Modifying Hitachi TRK-3D8S, batteries and amp circuitry

[wastenotwantnot]

Hello, I have recently acquired one of these:



Apart from wanting to add some additional drivers at either end which will require modifying the chassis, I am also considering changing the power source. The additional drivers may make the existing D cell placement a problem, and I am concerned about runtime with the additional power drain. The current arrangement is 8 x D cells to give 12V with a physical switch on the reverse to flick between the internal 240V PSU and batteries. There’s no charging capability. I can find on Amazon and various places what appear to be high capacity 10,000mAh cells, but I am thinking these might be rubbish. I am wondering if moving to a mobility scooter style 10Ah lithium “block” might be better but am looking for suggestions possibly including charging circuitry.

The other issue I have is this switch:



It’s a 3 position switch that enables/disables 2 amplifier circuits. In the top position, both the mono bass amp and the stereo mid/tweeter amp are enabled. In the middle position the bass amp is off (this is the issue) and in the bottom position both amps are off and the mic is on. The middle position is essentially useless and it annoys me greatly that such a switch position even exists. No one is ever going to listen to it like this. Without the bass circuit, you only get tinny music.. just take a 3 way and unplug the bass, that’s what it sounds like!

Here is a pic of the PCB:



With what I believe to be the contacts that are connected in each position. I am considering cutting the traces for the top 2 positions to repurpose this switch, but I need help figuring out if cutting these traces will kill another part of the circuit.

What I’m trying to end up with is:

Top: powering 2 x 12V TPA amp boards (1 for new drivers, 1 for original 3 drivers)
Middle: just the new TPA amp going to the original 3 drivers
Bottom: unchanged

Original 2 on board amps will not be needed or used if this comes together as planned. I am hoping that replacing the original 2 on board amps with a newer TPA chipset will draw less power as well. I hope this makes sense. :-/

I have the service manual:  hfe_hitachi_trk-3d8_service.pdf (0 kB - downloaded 37 times.)

But not having an electronics background, I am not sure where to begin.

I would be ever so grateful for any pointers in helping change the batteries and “repurposing” this switch.

[wastenotwantnot]

I’ve been looking at batteries like this: https://www.ebay.co.uk/itm/10Ah-20Ah-30Ah-50Ah-100Ah-12V-Lithium-Battery-LiFePO4-Solar-Battery-Golf-Trolley-/324538407634?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l49286&mkrid=710-127635-2958-0

Although I cannot find any information on the charging circuitry that is needed to charge something like this. All the charge controllers I can find see to be focussed on 1-6 18650 (or similar) cells. Or for the 12V blocks/packs like the above, they seem to be solar units.

I wouldn’t ever consider getting a lithium pack from somewhere like AliExpress, but I was looking at this: https://a.aliexpress.com/_uR75Fw

And it seems to suggest that the charging circuitry is included in packs like this. Presumably one would just wire one side (male jack) to the 12V input on the PCB, and the female jack could be mounted out the rear of the chassis?

[wastenotwantnot]

I’ve now sorted the switch issue but I am still after recommendations for a battery. Anyone?

[Terry Bites]

I'd go for NIMH to avoid electroboom box.

[wastenotwantnot]

I'd go for NIMH to avoid electroboom box.

Is something like this plausible?

Amazon Basics D Cell Rechargeable Batteries 10000mAh Ni-MH, 4-Pack (Appearance may vary) https://www.amazon.co.uk/dp/B07PHCWNH1/ref=cm_sw_r_cp_api_glt_fabc_Y3A2FSKYTXESVQTQB1N3

The capacity seems very high but this is the kind of thing I am after. I was looking for a larger size, something similar to a motorbike battery. Do you have any recommendations?

Edit: ok, so looks like I’d be stuck on size Ds for something like this, but I get the pros of not burning the house down with the lithium cells.

Assuming 10 x Size D cells to total the 12V needed, I’m now looking for something to charge them, as it won’t be easy to remove the cells once the unit is completed.

Looking at a charging board, I’m not finding much apart from things like this: https://www.ebay.co.uk/itm/1-2-24V-2-4-3-6-12V-Ni-Cd-Ni-MH-NiCd-Batteries-Charger-Module-Charging-Board-/373726804945?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l49286&mkrid=710-127635-2958-0

Seems to be a 300mA limit though. :-(