Reply With QuoteBe hard to get 40 amps out of a 20 amp charger!
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
Be hard to get 40 amps out of a 20 amp charger!
Originally Posted by Noelm
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"
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.
Cheers,
Leigh (Kero).
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
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 ?
Transire vinus forticulus
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
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.
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.
Cheers,
Leigh (Kero).
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.
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.
Just a question guys, do the dual battery kits charge both the batteries evenly when put on the charger?
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.
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