Needed: Lead Acid Charger with Voltage Control of Bulk Charge Current - Page 1
Forum section: electronics / beginners

author: OB1
author_rank: Newbie
timestamp: May 01, 2023, 11:54:13 am
content: First time on the forum. About myself: I have one of Dave's Multimeters and have watched him progress from the very start. I'm 75 so I'm knocking on a bit but electronics was my first love back in the 1960's when I got my City & Guilds T4 in Industrial Electronics. Whilst I understand the techie stuff I am really just a beginner compared to those on the forum that have been lucky in life to stay with and enjoy electronics.Let me explain the need which is solar power related. A grid-tie inverter works with a surplus power diverter to ensure zero-export to the grid. Conventionally, the surplus power is sent to a hot water heater but in this case, it is diverted to a convection air heater as means of getting rid of the excess power. The amount of diverted power which is sinusoidal is available from an external CT sensor with a 0-10v dc output.In this way the first objective is met in that it achieves zero-export however the surplus energy is wasted. The second objective is to capture and store the surplus energy in a battery. For proof of concept a 12v lead acid battery is chosen although the principle would apply equally to other chemistries.The theory goes like this: the conceived mains powered battery charger is the output of a close loop proportional-integral arrangement where the CT controls the amount of power charging the battery. An increase in surplus power causes the bulk charge to increase which lowers the amount of available surplus power. A decrease in the amount of surplus power decreases the amount of bulk charge. In this way ‘none’ of the surplus power is wasted because it is all captured for later use.Charging the battery only takes place in complete charge discharge cycles. The battery under load has to fall to 50% SOC before it is disconnected from the load for charging. It is only connected to the load when fully charged and then after 5 hrs of float charge. There is no partial charging of the battery and there is no need to fill the battery as quick as possible it will fill in its own time according to the available surplus power available.Searching is not bringing up anything on voltage control of bulk charging essentially because the bulk charging has to happen as quick as possible. Is what is being proposed possible? Comments please.

author: Jwillis
author_rank: Super Contributor
timestamp: May 02, 2023, 05:04:33 am
content: What I'm getting is you have a solar array that produces more energy than you consume day to day. You want to store excess energy in a second bank of lead acid batteries? Or are you running directly off the array from a converter?A solar charge controller is all you need to charge lead acid batteries. But that still won't solve the excess. because once that battery bank is charge, your still producing more than you need.This is not a bad thing.

author: OB1
author_rank: Newbie
timestamp: May 02, 2023, 08:19:53 am
content: Quote from: Jwillis on May 02, 2023, 05:04:33 amHi JW, thanks for taking the time to reply. Yes, I have a dual two string 750W array, east west making it 1.5kWp. The arrays feed into a dual MPPT Ginlong Solis Grid Tie Inverter. This GTI can, butIS NOT, setup for zero-export using an external CT which would allow it to phase control its output such that no surplus energy was fed back to the grid, a requirement in some countries.My install is a standard G98 with an external excess power diverter, an Immerson MK II which subtracts the available solar power from self consumption and exports the difference to a 230v 2kW fanless air convection heater. In this way zero-export is achieved. A CT is attached to the feed or hot wire to the heater to indicate the level of available export power. At the moment no batteries are involved and all of the excess power is wasted as heat.What is needed is to capture the export power and store it within a 12v battery for proof-of-concept purposes. On success the 12v battery will be replaced with a 48v bank of four 12v batteries probably lead acid to further develop the technique. Not sure it is a wise thing to connect a solar charger to the array in parallel with a connection to a GTI as conflicts would most likely occur. The array has to have an exclusive connection which is this case is to a grid tie inverter.

author: vk3em
author_rank: Contributor
timestamp: May 04, 2023, 11:40:05 pm
content: Bulk charging of Lead Acid cells is normally constant current, so the battery charger control loop is driven to achieve a fixed current.In multi-stage chargers, like the UC3906/BQ24450, when the bulk charge current starts to decrease, the charger swaps from bulk charge mode to over charge mode (voltage controlled). This is to ensure the maximum charge current at any point does not exceed C/10.Luke

author: OB1
author_rank: Newbie
timestamp: May 05, 2023, 07:18:07 am
content: Quote from: vk3em on May 04, 2023, 11:40:05 pmThanks Luke that was helpful but alas it does not provide a way forward. Whilst CC is associated with bulk phase charging a look at published charging curves for lead-acid shows the current falling as it approaches saturation point of 14.4v. This contrasts with Lithium charging where the 'curve' is flat CC as charging progresses to the constant voltage point where it drops vertically to the maintaining charge.Eugene Palatnik by way of an example published a novel design forvoltage control of currenton the Electronic Design website. Its this sort of control that is required to control bulk charge current. My research is turning up nothing at least I cannot find an off the shelf lead acid charger with voltage control of current.