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The Mad Cat
27-01-2016, 05:27 PM
Optima recommend to charge their batteries at a maximum of 10 amps. So if I have 2 batteries of equal condition in parallel and use a 20 amp charger does this mean each battery will only receive 10 amps or will they receive 20 amps each, being that they are in effect one battery when wired in parallel.
I have had 2 conflicting opinions from 2 auto sparkies and tried an internet search but can't find an answer.
Any help appreciated.

TMC

Noelm
27-01-2016, 05:57 PM
Be hard to get 40 amps out of a 20 amp charger!

The Mad Cat
27-01-2016, 06:07 PM
Be hard to get 40 amps out of a 20 amp charger!


Yes the word "each" probably shouldn't be there Noelm but the next part of the sentence clarifies what I mean. See below.

"being that they are in effect one battery when wired in parallel"

Kero
27-01-2016, 06:09 PM
Each battery will only draw the amount of current that it needs. As long as the charging voltage is correct, you can't force current through them by using a bigger charger. As their level of charge increases, the current flow will decrease.
The only problem you may encounter is if you are using a smart charger as it will most likely react to the current flow from the battery with the least charge.

scottar
27-01-2016, 07:38 PM
They will only get half each - provided your cables and connections between them do not provide resistance.

trevs1979
27-01-2016, 07:55 PM
They will only get half each - provided your cables and connections between them do not provide resistance.

100% percent correct in most cases once one battery starts to fail it drains the other to a point of no return anyway

think of it like this two batteries that are the same make and model should have the same or very close values of the following
(1) internal resistance
(2) unload and loaded voltages
(3) max cca should result in very similar voltage drop

both the above are the same reason you should never parallel different battery types or brands or cca sizes as these values will be different and load draw wont be equal nor correct charge ratio

because of this your charging load should and will in most cases spread evenly across both batteries (ie) half your rated max charge current rating from what ever charger you buy so .......10 amps each battery give or take an amp or two which is harmless

tjotter
27-01-2016, 08:26 PM
Fullriver 105amp agm's in parallel here, charged with a Matson 2-24amp charger,
the charger has a readout & I have never seen it say it is pushing more than 3 amps.

10 amps might be near the limit of a household powerpoint ?

trevs1979
27-01-2016, 09:26 PM
Fullriver 105amp agm's in parallel here, charged with a Matson 2-24amp charger,
the charger has a readout & I have never seen it say it is pushing more than 3 amps.

10 amps might be near the limit of a household powerpoint ?

when talking batt chargers or anything with voltage stepped up or down best off thinking of input power vs output power in watts so

standard power point 240 volt @ 10amps = 2400 watts max assuming unity pf
that would give you the following potential output charge currents although single phase chargers are never going to be this big and the equipment would also suffer loses

6 volt 400 amps
12 volt 200 amps
24 volt 100 amps

regardless its never going to be a problem

ranmar850
27-01-2016, 11:49 PM
Don't confuse the charging current with the 240v draw from the outlet, as one poster above seems to. 10A @13.7v into your battery will likely be drawing about (roughly)1amp from your 240v supply, or a little more due to losses in the charger. As an example, I can run a 50A charger running near full noise from a750w (900 w peak) generator. This generator will output less than 4A.

Crunchy
28-01-2016, 08:59 AM
Each battery will only draw the amount of current that it needs. As long as the charging voltage is correct, you can't force current through them by using a bigger charger. As their level of charge increases, the current flow will decrease.
The only problem you may encounter is if you are using a smart charger as it will most likely react to the current flow from the battery with the least charge.

I would have thought the other way around, the charger will "See" a fully charged battery when one of them is fully charged even if the other battery is under-charged therefore it will swtich to trickle or maintenence mode and potentially leave one battery undercharged. This happend to me, I used to charge in parallel and the smart charger was telling me all was sweet but when I looked into it one day one of the batteries was actually totally stuffed. I now charge each (New) battery seperately until full then switch to parallel for mantenence / storage. Make sense?

Kero
28-01-2016, 09:18 AM
I would have thought the other way around, the charger will "See" a fully charged battery when one of them is fully charged even if the other battery is under-charged therefore it will swtich to trickle or maintenence mode and potentially leave one battery undercharged. This happend to me, I used to charge in parallel and the smart charger was telling me all was sweet but when I looked into it one day one of the batteries was actually totally stuffed. I now charge each (New) battery seperately until full then switch to parallel for mantenence / storage. Make sense?

You may well be right! I'm not sure whether the charger is sensing voltage or current. If it's sensing voltage then it will react to the fully charged battery.

LoungeLizard
28-01-2016, 10:13 AM
Unless both batteries are in good condition and the initial voltages are very similar, connecting two batteries in parallel is a bad idea. Once they are connected, some current will flow from the battery with the higher voltage to the one with the lower voltage, until the voltages are equal. If there is a significant difference in the voltage the current flow can be very high which may cause all sorts of issues: Explosion, cables melting etc. I've seen this first hand, some guy at work connected a 24V truck battery to a 12V battery ... brown pants everywhere.

When the voltages have been equalised it becomes one "big" battery. The charger will charge it as usual, but it will take twice as long.

Crunchy
28-01-2016, 11:13 AM
The issue I had was that one battery had dropped a cell (Check your electroyte at the beginning of summer!) but because they were connected in parallel the smart charger didn't pick up on it, when I connected individually the smart charger came up error light after a while.

odieman150
28-01-2016, 01:47 PM
Just a question guys, do the dual battery kits charge both the batteries evenly when put on the charger?

Rip it up
28-01-2016, 04:00 PM
I run a redarc sbi12 dual battery smart isolator in the boat. 2x century marine batteries equal in size.

And yes my ctek 5A charger will argue both batteries equally when connected straight to the terminals of the starting battery.

I leave the charger on for a few days on a standard charger mode and both batteries level out at 12.7 after charging is complete.


Damo's dodgy boat building repair shop.

TheRealAndy
28-01-2016, 04:46 PM
Parallel batteries of the same/type size are fine. In typical disclaimer type I always say use a fuse/fusable link between the 2. Trucks been doing this for years. Provided both are in good nick, they will take an equal charge each. As crunchy said, a dropped cell will mean one wont charge properly, but a quick check of each battery with a multimeter every so often will pick this up.

Lovey80
31-01-2016, 11:53 AM
Andy do you see any problem in doing this when the batteries are different if both batteries are topped up before they are switched in parallel? Example is a cranking battery and a deep cycle battery that you want to keep topped up if there's a long time between uses.

tjotter
31-01-2016, 07:39 PM
I think a cranking battery & a deep cycle battery will have different charging requirements and they will have different voltages once fully charged.

Some batteries are happy to be maintained on a float mode/trickle charge and I have been told some should not be floated long term.

A cranking battery & a deep cycle battery may have a different voltage when flat and probably a different sensitivity to being heavily discharged, eg below 50%. Does this answer your question Lovey80 ?

You can do what you like to your batteries, just that if you look after them they will probably last longer.

The dealer I bought my batteries from told me the 'charged' voltage, and the 'flat' voltage for each battery.
A good charger does it automatically, no need to worry about charged voltages.

scottar
31-01-2016, 08:05 PM
While probably not the "recommended" thing to do, I can't see it being a major. I ran a N70 size lead acid and a 75 amp AGM side by side in parallel for several years in my last tinnie due to space constraints. They were used as combination starting / electric motor batteries as I wasn't worried about flattening them - the engine pull started very easily if required. They were charged from the same 20 amp Super Cheap charger via the feed for the electric when flattened without any dramas at the time (none that physically presented themselves anyway). They may not have been charging to full capacity but certainly didn't present any issues with holding enough charge for some pretty big sessions at Awoonga. I did eventually replace the N70 with a 100 amp AGM but the 75 amp battery was still going strong at 7 years old when the boat was sold.

tjotter
31-01-2016, 08:08 PM
thanks scottar, it's good to know a real story cf to a manufacturers recommendation.

seashawgal
31-01-2016, 08:10 PM
There is a very good little book explaining all about batteries called "batteries in a portable world"

Kevin Ferguson
01-02-2016, 07:23 PM
TMC

Unsure which Optima's you are running , however 10 Amps is not required. Optima recommend 4 Amps constant with a time period subject to state of charge.

Red Top (34 type) - 12-45 to 12-55 V 4Amps / 4 hrs. Yellow Top (34 type) - same voltage range 4 A / 6 hrs.

Blue Top (D34M) - Same as Yellow Top. Yellow Top (D31A , D27F) Blue Top (D27M , D31M) - same voltage

range 4 A / 9 hrs.

I don't believe that the charger that you would be using would put out a constant charge , but would be 1 that will decrease the rate of charge as batteries approach full charge going into float at completion of charge.

Voltages after 24 hrs. stand should be 12-8V for Red Top or 13-1V for others. Just check Voltages before charging & charge in parallel if similar state of discharge.

As to mixing & matching of batteries types during charging NOT recommended. You can get away with it as Scottar stated (trickle charges being used by most). Just not on my boat or in my vicinity.

Cheers Kevin.

TheRealAndy
01-02-2016, 09:09 PM
Andy do you see any problem in doing this when the batteries are different if both batteries are topped up before they are switched in parallel? Example is a cranking battery and a deep cycle battery that you want to keep topped up if there's a long time between uses.

I wouldn't do it long term, but yes you can do it. Fuse between the 2 as standard disclaimer.

The best way to do is with something like this http://www.gsl.com.au/battery-chargers-12v-12v.html Not cheap, but will ensure optimum charging of batteries. DC-DC chargers dont get anywhere near the love they deserve.

Lovey80
01-02-2016, 09:17 PM
Yeh I guess I wasn't clear.

Basically what I want to be able to do is the day before I store the boat long term I want to charge each battery individually to full. Then so I don't have to run two chargers at the same time in the same boat. I want to switch them into parallel and pop the charger onto one battery to keep both batteries maintained befor putting the cover on and storing it in the shed for what could be months so I don't come home and find one completely dead like last time.

fisho64
02-02-2016, 12:10 AM
Be hard to get 40 amps out of a 20 amp charger!
not sure if you are just being sarcastic Noelm but it certainly is possible to get "40 amps from a 20 amp charger".
If you have two 12 V batteries in series (24V) and you put 20 amps at 24V into the pair, EACH will receive 20 amps at 12 volts.

Noelm
02-02-2016, 05:08 AM
Yes, I was just being silly, probably should have explained the parallel business......but seeing as in series, or 24V was never mentioned, just thought it was redundant.

TheRealAndy
02-02-2016, 09:43 AM
not sure if you are just being sarcastic Noelm but it certainly is possible to get "40 amps from a 20 amp charger".
If you have two 12 V batteries in series (24V) and you put 20 amps at 24V into the pair, EACH will receive 20 amps at 12 volts.

Nah, that wont happen. If a charger is rated at 20Amps, all it will supply is 20amps. Try for more and you will pop the chargers fuse or trips its protection mechanism. Each battery is still drawing 20amps, its just at half the voltage!


The key to remember here is, you are not "putting" current into a battery, the battery is 'drawing' current from the charger.

As the battery becomes more charged, it draws less current. If you have a damaged battery (shorted cell) it may well draw more current.

The next problem arises because a smaller battery WILL draw more current than it can handle to become charged. This is why we restrict the amount of current available to smaller batteries. Larger batteries also have a limit, but you often find that even with large chargers you are sill way below that limit.

So hooking smaller batteries in parallel with large batteries is generally frowned upon, because the differences in how much current they draw when becoming charged. It can also be a fire risk if the smaller battery becomes discharged and then draws more current than it can handle from the bigger battery. This is why I always say use a fuse between parallel batteries.



I might see if I can find some cheap ammeters on ebay and do some experiments with photos for you all. I have 2 12V deep cycles for camping, one AGM and one flooded. Would be ideal to demonstrate the issues.

Kevin Ferguson
02-02-2016, 03:33 PM
Alzheimer's kicking in again. Voltage range from previous post should be 12-5 V to 12-64 v. Amps & hours correct. Proof that I am "right" 50% of the time.

Cheers Kevin.

Noelm
02-02-2016, 03:49 PM
When "things" get in series a whole new set of rules apply, anywhere in the circuit, you can insert an amp meter and measure your 20 amps, measure in 4 different places does not mean you have 80 amps! Now back to parallel, Andy is correct.

TheRealAndy
02-02-2016, 06:22 PM
When "things" get in series a whole new set of rules apply, anywhere in the circuit, you can insert an amp meter and measure your 20 amps, measure in 4 different places does not mean you have 80 amps! Now back to parallel, Andy is correct.

I dont like my explanation though, ie where I said each battery is drawing 20amps. Not technically correct, but as far as the current source (charger) is concerned it looks like one 24v battery that will be drawing 20 amps. I could not think of easier way to describe it.

Noelm
02-02-2016, 08:12 PM
It is very hard to explain in home handy man terms what you spent years learning from text books and teachers, and you know inside out in your mind, putting into text just muddles things sometimes.

aussiebasser
02-02-2016, 10:12 PM
Buy two little C-Tek chargers to maintain the batteries when stored.

scottar
02-02-2016, 10:27 PM
It is very hard to explain in home handy man terms what you spent years learning from text books and teachers, and you know inside out in your mind, putting into text just muddles things sometimes.

I don't know about that Noel - this bloke does a good job LOL

http://www.bing.com/videos/search?q=turbo+encabulator&view=detail&mid=1A544A9B51C9C9EC83F71A544A9B51C9C9EC83F7&FORM=VIRE6

The Mad Cat
03-02-2016, 06:31 AM
TMC

Unsure which Optima's you are running , however 10 Amps is not required. Optima recommend 4 Amps constant with a time period subject to state of charge.

Red Top (34 type) - 12-45 to 12-55 V 4Amps / 4 hrs. Yellow Top (34 type) - same voltage range 4 A / 6 hrs.

Blue Top (D34M) - Same as Yellow Top. Yellow Top (D31A , D27F) Blue Top (D27M , D31M) - same voltage

range 4 A / 9 hrs.

I don't believe that the charger that you would be using would put out a constant charge , but would be 1 that will decrease the rate of charge as batteries approach full charge going into float at completion of charge.

Voltages after 24 hrs. stand should be 12-8V for Red Top or 13-1V for others. Just check Voltages before charging & charge in parallel if similar state of discharge.

As to mixing & matching of batteries types during charging NOT recommended. You can get away with it as Scottar stated (trickle charges being used by most). Just not on my boat or in my vicinity.

Cheers Kevin.

HI Kevin,
This is off the Optima site.
https://www.optimabatteries.com/en-us/support/battery-care/charging
I am running 4 blue tops, 2 as house and 2 as start. The blue tops are hybrid like the yellow tops and was trying to look after them by following Optimas recommendations. I really don't understand as much about all of this as i would like, hence the original question and thanks to everyone for there reply's.

TMC
Battery Charger:


13.8 to 15.0 volts, 10 amps maximum, approximately for 6-12 hours.

Battery Charger:

Kevin Ferguson
12-02-2016, 08:24 PM
TMC

Apologies for not replying sooner. Had a look at Optima site via your link. I think that this would be for general public & the chargers that they would have normal access to. Specs I have provided are from Optima but relate to commercial charging applications. I top up charge Optima's on a regular basis using either 4 channel - 70Amps per channel or single channel 270 Amp output rectifiers. Constant current for the entire charge time allocated.

Your blue tops are usually charged in 6 banks of 6 (36 per channel) @ 4 Amps (total input 24 amps). As mentioned on their site heat build up is an important issue. Should not be a problem for you. I have a laser temp gauge to monitor 'on charge' product to avoid overheating with resultant venting thru the valve.

I can appreciate you wanting to keep them in prime condition as they are an expensive product. I rate them highly & see virtually nil warranty claims unless from abuse. As per your original post re keeping them on a constant float charge consider this , commercial battery manufacturers / wholesalers do not keep their stock on a continual charge. I would be charging them to full capacity , disconnecting all cables & would have no problems leaving them sit for the 1 to 2 months you mentioned.

Cheers Kevin.

Noelm
13-02-2016, 07:58 AM
Any battery that can't sit for a few months and still be OK is near shagged.

Fed
13-02-2016, 10:10 AM
It would probably help to know exactly what batteries & charger you have TMC.

The Mad Cat
15-02-2016, 08:13 PM
It would probably help to know exactly what batteries & charger you have TMC.

Hey Fed,
I think it was mentioned somewhere. Optima Blue Tops 2 house and 2 start. I only have a smaller Ctek 3.5 amps I think it is, so was looking for something more suitable to run off a small gen set when/if needed when we are away for longer trips and something to top up batteries when at home. Batteries will be running a fridge and freezer plus lights, fans etc.

TMC

Fed
16-02-2016, 11:11 AM
There is 2 types of blue tops mentioned in the link but looking more carefully the charging is much the same for both.

I'd be looking for a charger big enough to do the job under the flattest conditions (20A) that also has a built in Voltmeter & Ammeter.
Then get to 'know' your batteries & stop charging when they're full, I have to say I've never been a fan of leaving batteries on trickle/float charge simply because I think it can mask a problem.

FWIW there seems to be heaps of stand alone digital Voltmeter/Ammeters available on the net, cheap as chips.

The Mad Cat
18-02-2016, 09:01 AM
http://www.ctek.com/au/en/Product/Category?category=sailboat

The Ctek M300 is my choice so far. Other opinions welcomed.

TMC

juggernaut
18-02-2016, 09:13 AM
I have the M300 and a Redarc SBC1205.

http://www.redarc.com.au/products/product/smart-battery-charger

The M300 does put some heat into the batteries and certainly need to vent the area where you are charging due to the gasses the batteries gives off. For this reason I prefer the Redarc. Both great chargers. The M300 does have the recondition mode for dead batteries which I have used from time to time for mine and friends batteries and works a treat to bring batteries back to life.