Two chargers to a single SLA? - Page 1
Forum section: electronics / projects

author: DTJ
author_rank: Super Contributor
timestamp: January 31, 2019, 01:05:32 pm
content: I've got a setup with a 195W solar panel charging a 40Ahr (2x20Ahr) SLA battery. It uses a Powertech 10A PWM solar charge controller.I also want the option to charge it from a mains SLA charger - possibly at the same time.This is the mains powered charger:https://www.jaycar.com.au/3-stage-6-12-battery-charger/p/MB3609What would be the consequences of connecting the two chargers in parallel?My guess is that it would probably be ok... maybe.

author: NorthGuy
author_rank: Super Contributor
timestamp: January 31, 2019, 03:50:48 pm
content: I have 3 chargers on my batteries - 2 solar and one AC. The only problem I can think of is too much current into the battery, but since I don't use the AC charger in full sun, this is not a problem for me.

author: Clint_dk
author_rank: Newbie
timestamp: March 06, 2019, 06:01:23 pm
content: I would not chance it. However maybe add a change over switch where you can manually switch between the two, or an electronic switching system that runs the solar charger, and then switches to the ac charger if the solar chargers voltage drops.

author: coromonadalix
author_rank: Super Contributor
timestamp: March 06, 2019, 06:08:09 pm
content: I would never put 2 chargers in parallel, it may create more problems, create problems with timings / currents sensing ... some intelligent charger need to sense the battery, instead use somekind of relay switching to isolate the unneeded chargerOk some relays switching when on dc input or ac input ??

author: Gregg
author_rank: Super Contributor
timestamp: March 06, 2019, 10:45:33 pm
content: Again, the answer is, “it depends”. From my experiences with telco battery systems of up to 15 paralleled chargers of different dates and manufacturers, unless there is some form of load share, the charger with the highest potential will provide the most current. It is critical that paralleled chargers have some type of current limiting, are immune to back feeding and individually fused. Load sharing is probably beyond the scope of what most home solar manufacturers would consider marketable.I have seen 5000 amp systems at 54 VDC where a few 400 amp chargers were running in current limit at 440 amps and others were running less than 100 amps. The only problems occurred when paralleling switch mode chargers with some of the old school linear chargers whose old capacitors couldn’t handle the high frequency ripple fed back to them.

author: coromonadalix
author_rank: Super Contributor
timestamp: March 06, 2019, 11:00:13 pm
content: yeah but the load share etc... is mostly done in the server psu classHaven't seen that in "normal" sla chargers

author: Gregg
author_rank: Super Contributor
timestamp: March 07, 2019, 02:45:09 am
content: I mainly brought up load sharing because I think there may be a demand for solar and mains battery chargers to both be connected to a string of batteries like the OP stated. With the price of electricity climbing, a few people want long term reliable mitigation rather than the cheapest possible solution. Load sharing is proven and reliable technology in the hot swappable switch mode charger industry. Here is an example of a "normal" systemhttps://www.eltek.com/products/flatpack2-ps-system/.In many of the large data centers the equipment connecting the data center to the internet is battery backed DC powered because it is an order of magnitude more reliable than AC UPS systems. It is always on; no switching required if the utility power goes off.

author: DTJ
author_rank: Super Contributor
timestamp: March 07, 2019, 04:47:57 am
content: What I ended up doing was having the two chargers in // but only enabling one of them at a time.The solar charge controller is a PWM output and understandably it doesn't play well with a mains SLA charger powered at the same time.