Regulating the output of a dynamo (DC generator) to charge a battery - Page 1
Forum section: electronics / projects

author: 3Deye
author_rank: Contributor
timestamp: March 02, 2016, 09:35:39 am
content: Hi,I have a 3kW dynamo (DC generator) that is connected to an electromechanical regulator which are used to charge a 24V 100 Ah lead acid battery.I have no experience at working with dynamos and unfortunately I don't have its model number. I need to design an electronic regulator to replace the electromechanical one. From several readings on the internet I understood that (and please correct if I am wrong) the dynamo has 3 connections:1. "D" which is the output voltage/current of the dynamo.2. "F" which is the input field current.3. Ground.The dynamo will generate excessive voltage and current when it's RPM is increased by the engine, that's why the "F" connection should be used by the regulator to increase/decrease the field current which in turn increases/decreases the output at the "D" connection and keep the dynamo output voltage suitable (~27V ?) to charge the battery and operate the system safely.I will replace the old cutout relay with a diode in series to prevent the reverse current from the battery into the dynamo when its voltage (the battery) is higher.Can you suggest an electronic regulator circuit to do this function? Are there any ICs that can do this regulation?

author: richard.cs
author_rank: Super Contributor
timestamp: March 02, 2016, 11:18:43 pm
content: Take a look at this circuit as a starting point:http://ludens.cl/Electron/dynareg/dynareg.htmIt would need some changes to work on 24 V.Is your electromechanical regulator faulty? They are usually fairly easy to repair and adjust. The one on my car is 49 years old and still works well, I haven't touched it in the 6 years I've had the car.(Edited to fix link)

author: Zero999
author_rank: Super Contributor
timestamp: March 03, 2016, 08:57:49 am
content: An automotive alternator regulator IC may do, but most of the ones I could find are for 12V, so the circuit on the datasheet would need to be modified for 28V operation.

author: Rerouter
author_rank: Super Contributor
timestamp: March 03, 2016, 09:09:39 am
content: Most circuits i can find look to essentially be a glorified current limited voltage supply, inner loop is a current limiter, measure the current across a resistance and regulate feild current based on that (single op amp circuit, look up constant current source here on eev), outer loop is a voltage loop, more of a comparitor with a lot of integration, when the voltage limit is reached it begins winding back the feild current strenght from the current limiting loop,So i can forsee this being 2 op amps, a heavy pass element, some transistors, and a handful of passives,

author: Zero999
author_rank: Super Contributor
timestamp: March 03, 2016, 08:05:39 pm
content: The usual way is to PWM the field current and adjust the duty cycle to keep the output voltage at the correct set point. If an automotive alternator IC is not suitable then a PWM switched mode power supply controller may work.

author: 3Deye
author_rank: Contributor
timestamp: March 04, 2016, 12:57:06 pm
content: Quote from: richard.cs on March 02, 2016, 11:18:43 pmVery useful project, I will simulate the circuit and will modify it to work on 24V. Do you know how to model a dynamo in Orcad SPICE simulations?QuoteIt's not faulty, but I want to replace it with an electronic one as a learning project.Quote from: Hero999 on March 03, 2016, 08:57:49 amThank you for suggesting the alternator regulator IC. Will research more about it.Quote from: Rerouter on March 03, 2016, 09:09:39 amQuote from: Hero999 on March 03, 2016, 08:05:39 pmThank you guys. Actually I don't know the required field voltage and current for this dynamo, is there any typical figures? How can I measure it?In general, what are the specifications of the dynamo that should be clear to me to be able to design the compatible regulator for it? The specs I have are its output voltage (28V), output current (~107A) and that's it. I think The missing specifications are the field winding polarity, voltage and current. How can I measure them? Is there any other missing specs?

author: Zero999
author_rank: Super Contributor
timestamp: March 04, 2016, 02:01:59 pm
content: The required field current will depend on the load and shaft speed. The higher the load current and slower the shaft speed, the greater the required field current.