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0

You could use a 7.4V Battery and a DC/DC converter (buck type) with 3.7V output voltage (Such a task is the main purpose of DC/DC converters).


2

BQ2002 NiMH Charging Circuit not working Thank goodness your circuit does not work. Did you read the datasheet for the BQ2002? The datasheet clearly shows how to connect the controller: You have no connection from Bat to the NiMH you are charging ....so no voltage sensing. You have no current limiting or detection in the charge path, so no way to control ...


0

From what I understood of a quick glance at the datasheet, seems that it's programmed at the factory and you'd have to contact the manufacturer.


0

If your discharge is 250mA with rate of 0.7, your true discharge is then 175mA. So with battery of 3716mAh it will last for a 21.23 hours. With a charge from SP of 0.59W (with 3.81V it gives 155mA), your discharge changes to 20mA and the battery will last for a 185 hours. However, don't expect all of power from SP will be delivered to battery, some will ...


0

You should allways keep the cells balanced in order to mantain a balanced power draw from each cell. If, by come reason, one of the cells starts having under voltage, you might overload the other risking a ball of smoke... You know what they say: Balanced LiPo is a healthy LiPo!


1

If the cell capacities are well matched and they have equal charge then they shouldn't need to be balanced while charging. So... When you get the battery, measure the voltage on each cell via the balance connector. If they are within 0.03V of each other then it should be OK to charge the pack via the T connector. When charging for the first time, monitor ...


1

Balancing them when it's not strictly necessary won't cause any issues. NOT balancing them when it IS necessary WILL cause issues. Dangerous, fire or explosion based issues. I'd take the safe approach if I were you.


3

It is possible, but not advisable. First a little background information: Putting batteries in series adds the voltages together. This does not add the capacities together. You put batteries in parallel to add the capacity. This applies to current as well as capacity. You normally put batteries of the same size together to make a larger one. Lithium ...


-1

DC-DC boost regulator will be more efficient than any Alternator (<< 70%) with low voltage protect set at 13V when 12V alternator is charging. Ref


2

simulate this circuit – Schematic created using CircuitLab Figure 1. OP's proposal redrawn. With SW1 in position shown BAT2+ will be shorted to U1's BAT- which according to the TP4056 datasheet is supposed to be connected to ground so the arrangement is likely to have a very unhappy ending. simulate this circuit Figure 2. A circuit with less ...


1

Maybe your power bank or the power management system of the phone itself is not able to supply enough power for charging and power for normal phone operation. I.e. you may only charge while the phone is in stand-by or operate the phone normally but without charging. If e.g. charging (+ stand-by) consumes 7W and nomal operation consumes 5W , the power system ...


0

You have two problems. The MPPT charge controller is not charging the battery. The battery is not reaching 100% I would start by giving the battery an Equalizing Charge. The battery may be okay. First thing to do is measure the output voltage of the PV while the MPPT is (or should be) charging. Do this periodically throughout a sunny (or mostly ...


1

If you are not worried about efficiency or the life of the batteries, a buck regulator with a decent size capacitor on the PV side would do. Set to 13.8V to float charge the batteries. Bare in mind that lead acid batteries can deliver 100's of amps, so are a potential fire hazard when things go wrong if not suitably fused. To do it properly, find a ...


4

BQ2002 and similar ICs don't actually see the charging current path through them. They are just controllers, they don't regulate by themselves. They have an output (the CC pin) which is used to indirectly control the external, high-current passing element. You can have a look to a reference design provided by TI. The CC output controls a LM317 which is used ...


2

Cell protection does just what it says: it protects a single cell. A common chip for single cell protection is the DW01 This chip monitors the voltage across the battery and the current through the MOSFETs. It opens the MOSFETs (which disconnects the battery) when the voltage across the battery becomes too high, too low or when the current becomes too high....


1

Just make sure 18650 battery cells mechanically fit, properly elecrically connected to tablet or protection circuit from original battery (if present) and recommended to have end discharging voltage of at least 2,7V ( must be written in datasheet ). Tablet will charge the batteries to voltage it can accept anyway and upgrading charger to more powerfull one ...


1

Where did you read the battery specification about 3.7V +-5%? Usually, All these batteries are same with 4.2 Vmax. You will need more powerfull charging circuit to handle higher current of 4 batteries, and balancer board also. Maybe you will have to deal with protection and identification circuit, if the original battery has more than two wires (NTC, ...


1

Use P-channel Mosfet (better solution for high-side switch) - no need higher voltage than Vsupp. Edit: Something like this: Vsupp = 18V PWM = 0-5V Edit: LTspice simulation of buck (green is Gate voltage):


1

Two general things: Do not drive the MOSFET directly from your MCU. Well that actually depends .on your switching frequency. But if you want to quickly switch on and off your FET to reduce switching losses, you need to source and sink a lot of current . Also your MCU voltage is limited but you want to overdrive the MOSFET to switch on faster and reduce ...


1

An MPPT controller only works at the Maximum Power Point drawing Maximum Power, if it can dump whatever power it draws into whatever is downstream. If that's a battery, and it's fully charged, then the MPPT has to be told to stop being an MPPT, otherwise it will damage the battery. As long as it is of limited duration, 15v is OK on a lead acid battery, in ...


1

Thanks for the help everyone. Turns out I have crappy resistors. They are "rated for 100 watts" (I said 50W in the diagram but even that was too generous). They warmed up pretty quick; I read up 250C (!!!) with a reasonably accurate infrared thermometer after letting it sit for just a few minutes. After disconnecting power I measured resistance again ...


-2

One of your readings is incorrect if it does not match this,


2

I don't seem to have enough reputation to comment, but something seems off. You're reading 35V across the 8 ohm resistor? This would mean from ohms law 35V/8ohm = 4.375A. so something is off if you're producing too different measurements. in other words, for 3.5A to flow through the resistor, the drop would be 3.5A*8ohm=28V, but you're seeing a drop of 35V....


0

I've a similar project ongoing. My answers based on my research is: Don't go with the UltraFire batteries there are so many fakes and the test I've seen of them is that the Ah is far much lower than the specs! As can be seen here: Batteries test various Li-ion types Regarding one or two cells it's a lot easier to go with one cell. You will only need ...


0

If your use case has pretty constant operating conditions wrt current rates, duty cycle, ambient temperatures etc, and you have the gear and knowledge to determine actual SoC via controlled constant load testing down to 0% under "average" conditions and the batteries are proactively replaced before they age much, then extensive test benchmarking will ...


0

Yes the SparkFun board is designed for exactly that. The limiting factor is the JST connector, but as long as that 6A rate is fort short runtimes you should be OK. Test the temperature rise in hot ambient conditions, inside your enclosure at the XH wires and plug, holding 6A for say 10x longer than you imagine. The other issue is the very low charge rate, ...


1

There are an infinite number of profile paths to get to a given SoC. At a low enough current rate, holding Absorb / CV long enough can overcharge even at a much lower voltage. Overcharge meaning "losing significant life cycles if done consistently". The good news is, very little usable SoC Ah capacity is lost by incrementally dropping Voltage, or stopping ...


0

Can't help with the chip/diode specifics, but here's some battery basics. Each batt model has different specifications for Absorb voltage, Float voltage and endAmps, the tapering current point defining Full, at which voltage is allowed to drop from Absorb to Float. I would not buy a battery where those specs are not available, as well as e.g. charts ...


4

I want to use to charge a (14.8V nominal) Li-ion battery. Any voltage above 16.8V (full charged) will do, as long as it's not too high. (Should I even consider using 27V directly?) This is absolutely wrong and dangerous premise. Li-Ion batteries must be charged wich CC (constant current) and then CV (constant voltage) algorithm, and the CV level must ...


4

A voltage divider is not the right tool for this job. You need a voltage regulator. Considering that you are trying to charge a lithium ion battery, you probably ought to use a charge controller rather than a simple regulator. You need to stop and reconsider your project. A voltage regulator will reduce the voltage. The problem is that you need more ...


1

Your bike has a 72V 20Ah battery which is 1440Wh. The portable battery is 155Wh, so it will not charge the bike battery from flat to fully charged. It depends how much you need to charge it after each use. Based on the 155Wh and 42Ah, the portable battery must be 3.6v internally.


1

There are a great number of modules associated with a modern EV. I suggest you view some of the excellent video series produced by Professor John Kelly at Weber State. In the particular video I linked, he explains differences for the DC fast-charge compatible model of the Bolt. If you follow the source for the Wikipedia article you linked (which you should ...


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