there.

 

so the bit that is working discharges more and so needs a longer charge time

 

Simply and disregarding all other factors,

 

two 110 amp.hr batteries supply say 50 amp.hrs, each battery supplies 25 amp.hrs

 

four 110 amp.hr batteries supply say 50 amp.hrs each battery supplies 12.5 amp.hrs.

 

six 110 amp.hr batteries supply say 50 amp.hrs each battery supplies 6.25 amp.hrs.

 

You still have to put back 50 amp.hrs plus a bit (losses in charging system) in all cases.

[Baloo]

If you do fit the diode then you'll undercharge your batteries or it will take longer to charge them. This is because you'll loose 0.7V at the diode, so if your alternator regulates at 13.4V (old standard) your batteries will never see more than 12.7V and that's not allowing for the voltage drop in your cables.

This doesn't make sense to me, or are you talking about my engine start battery....Just by fitting the diode to the 40amp alternator so that that alt is shared between the engine start and domestic bank(s)? I'll still have the 150 amp alt connected directly to whichever (or both) of the domestic banks is selected by the switch.

[RLWP]

This doesn't make sense to me, or are you talking about my engine start battery....Just by fitting the diode to the 40amp alternator so that that alt is shared between the engine start and domestic bank(s)? I'll still have the 150 amp alt connected directly to whichever (or both) of the domestic banks is selected by the switch.

 

Your starter battery will be charged to 0.7V less than without the diode - it will never exceed 12.7V. And that last 0.7V represents quite a lot of charge i.e. energy stored in the battery

 

Richard

Edited September 23, 2014 by RLWP

[Baloo]

Baloo

 

You experiment if you want to but this has come up before and one bank correctly charged is the way to go.

 

when you split a bank, the bit that is working, has to work harder to compensate for the bit that isn't there.

 

so the bit that is working discharges more and so needs a longer charge time

 

Simply and disregarding all other factors,

 

two 110 amp.hr batteries supply say 50 amp.hrs, each battery supplies 25 amp.hrs

 

four 110 amp.hr batteries supply say 50 amp.hrs each battery supplies 12.5 amp.hrs.

 

six 110 amp.hr batteries supply say 50 amp.hrs each battery supplies 6.25 amp.hrs.

 

You still have to put back 50 amp.hrs plus a bit (losses in charging system) in all cases.

Thanks Bottle. I know a little knowledge can be a dangerous thing. I suppose my thinking has been along the lines of 4 batts to use, and 2 to abuse! Maybe I haven't given you enough background on my charging routine though. For example in the winter, every 2nd morning Mrs Baloo puts the engine on for 15min to use hair dryer. Then knocks it off again so she can walk the dog ! Hardly ideal but up until now use of hair dryers without engine running has been prohibited, as has leaving a running engine unattended.

I know a little genny is an obvious solution to that instance but I really don't to have one to store, or petrol on the boat.

[Baloo]

Your starter battery will be charged to 0.7V less than without the diode - it will never exceed 12.7V. And that last 0.7V represents quite a lot of charge i.e. energy stored in the battery

 

Richard

Thanks, I'll return it then, I think with the travel power as well as the other two alts I have plenty of power available, when the engine is running.

The issue is splitting the solar charge. I shall try one of these.

http://www.midlandchandlers.co.uk/Catalogue/ProductList/relay?catalogueLevelItemID=95666104-74fe-473f-98fb-00a2cb68d355

[bottle]

Thanks Bottle. I know a little knowledge can be a dangerous thing. I suppose my thinking has been along the lines of 4 batts to use, and 2 to abuse! Maybe I haven't given you enough background on my charging routine though. For example in the winter, every 2nd morning Mrs Baloo puts the engine on for 15min to use hair dryer. Then knocks it off again so she can walk the dog ! Hardly ideal but up until now use of hair dryers without engine running has been prohibited, as has leaving a running engine unattended.

I know a little genny is an obvious solution to that instance but I really don't to have one to store, or petrol on the boat.

 

You are doing a lot of damage to your engine by only running it for 15 minutes than trying to change the battery set up will save.

 

Even given the above usage one large bank is better than two smaller ones

 

No engine should be started for less than it takes to get it up to temperature plus a bit.

 

Depending on size of Mrs Baloo's hair-dryer then the batteries and the inverter should be able to cope.

 

If not, four solutions, Mrs Baloo stops using hair-dryer, Mrs Baloo has shorter hair, Mrs Balloo uses a towel or the hair-dryer is changed to a lower wattage one.

 

Just thought of another solution, Mrs. Baloo washes and dries her hair when ever you are charging the batteries.

 

The best way to charge your batteries would be with a charger run from the Travel Power

 

You have a generator already onboard, the Travel Power.

 

Now on a completely different track the solar and controllers need sorting.

 

It may be possible to make them into one solar bank and with a suitable controller keep the domestics topped up.

 

Your start battery should be able to cope on its own, it should be able to stand there for about three months without to much detriment but of course when you run your engine to power the domestic alternator and the Travel Power it will receive a charge from its own alternator, no need to connect it to the solar.

 

Note: the piece in italics, please let me know when you are going to tell Mrs Baloo, as I need to plan to be out of the country.

[smileypete]

For example in the winter, every 2nd morning Mrs Baloo puts the engine on for 15min to use hair dryer. Then knocks it off again so she can walk the dog ! Hardly ideal but up until now use of hair dryers without engine running has been prohibited, ...

 

Um, why? Is it that the batts are in poor condition or sulphated?

 

If you have 600Ah of leisures then that's about 3kWh to play with, so 15 mins on a 1200W hairdryer is about an eighth of that.

 

More/better batts would be cheaper than an engine overhaul, or a divorce! If there's a travelpower and big combi, it should recharge a big bank fine.

 

Sounds like you're living aboard off grid, maybe a one or two 1-2hr charges mid week and a looong 6-8 hour charge/cruise at weekends to keep the batts in good nick, especially in winter when solar is in short supply.

 

Gotta be better than killing the engine with short 15m runs where it's barely warmed up. Consider upping the solar considerably next spring too, and doing some power auditing with clamp meter in the meantime...

 

cheers, Pete.

~smpt~

Edited September 24, 2014 by smileypete

[MtB]

How many 15 minutes runs does it take to kill a modern jap digger engine then?

 

Many thousands I suggest....

 

MtB

[casper ghost]

Removed, to ask question in a new thread.

 

Casp'

Edited September 25, 2014 by casper ghost

[smileypete]

How many 15 minutes runs does it take to kill a modern jap digger engine then?

 

Many thousands I suggest....

 

MtB

 

Well I didn't really mean KILL but not going to do it much good.

 

Though I have to admit I did slip below my usual standard of CWF pedant proofing there.

 

Slight rant here, but it's a sign of the times when you can give some well reasoned advice, then someone comes a long and nitpicks in in a one liner, and gets a greenie for it, FFS!!!

 

So what do you suggest the OP do?

 

cheers, Pete.

~smtp~

Edited September 25, 2014 by smileypete