Evaluation of Aliexpress sourced EBM315 battery packs (for DB3DL2)

In Repack of Hikoki / Hitachi EBM315 battery pack (DB3DL2) I discussed the repack of a battery pack. At the same time I also ordered a no-name replacement 1.5Ah battery on Aliexpress for $25 incl shipping… with some reservation as most batteries I have purchased on Aliexpress have failed to deliver half of the rated capacity.

So, the battery arrived and I tested it, the purple trace above, and I was pleased to see that it exceeded the rated capacity a little.

So, I purchased another from the same seller, and it duly arrived, and to my surprise, it exceeded rated capacity by 30%.

Both batteries recharge properly on the Hitachi / Hikoki charger.

Time will tell whether they are good value. In any event, they use screws to hold the cap on so they can probably be repacked with good cells.

Repack of Hikoki / Hitachi EBM315 battery pack (DB3DL2)

I have had a Hitachi DB3DL2 ‘pencil’ type cordless screwdriver for about 12 years, and one of the supplied two batteries (EBM315 1.5Ah) has just failed. This is not the first failure, the charger failed after about five years use and the LED push button became electrically leaky flattening the battery so the push button was removed. The second battery is still working, but at about 65% capacity.

It is actually a really good tool to use, and so worth trying to extend its life. To that end:

  • I purchased a new genuine Hikoki (new name for Hitachi -Koki) charger on Aliexpress for about $80 shipped (they are more like $150 locally);
  • I purchased an after market EBM315 1.5Ah battery on Aliexpress for about $25 shipped;
  • I purchased locally two Panasonic NCR1650B unprotected 3.4AH 18650 cells to repack the two original batteries; and
  • repacked the failed battery.

Above is a capacity test of the new Aliexpress 1.5Ah battery and the working 14 year old Hitachi battery. The little squiggles are concerning, to be further investigated. It is my experience that most rechargeable batteries purchased on eBay and Aliexpress grossly fail to meet specified capacity, the one is a welcome change… though note the quite low cell voltage to achieve rated capacity. Continue reading Repack of Hikoki / Hitachi EBM315 battery pack (DB3DL2)

Paralleling two synchronous AC generators – phasor diagram with AVRs

This article Paralleling two synchronous AC generators presented phasor diagrams for two synchronous generators in parallel, and Paralleling two synchronous AC generators – simple AVR discussion discussed a simple automatic voltage regulator system that can be used to share two identical machines.

To recap, the first configuration presented follows.

Above is a phasor diagram of two machines of the type discussed in parallel. This is just after ACB closure, and they are not well adjusted in this case to allow visibility of the various phasors. Continue reading Paralleling two synchronous AC generators – phasor diagram with AVRs

Paralleling two synchronous AC generators – simple AVR discussion

Paralleling two synchronous AC generators explained synchronisation and parallel operation of two generators, discussing sharing of real and reactive power.

In that discussion, the engines were speed governed, but voltage was manually controlled by adjusting excitation current. The phasor diagram showed that there is a relatively large source impedance (dominated by the synchronous reactance), EMF is around 1.5 times Vt, and terminal voltage Vt will vary widely with changes in load as a consequence. Continue reading Paralleling two synchronous AC generators – simple AVR discussion

Paralleling two synchronous AC generators

This article discusses adding a second synchronous AC generator in parallel with a running synchronous AC generator.

For explanation, a simple context is used, two identical diesel engine driven generators with governed speed, no droop compensation, otherwise largely manual control, simple equivalent circuit of the machines. The complexity of other factors like  harmonic currents etc are not discussed.

The simple model is useful as it underlies practical machines and is a good configuration to introduce the main principles of the operation.

To avoid typos, some of the text uses Python formatting of complex numbers.

Prerequisites for paralleling three phase synchronous generators

Prerequisites for paralleling three phase machines are:

  1. same phase sequence (eg both A-B-C);
  2. nearly the same voltage; and
  3. nearly the same frequency, and eventually same phase.

(1) does not apply to a single phase machine. (1) is resolved at the time of wiring up the machines and circuit breakers used to connect them to the bus. Unless changes have been made to machines or wiring, sequence should not need to be checked. After any reconfiguration or wiring changes phase sequence should be checked by a competent person.

Phase sequence is checked using an instrument like one of these above. The left one is a small three phase motor, the right one is electronic and shows sequence with an LED. Continue reading Paralleling two synchronous AC generators

Synchronous generator – phasor diagram and explanation

This article offers a phasor diagram for one phase of a synchronous generator and explains the diagram.

System characteristics:

  • Load: vt=240, s=20000VAr; pf=0.85; and
  • Generator (s): s=20000VAr; pf=0.9; ra=0.04pu; xs=0.7pu.
    .

Above is the phasor diagram for generator #1 in a pair of parallel generators. Green is flux, cyan is armature current, magenta is voltage. Continue reading Synchronous generator – phasor diagram and explanation

Synchronous machine power formula

An expression found in most texts on synchronous machines relates power to the power angle δ. δ is the angle between the terminal voltage and the generated EMF (under the applicable load current).

\(P=\frac{|E|\cdot|V|}{X_s}sin \delta\\\)

V and E are RMS values, albeit sometimes with phase.

This article gives a derivation that exposes the underlying assumptions that are not usually mentioned.

 

Above is the phasor diagram of the machine in generator mode. Continue reading Synchronous machine power formula

Initial review of ECO-LFP210 LiFePo4 (LiFe) battery

A ECO-LFP210 10Ah 4S LiFePo4 battery was purchased on eBay for a solar powered project, cost about $65 delivered.

Above, the battery (the Anderson Power Pole connector is an addition). The battery incorporates a battery management system (BMS), so protected against over voltage, undervoltage, over current, and cell balance is preserved. Continue reading Initial review of ECO-LFP210 LiFePo4 (LiFe) battery

Ongoing MR16 LED failures & purchasing frustrations

We have around 25 MR16 LED lamps, half of which are almost never used, the other half probably average 4 hours per day, or ~1500 hours per annum.

Remember that greens touted this ‘green technology’ to have a life of 100,000 hours. More recently, claims have been moderated to 10,000 to 25,000 hours… but that is a single LED element alone, not a set of them, and it does not include failures of the internal and external drivers. IOW it continues the fraud of green lighting.

Above, the MR16 50mm LED lamp. Continue reading Ongoing MR16 LED failures & purchasing frustrations