Power Steering failure when in use battery drops 13.5 to 8v

Technical discussion on converting internal combustion to electric
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Stephan
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Power Steering failure when in use battery drops 13.5 to 8v

Post by Stephan » Mon, 30 Sep 2019, 22:49

Hi,

Finally after all my car conversion issues, I am testing my car by driving it a few meters on my driveway. I am not allowed on the road yet.

For power steering I have a basic ev conversion set up with a DCDC (around 600W) and a small 12v battery (PC680 - 24 ah) and an Astra PS pump installed.

1. Problem description
The pump seems to function based on it typical noise. When turning wheels on the drive way it seems to work.
With first few test drives it first appeared ok.
Then after more test drives, one in the dark with head lights and all systems drawing some power, it suddenly appeared to be a real issue.
The car stops driving due to voltage drop from 13.5 to 8v.
After finding out I tested again standing still and no lights on and even then it drops when turning the wheels from 13.5 to 9-10v.

2. How to diagnose the problem?
I have no experience with power steering nor a voltage drop like this.
Some possible reasons I can think of:
a. the 12v battery needs replacement
b. the DCDC is not strong enough
c. a problem with the power steering pump and it draws much more or other problem causing the voltage to drop.

I do not have the money to replace all the above nor spare parts to test with.

Progress:
I used a spare 12v and tested the problem with a more powerful 48ah battery but still the same problem.
I suspect that the high pressure pumps the fluid without leak. I can't see any leak.
I suspect that there is no leak in the low pressure as I don't see bubbles.
There seems to be an electrical switch on the high pressure hose. I am currently not using it. I was told that this can be used to switch the pump off when there is enough pressure. I have never been bothered to do so but now it comes back in my consideration due to the high power consumption and the problem of this constant high draw of power.

Next:
What should I do first?
I want to repeat this test and isolate the power steering by connecting it only to this 12v test battery and nothing else.
I want to measure the amps it draw. For now I assume it draw between 30-60 amp.
Should I consider a second DCDC, one only for the power steering?
Should I add a ground wire, one that is closer to the actual pump and chassis. I now only run a thick cable directly to my battery B-.
My electrical knowledge is limited and I do not understand when and why grounding would be needed.
Should I consider a better newer pump, would that draw less and be more reliable, and maybe quieter?
Should I get my car certified without power steering, is it a engineering requirement?
Others?

-thanks
Thanks for your support, Stephan

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jonescg
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Re: Power Steering failure when in use battery drops 13.5 to 8v

Post by jonescg » Tue, 01 Oct 2019, 06:34

The Astra power steering pump will draw 25 amps just to maintain pressure, and as much as 60 amps when ramping up to full lock. It could be that your DC/DC is not up to the task?
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Richo
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Re: Power Steering failure when in use battery drops 13.5 to 8v

Post by Richo » Tue, 01 Oct 2019, 12:39

Stephan wrote:
Mon, 30 Sep 2019, 22:49
What should I do first?
Post us a photo. :!:

What size cables joint the DC/DC to the 12V battery?
So the short answer is NO but the long answer is YES.
Help prevent road rage - get outta my way!

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Re: Power Steering failure when in use battery drops 13.5 to 8v

Post by Richo » Tue, 01 Oct 2019, 12:53

The 12V should be able to cope with the load.
The DC/DC should be able cope with the load too.
8V is quite a drop - last legs in fact.

Check all your 12V connections are clean and tight.

Am I to assume the battery has been in there for a while since I see some posts from a few years back.
I'd guess the battery is on the way out.
So the short answer is NO but the long answer is YES.
Help prevent road rage - get outta my way!

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Re: Power Steering failure when in use battery drops 13.5 to 8v

Post by Stephan » Sat, 12 Oct 2019, 13:20

Thanks for your replies. It helps me to decide what to do next.
1) Yes this battery is in the car for a little over 2 years. The battery is very weak. And the DCDC does probably all the work. And with only 600W this seems not enough. Note that I have my car 2 years, but never been able to drive it yet. Test driving yes, but not approved for the road, after failing engineering 1.5 year ago. But bottomline for this problem, the battery is nearing end of life. And I am not convinced that replacement is the solution. Is a PC680 300 dollar 24ah battery enough with my 600W 40ah DCDC? Or should I split the power steering up and connect to a second 12 battery and also replace the old 680, or both.
2) And yes, the voltage drop is probably not due to bad connections or wires that are the right size for this 30-60amp load. I was glad to hear you confirming that 30-60amp is normal when ramping up, I thought so but was not sure.
3) Today I did two tests. Both confirming that the problem can be fixed with a larger and/or healthier battery. I hooked up two types of larger battery and separated the power steering from the rest. Test result is fine, no issue with both larger 70ah 'normal' 4x4 car battery and also with another 'homemade' very powerful 12v battery.

Options
1. Replace my PC680 24ah battery with another 680 'AGM' for 300$ or a 160 dollar non-AGM alternative
Consideration is that this setup with the 600W max 40ah DCDC may at times not be enough to drive this car during a 30-40 minute drive.
2. Add a second 12v battery. If what type of battery, and would I be able to charge both 12v battery with one DCDC, or does this require a second DCDC?
Consideration, connecting to one DCDC basically means I run the two batteries in parallel all time. I am not sure if this is what I want, as I preferable use two different size batteries; I am thinking of adding this 70ah 4x4 car battery.
3. Upgrade only the DCDC to a heavier model and keep the 680, or just refresh with this 160 dollar replacement version.
4. Is there an alternative power steering which is less noisy and consumes less power?

Any ideas and suggestions are welcome!
- Stephan
Last edited by Stephan on Sun, 13 Oct 2019, 08:41, edited 1 time in total.
Thanks for your support, Stephan

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Re: Power Steering failure when in use battery drops 13.5 to 8v

Post by brendon_m » Sat, 12 Oct 2019, 15:01

Think of it like water. You have a bucket with 24 litres in it (the pc680) (with a crack in the side by the sounds of things.)
You have a hose that pumps ~40 litres per hour (600w dcdc) and a hole in the bottom that let's out 25 litres all the time and sometimes up to 60L(power steering).
Maybe 35L on average.
And then there is another hole with say about 10-20L coming out (all the rest of the 12v electrics).

Im going to use a hours driving for ease of maths

So 24L bucket with a 40L/h hose makes 64L available but 50ish litres come out over that hour. So the battery will be 2/3rds flat after an hour. That will kill the battery fairly quickly.

It should keep up and not drop out however this relies on the battery starting off full and being recharged after driving has finished.

Sounds like the pc680 is dead (get it tested to be sure) if you parallel it with another battery it might drag the new one down and kill it, So I'd ditch it entirely.

The 70ah battery will give you a bit more head room.

An upgraded dcdc will insulate you a bit more from a stuffed 12v battery but I think if you just drop a new 70ah battery in you should be good. If the dcdc fails entirely then you still have enough in the bucket to get you through the whole trip and you won't be cycling it quite so much so in theory it should last longer.

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Re: Power Steering failure when in use battery drops 13.5 to 8v

Post by brendon_m » Sun, 13 Oct 2019, 07:49

Found this, pretty pricey and you would need to talk to your engineer but it's definitely more elegant.

https://www.ultimatepowersteering.com.a ... steer-kit/

They also do universal hydraulic kits
https://www.ultimatepowersteering.com.a ... pump-kits/
7-15a at idle and 45-55 while steering, so slightly less power and probably quieter.
Also expensive. But it is new compared to a 2nd hand astra pump, so probably fair.
Personally I like the idea of the motor on the steering shaft and it is a kit designed for the task however steering and brakes are a minefield for licensing

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Re: Power Steering failure when in use battery drops 13.5 to 8v

Post by brendon_m » Sun, 13 Oct 2019, 07:55

brendon_m wrote:
Sat, 12 Oct 2019, 15:01
You have a hose that pumps ~40 litres per hour (600w dcdc) and a hole in the bottom that let's out 25 litres all the time and sometimes up to 60L(power steering).
Maybe 35L on average.
And then there is another hole with say about 10-20L coming out (all the rest of the 12v electrics).
Thinking about this, it will mean your headlights will dim when steering, especially towards the end of the drive, so a bigger dcdc, or just a second one might be in order regardless.
Unless you replace the power steering with something more efficient.

I wonder if a 144vdc pump can be sourced from China, like the aircon compressors?

Stephan
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Re: Power Steering failure when in use battery drops 13.5 to 8v

Post by Stephan » Sun, 13 Oct 2019, 09:39

Thanks Brandon I think this comparison with water flow and volumes if very useful!

4.) replace the power steering pump.
a) I also looked into the option of a pump on the steering shaft but too complex for now
b) the model as in the video as in the link above, yes it may be slightly better. I like my version as an integrated bottle/pump for now more
c) for now I will keep the astra pump
- looking into the high and low pressure lines I double check on leaks and seems fine
- looking at the fluid level, there is not a clear indicator other than this 3-4 cm pin on the lid which is not touching the fluid (tiny top is what I will do)
this was probably because I never top up after initial fill, after first test drive this must have dropped a little. I hope it reduce some of the noise
- still looking at other ways of sound mufflers

3.) Upgrade DCDC
a) my current version seems to work fine
b) I like the idea of adding redundancy and for 220 dollar I can buy the same doubling capacity. I am thinking of using it with a second 24ah battery. See below.

2.) Two 12v batteries instead of one
a) I like the idea of adding redundancy also for the 12v battery in case same bad happens and ending waiting for road side assistance and being able to fix it
b) I consider two identical 24ah and with same physical size

1.) 12v battery remove and replace
a) key question is with which battery to replace this
-I am convinced that my old 680 need to be replaced.
- due to physical space restriction the large 70ah does not fit at same spot. I expect more engineering challenge with larger 70ah installation
-to reduce the amount of recabling, if I add a second battery I expect one seperate cable for the steering pump and a new DCDC cable to new DCDC.
b) As explained above I want to stick to the 680 size (24ah) but do I need this AGM Gell based version which seems to charge 5x faster
c) do I need something that charges 5x faster while I keep the DCDC on all times even when KSI is off?
d) AGM durability may be another aspect but at this stage I just need this car on the road
e) AGM is about 150 dollar extra which is twice as expensive. In other words two non-AGM for the same price

Note that I am on a budget. Also I don't have much (cabling) tools. My design principle is to recycle as much as possible. I do add by exception some new parts.

Shortlist Options
1 - PC680 replacement. At a minimum it needs to hold charge and is reasonable healthy. Expected cost 50 -300 dollar
2 - Purchase second 12v battery and new DCDC -
online: https://www.evolutionaustralia.com.au/p ... -converter
plus second used or new PC680. - expected cost 275 -525 dollar
plus two non-AGM 24ah - expected cost 375 dollar
plus used 70ah battery - 225 dollar

Minimum 275 dollar and max 525 dollar depending what to do.

I will check coming weeks at AEVA Sydney Expo how I can progress this. I am planning to demonstrate my car there.
Thanks for your support, Stephan

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