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Project Honda Insight, Part 9 First Electricals

Moving the 12V battery, wiring the alternator and removing the hybrid electrics

by Julian Edgar

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At a glance...

  • Moving the 12V battery
  • Voltage drop testing of the new cable
  • Wiring the alternator
  • Removing the hybrid bits
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This series is based around a 2001 model hybrid Honda Insight.

The Insight remains one of the most aerodynamic and lightest cars ever made, with a Cd of 0.25 and a total mass of about 850kg from its 2-seater aluminium body.

The intent of the project is to turbocharge the engine, add water/air intercooling and programmable engine management, and then provide new high voltage batteries and a new electric motor control system.

The aim is to build a car with the best performance/economy compromise of any in the world.

The series so far:

Project Honda Insight, Part 1 – Introduction

Project Honda Insight, Part 2 – Fitting an Alternator

Project Honda Insight, Part 3 – Building an Airbox

Project Honda Insight, Part 4 – Intercooling Requirements

Project Honda Insight, Part 5 – Intercooling System #1

Project Honda Insight, Part 6 – Intercooling System #2

Project Honda Insight, Part 7 - Turbocharging

Project Honda Insight, Part 8 - Building the Exhaust

This issue: moving the 12V battery, wiring the alternator and removing the hybrid electrics

Starting the engine

With the turbo installed, water/air intercooling system in place, new exhaust bolted on and alternator fitted (but not yet wired), it was time to turn the key. With the Honda still up on its jack-stands, and with the 12V battery on the floor and jumper-leaded to the original wiring, the engine cranked for only a few seconds before bursting into life.

I bled the coolant and let the engine come up to temp to check for leaks – oil, air, exhaust or coolant! Thankfully, there were none.

Free-revving the engine caused the boost gauge to blip just a little, the standard engine management then shutting down the engine at about 3500 rpm (later I found a cam sensor problem was causing this rev limit). Getting any boost at all without engine load is encouraging – the turbo doesn’t appear to be overly large.

The next steps were to mount the battery in the boot, electrically connect the alternator and then remove the un-needed hybrid electronics and high voltage (HV) battery pack.

Moving the battery

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I chose to mount the 12V battery on the right-hand side of the rear compartment, on the raised area created by the body pressing that gives clearance underneath for the muffler.

A small metal battery tray was purchased and then modified to suit. The modifications involved nickel-bronze brazing two washers to the centre of the tray, giving reinforcement for the two 8mm bolts that hold it in place. Under the car, additional load-spreading washers were used.

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To stop the tray from rocking on the uneven surface, nuts were brazed to the underside of the tray and then bolts were screwed into the nuts, giving adjustable height spacers.

The battery hold-down strap was welded from a combination of steel strip and angle, designed to suit the stepped contour of the top of the battery case. Larger than normal (8mm versus 6mm) hooked tie-down rods were then used to secure the battery.

The tray was blasted and then powdercoated in wrinkle black.

The battery I chose to use is a DIN53L MF with a CCA of 500 amps. Its dimensions are 242 x 175 x 175mm.

This battery, which is larger than the standard 12V battery fitted to the Insight, was selected because of:

  • its physical size (it fits into the required space)

  • the fact that it is a sealed design with an external vent tube (this is required when a battery is mounted within the cabin)

  • it is larger in capacity than the Honda’s original 12V battery.

The last point needs expansion – why go for a bigger battery?

In the normal Insight, the 12V battery is almost redundant. It is needed to supply the 12V systems in the car (lights, instruments, ECU, etc) but because it is constantly charged via a DC/DC converter working off the high voltage (HV) battery, and because the HV battery also normally starts the car (via the hybrid electric motor), the 12V battery doesn’t need much capacity at all. Basically, it runs the radio when you’ve got the engine off!

However, in my modified car, the DC/DC converter will be gone. The modified Insight will then be just like a conventional car – an alternator charges the battery that in turn starts the car (luckily, a conventional starter motor is also factory fitted), runs the lights, powers the ECU, etc.

Furthermore, my car will have increased electrical loads over standard – there’s the water/air intercooler pump, I intend fitting electric heat seaters, and I already run additional driving lights.

Based around this changed electrical load scenario, I chose to fit the much bigger 12V battery.

Wiring the battery

So how to connect the new battery to the car’s wiring?

In the Insight there is already a heavy-duty lead that runs from the boot to the engine bay – it’s the power feed from the DC/DC converter. While this initially looks ideal, there is one issue with it – it’s a bit small to run the starter motor.

(Confused about this starter business? The standard Insight uses the HV electric motor to start the car - except in just certain circumstances, where the 12V starter is used.)

In fact, the DC/DC converter charge cable uses the same 4mm diameter thickness of copper as used on other Honda alternator charging systems of the era – despite the lead being about 5 metres long versus the less than 1 metre length of a conventional alternator charging cable!

I think at a pinch I could have used this cable, but it would be borderline on a cold day if repeated engine cranking were needed.

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So I removed this cable and ran a larger diameter cable in its place. The new cable is 7mm in copper diameter – just over three times bigger in cross-sectional area. With a bit of persuasion, the larger diameter cable was able to follow the same route as the original.

Under the bonnet I used a new termination post to join these three lugs:

  • new battery cable

  • feed to the starter

  • feed to the 12V system of the car.

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This termination post was used (rather than, say, soldering all three wires together) to also allow jumper leads to be easily used – just pull off the plastic cover and there’s the positive battery connection under the bonnet.

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Back at the battery end, a 100 amp circuit breaker was installed. This will trip if a short circuit develops in the main battery lead.

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On the negative side of the battery, a cable was run to the original earthing point used for the DC/DC converter. This comprises a block welded to the alloy body of the car. Unfortunately, my supplier of cable didn’t have the same size cable in both red and black: the black cable is therefore slightly thicker… a minor weight penalty.

All cables were terminated by soldering to lugs. Note: you need a very large soldering iron to do this… in fact, on one large lug, I very gently used my oxy!

Wiring the alternator

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The Denso-copy alternator uses a 12V output (a simple threaded stud) and a three-wire connector. The 12V output connects straight to the positive terminal of the battery – but what about the three wires?

These wires are for:

  • ignition positive 12V feed

  • dash warning light

  • alternator sense.

(Note: pin-outs for lots of alternators can be found via a web search.)

The ignition-switched wire powers the excitation coils in the alternator. As its name suggests, this is connected to a power feed that is live only when the ignition is switched on.

The alternator sense wire tells the internal regulator in the alternator what the battery voltage is. This is so that the alternator in turn knows how much to charge.

At first glance, you may wonder at the necessity for this sense wire - after all, couldn’t this simply be connected to the alternator output terminal, which in turn is connected to the battery? The answer is ‘no’ because there will typically be a voltage drop in the charging circuitry, and so the battery voltage itself should be directly monitored.

That’s the theory, but in many cars, people just connect the ‘sense’ wire to the starter motor solenoid or similar – this in turn is connected to the battery via a heavy gauge lead. So should I run the sense wire right back to the rear-mounted battery, or just connect it to the engine bay termination post? I did some voltage drop testing to find out.

Voltage drop testing

So where to connect the sense wire – to the battery or just within the engine bay?

The alternator is rated at 90 amps maximum output. In the case of the Honda, this is a little more than the nominal current draw of the starter motor. (The Honda uses a 1kW starter, and 1000 watts divided by 12.4 volts = 81 amps.)

So if the voltage drop of the long battery cable was measured during engine cranking, this would also give a good indication of the voltage drop when current was flowing the other way – from the alternator to the battery.

Measuring voltage drop is as easy as placing the multimeter probes at each end of the cable in question, and seeing what voltage is shown at maximum load.

As is almost always the case, measurement showed stuff that theory did not. Firstly, when cranking in 6 degree C ambient conditions, the voltage drop of my new bigger cable was 0.8V, falling quickly to 0.5 V once the engine got turning over.

Given the thickness of the cable, that voltage drop is surprisingly high, so I used a clamp meter to measure actual current draw. This measurement showed 132 amps!

That current draw is a lot higher than the calculated 81 amps, so what was battery voltage falling to? I measured this during cranking and found that it dropped from 12.3 to just 11 volts – obviously, the battery was not fully charged. But that’s a realistic scenario.

Even at 11V, a 1kW starter motor would be expected to draw 91 amps, so obviously the loaded-down starter actually draw more than you’d expect, given its rated power.

So where does this leave the alternator sense wire? A voltage drop at 132 amps of 0.8V corresponds to a voltage drop at 90 amps (max alternator output) of 0.5 volts. Thus if the sense wire were terminated in the engine bay, the battery would always be charged at a voltage (at least at high currents) of 0.5V less than ideal.

The result of the test? - I needed to run the sense wire right back to the battery.

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With the sense wire connected to the positive terminal on the battery, and with a small in-line fuse added to this cable for safety (arrowed), there were two alternator wires left – the ignition switched input and the connection for the warning light.

I couldn’t find an ignition-switched terminal under the bonnet, so the ignition-switched wire was run back into the cabin and terminated temporarily on an appropriate ignition-switched supply.

The alternator warning light wire normally runs to the light, with the other side of the light connected to +12V. During testing, I used a small 12V filament lamp – and the light glowed as it should. However, in the finished car I will use the MoTeC dash to monitor battery voltage, so no alternator warning light is needed. (If the alternator stops charging, the battery voltage will be low, so allowing the triggering of a dash warning.) I therefore chose not to fit the warning light.

Note: in the case of this Denso-copy alternator, the alternator worked fine without the presence of the warning light. Some alternators, however, need the warning light in place to function.

So what are the results? The alternator output, even at idle, is excellent.

I was able to see 70 amps charge coming from the alternator at 1000 rpm engine speed – the alternator is rated at 90 amps, but getting this much load on it was difficult!

Belt slippage

During alternator testing, the drive belt started to slip, producing that characteristic squeal.

This worried me a great deal: the belt ‘wrap’ around the crank pulley is less with the alternator fitted than in the factory system – and it’s very hard to configure the belt drive system in any other way. I tightened the belt but at over 3000 rpm, the belt still slipped. Any tighter, and the bearings in the idlers became audible.

I then wondered if the belt had some grease or coolant on it, making it slippery. I sprayed on some degreaser as the belt rotated, and some black stuff dripped off. I then went searching for a stronger cleaner and found some in the bathroom – tile and grout cleaner! This stuff is so powerful it burns the hairs in your nose… After I sprayed this on the rotating belt, it stopped slipping.

Touch wood that it’s now OK – but the belt will certainly need to be kept clean.

Removing the hybrid bits

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With the car initially to be run as a non-hybrid turbo three-cylinder, the hybrid electronics and battery pack could then be removed. (Replacements will come in the form of new generation batteries and electronic controls, further down the track.)

This process was as straightforward as switching off the battery pack, donning high voltage protection gloves, standing on a rubber mat and then unbolting and pulling off parts.

Note: Never work on the high voltage parts of a hybrid vehicle without taking full safety precautions.

As the parts came out, I weighed them (bathroom scales, so not accurate down to grams).

The DC/DC converter and electric motor controller weighed 13kg, and the battery pack (complete with cooling fan) 32kg. Throw in a few kilograms for the rest of the parts (two ECUs, another cooling fan) and it adds up to about 47kg – or only 5–6 per cent of the total car mass.

Next: aaaaghhhh - finding out that the just finished alternator bracket needs a complete rebuild….and, more positively, driving the car on the road with the standard engine management

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