Engine battery charging question.

[canals are us?]

Some time ago I bought a cheap 20amp 3 stage battery charger from electroquest and it's doing a great job at charging my 2 new 6v Trojan T105's.

 

I was thinking can I also wire the charger so it charges the engine starter battery? Is it a simple case of wiring new cables from the charger to the battery? On my charger I cut the crocodile clips off and used terminal strips to extend the wire to the batteries. Could I just wire in a live and neutral from the terminal strips to the starter battery and install another in-line fuse at the live feed to battery?

 

On the live from the charger to the Trojan leisure batteries I have an inline fuse. What size fuse would I need from charger to engine start battery?

 

Thanks James

[Keeping Up]

You can charge one or the other, but you cannot connect or charge them both at the same time because in trying to do so you are in effect connecting the batteries to each other through thin wires that aren't suitable for that purpose (well strictly speaking you can do it but it's not as simple as just connecting them together)

[Alan de Enfield]

Unless your charger has two-outputs then all you are doing is conecting your domestic bank and the engine battery together.

 

If you are wanting a simple and just a 'topping up' method - just get a standard jump lead and link the +'s on the domestic and the starter batteries - just remember to disconect it when starting the engine, or running the domestics with a heavy load - otherwise you'll be taking it out of the domestics. - when you start the engine - or out of the starter battery when you are loading the domestics.

[cereal tiller]

Some time ago I bought a cheap 20amp 3 stage battery charger from electroquest and it's doing a great job at charging my 2 new 6v Trojan T105's.

 

I was thinking can I also wire the charger so it charges the engine starter battery? Is it a simple case of wiring new cables from the charger to the battery? On my charger I cut the crocodile clips off and used terminal strips to extend the wire to the batteries. Could I just wire in a live and neutral from the terminal strips to the starter battery and install another in-line fuse at the live feed to battery?

 

On the live from the charger to the Trojan leisure batteries I have an inline fuse. What size fuse would I need from charger to engine start battery?

 

Thanks James

Maybe connecting the charger to the engine battery with a Voltage Sensitive Relay would work?

 

These can be obtained for @ 12 pounds,i got a couple from a company called Brocott in the UK.30 amp rating.

 

the relay would connect the batteries together at 13.2 volts and disconnect if that voltage were reduced by cranking engine,or could be disabled by a 5 pin relay switched by adding an extra connection to the start switch/button.

 

Might be prudent to install a fuse as well

 

CT

[canals are us?]

Thanks for the very quick replies.

Never as simple as you would like!

I think the easiest, cheapest and safest is just to run the engine for an hour every few months to top up the starter battery. I'm Marina based so ATM engine not being used. Beta 1305. 35hp. I started it today and it fired up on the second crank. Probably not a great starter battery as no idea on the age.
I always switch off the battery charger while I have the engine running.

James:cheers:

Edited February 15, 2014 by canals are us?

[cereal tiller]

Thanks for the very quick replies.

 

Never as simple as you would like!

 

I think the easiest, cheapest and safest is just to run the engine for an hour every few months to top up the starter battery. I'm Marina based so ATM engine not being used. Beta 1305. 35hp. I started it today and it fired up on the second crank. Probably not a great starter battery as no idea on the age.

I always switch off the battery charger while I have the engine running.

 

James:cheers:

Silly question,but, are you sure the charger has only 1 positive output?

 

My boat has a 30 amp Electroquest charge which has 1 neg. output and TWO positive output terminals,thus allowing independent charging of 2 battery banks.

 

Maybe the 20 amp version has just the 1 pos. output?

 

CT

[canals are us?]

Silly question,but, are you sure the charger has only 1 positive output?

 

My boat has a 30 amp Electroquest charge which has 1 neg. output and TWO positive output terminals,thus allowing independent charging of 2 battery banks.

 

Maybe the 20 amp version has just the 1 pos. output?

 

CT

Looked online and mine only charges one battery bank.

https://electroquestuk.com/products/battery-chargers/leisure-battery-chargers-marine-battery-chargers/fully-automatic-3-stage-battery-charger-12v-20a.html?main_page=product_info&cPath=2_36&products_id=372

I can see this 30amp version charges two battery banks, so like yours.

https://electroquestuk.com/products/battery-chargers/leisure-battery-chargers-marine-battery-chargers/fully-automatic-5-stage-marine-battery-charger-12v-30a.html?main_page=product_info&cPath=2_36&products_id=318

 

One day when funds allow may upgrade.

 

James

Edited February 15, 2014 by canals are us?

[dmr]

To elaborate on what CerealTiller has said: there is a big thread in the equipment section on alternator paralleling which is exactly the same as battery paralleling which is what you are proposing to do.

A big relay and moderately thick cables are required, plus a foolproof means of making sure that the batteries are not connected together when they shouldn't be.

 

.............Dave

[cereal tiller]

To elaborate on what CerealTiller has said: there is a big thread in the equipment section on alternator paralleling which is exactly the same as battery paralleling which is what you are proposing to do.

A big relay and moderately thick cables are required, plus a foolproof means of making sure that the batteries are not connected together when they shouldn't be.

 

.............Dave

As in,voltage sensitive relay?

 

Look up "Ultimate Speed" battery charger,LIDL were selling them a few weeks ago and still available at @ 20 quid.

 

Have got one of these,fully automatic charge,max. 3.8 amps,can be left on permanently,would be the easiest to install.

 

would look after your engine battery just nicely.

CT

[Paul C]

There's basically 2 ways to do it:

 

1. Concede that the batteries are going to be connected, to charge both. This means that if the domestic bank are severely depleted but the engine/start battery is nearly fully charged, its not going to be charged and in fact some current may flow FROM it instead of TO it.

2. Get a battery charger with 2 outputs. (Or 2 battery chargers).

 

A diode or zero-volt-drop equivalent, or a smartbank, or a voltage sensitive relay, etc are all basically no.1 but with the extra capability to not connect the two batteries if the domestic batteries are much lower voltage than the engine/start. So, while the engine/start won't get charged, it won't get depleted. Only by having 2 independent battery chargers, or a battery charger with 2 independent outputs, can you charge 2 banks independently enough to eg put loads of power into a depleted bank at the same time as topping up a nearly full bank.

 

The above info is broad enough in scope to apply to and charging method, eg alternator(s), solar, mains battery charger.

Edited February 15, 2014 by Paul C

[blackrose]

Some time ago I bought a cheap 20amp 3 stage battery charger from electroquest and it's doing a great job at charging my 2 new 6v Trojan T105's.

 

I was thinking can I also wire the charger so it charges the engine starter battery? Is it a simple case of wiring new cables from the charger to the battery? On my charger I cut the crocodile clips off and used terminal strips to extend the wire to the batteries. Could I just wire in a live and neutral from the terminal strips to the starter battery and install another in-line fuse at the live feed to battery?

 

On the live from the charger to the Trojan leisure batteries I have an inline fuse. What size fuse would I need from charger to engine start battery?

 

Thanks James

 

I think you should have bought a more expensive twin output charger if that's what you wanted to do. You could always but a small 10 amp charger for your start battery.

 

http://www.ebay.co.uk/itm/Numax-12V-10A-Leisure-Battery-Charger-Caravan-Campervan-Motorhome-Marine-Boat-/321156058628?pt=UK_Campervan_Caravan_Accessories&hash=item4ac6648e04

[Eeyore]

 

I think you should have bought a more expensive twin output charger if that's what you wanted to do. You could always but a small 10 amp charger for your start battery.

 

http://www.ebay.co.uk/itm/Numax-12V-10A-Leisure-Battery-Charger-Caravan-Campervan-Motorhome-Marine-Boat-/321156058628?pt=UK_Campervan_Caravan_Accessories&hash=item4ac6648e04

Agree that the OP would have been better off with a larger charger to start with; and that a 10amp second charger would provide some redundancy if the 20 amp failed.

However something like http://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_10001_catalogId_10151_productId_895219_langId_-1_categoryId_255205#tab3 would be sufficient, and cheaper, allowing the OP plenty of time to save for (and reflect upon) any required upgrade.

Steve (Eeyore)

Edited February 16, 2014 by Eeyore

[Paul C]

Actually, just buying a 2nd charger (a small 10A one) isn't such a bad option, given that although probably a bit more expensive (buying separate 10A and 20A chargers) offers some redundancy if either should fail.

 

Another valid option is simply do nothing. If the engine start battery goes flat and the domestic bank is okay, jump start the engine from the domestic bank.

[smileypete]

Is the start batt sealed or unsealed?

 

If the latter a trickle charge from a small solar panel or trickle charger should keep it fully charged, or even a dumb car charger on a time switch to give it an hour or two of charge a week.

 

A sealed/maintenance free batt should hold it's charge for aaaages.

 

As long as the batt hasn't been used or charged for 24hrs, the terminal voltage should reflect it's state of charge well enough, anything over 12.7V is a fairly high state of charge.

 

cheers, Pete.

~smpt~

Edited February 16, 2014 by smileypete

[ditchcrawler]

If the OP is charging his Trojans well he could well overcharge his starter battery just by linking them.

[Alan Saunders]

If the OP is charging his Trojans well he could well overcharge his starter battery just by linking them.

Or a diode link would drop 0.6V, even a relay may drop 0.5V.

[FORTUNATA]

Some time ago I bought a cheap 20amp 3 stage battery charger from electroquest and it's doing a great job at charging my 2 new 6v Trojan T105's.

The system I have which I didn't wire up myself uses an inverter/charger. Unfortunately, no split charging was ever installed so if I flattened my domestic batteries (2 in parallel), I'd not be able to start the engine. Something I have to address later on.

However, perhaps in this case I'd be inclined to use an inverter/charger as one possibility and (simplest approach), install a relay. However, I was thinking about this quite a bit as with an inverter/charger you have two charging sources in operation. Normally the relay is activated by the ignition key so that both batteries are getting charged Via alternator when the engine is running. However, when ignition is off, the starter battery is not connected to the house batteries so cannot flatten.

However, there is still the inverter/charger to consider and this provides a similar charge to the alternator (or as your solitary charger). Some people are a bit wary of relays being used with inverters due to surges in the event when the domestic batteries are flat and the starter battery charged. Sould someone start the engine and activate the relay while the inverter is under load, current surges are triggered as batteries try to equalise with a resulting damaged relay.

in the end, I decided the diode isolator is the best option so long as voltage drop is across diode is taken into consideration.

 

 

 

 

 

 

I was thinking can I also wire the charger so it charges the engine starter battery? Is it a simple case of wiring new cables from the charger to the battery? On my charger I cut the crocodile clips off and used terminal strips to extend the wire to the batteries. Could I just wire in a live and neutral from the terminal strips to the starter battery and install another in-line fuse at the live feed to battery?

 

On the live from the charger to the Trojan leisure batteries I have an inline fuse. What size fuse would I need from charger to engine start battery?

 

Thanks James

Edited February 17, 2014 by FORTUNATA

[canals are us?]

Sorry for not replying earlier, but been on a course.

 

Yes, I should of bought the 30amp charger, but funds were low at the time, and I wasn't keyed up on the different functions of the chargers.

 

I will probably buy a 10 amp charger for the starter battery. I believe from memory it is a 95 amp hour sealed battery.

Diodes and relays go right over my head!

 

Thanks James.

Edited February 17, 2014 by canals are us?